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1.1 ! root 1: Phil's Pretty Good Software ! 2: Presents ! 3: ! 4: === ! 5: PGP ! 6: === ! 7: ! 8: Pretty Good Privacy ! 9: Public Key Encryption for the Masses ! 10: ! 11: ! 12: ------------------------- ! 13: PGP User's Guide ! 14: Volume II: Special Topics ! 15: ------------------------- ! 16: by Philip Zimmermann ! 17: Revised 6 Mar 93 ! 18: ! 19: ! 20: PGP Version 2.2 - 6 Mar 93 ! 21: Software by ! 22: Philip Zimmermann ! 23: with ! 24: Branko Lankester, Hal Finney, and Peter Gutmann ! 25: ! 26: ! 27: ! 28: ! 29: Synopsis: PGP uses public-key encryption to protect E-mail and data ! 30: files. Communicate securely with people you've never met, with no ! 31: secure channels needed for prior exchange of keys. PGP is well ! 32: featured and fast, with sophisticated key management, digital ! 33: signatures, data compression, and good ergonomic design. ! 34: ! 35: ! 36: Software and documentation (c) Copyright 1990-1993 Philip Zimmermann. ! 37: For information on PGP licensing, distribution, copyrights, patents, ! 38: trademarks, liability limitations, and export controls, see the ! 39: "Legal Issues" section. ! 40: ! 41: ! 42: Contents ! 43: ======== ! 44: ! 45: Quick Overview ! 46: Special Topics ! 47: Selecting Keys via Key ID ! 48: Separating Signatures from Messages ! 49: Decrypting the Message and Leaving the Signature on it ! 50: Sending ASCII Text Files Across Different Machine Environments ! 51: Leaving No Traces of Plaintext on the Disk ! 52: Displaying Decrypted Plaintext on Your Screen ! 53: Making a Message For Her Eyes Only ! 54: Preserving the Original Plaintext Filename ! 55: Editing Your User ID or Pass Phrase ! 56: Editing the Trust Parameters for a Public Key ! 57: Checking If Everything is OK on Your Public Key Ring ! 58: Verifying a Public Key Over the Phone ! 59: Using PGP as a Unix-style Filter ! 60: Suppressing Unneccessary Questions: BATCHMODE ! 61: Force "Yes" Answer to Confirmation Questions: FORCE ! 62: PGP Returns Exit Status to the Shell ! 63: Environmental Variable for Pass Phrase ! 64: Setting Configuration Parameters: CONFIG.TXT ! 65: TMP - Directory Pathname for Temporary Files ! 66: LANGUAGE - Foreign Language Selector ! 67: MYNAME - Default User ID for Making Signatures ! 68: TEXTMODE - Assuming Plaintext is a Text File ! 69: CHARSET - Specifies Local Character Set for Text Files ! 70: ARMOR - Enable ASCII Armor Output ! 71: ARMORLINES - Size of ASCII Armor Multipart Files ! 72: KEEPBINARY - Keep Binary Ciphertext Files After Decrypting ! 73: COMPRESS - Enable Compression ! 74: COMPLETES_NEEDED - Number of Completely Trusted Introducers Needed ! 75: MARGINALS_NEEDED - Number of Marginally Trusted Introducers Needed ! 76: CERT_DEPTH - How Deep May Introducers Be Nested ! 77: BAKRING - Filename for Backup Secret Keyring ! 78: PAGER - Selects Shell Command to Display Plaintext Output ! 79: SHOWPASS - Echo Pass Phrase to User ! 80: TZFIX - Timezone Adjustment ! 81: CLEARSIG - Enable Signed Messages to be Encapsulated as Clear Text ! 82: VERBOSE - Quiet, Normal, or Verbose Messages ! 83: INTERACTIVE - Ask for Confirmation for Key Adds ! 84: Protecting Against Bogus Timestamps ! 85: A Peek Under the Hood ! 86: Random Numbers ! 87: PGP's Conventional Encryption Algorithm ! 88: Data Compression ! 89: Message Digests and Digital Signatures ! 90: Compatibility with Previous Versions of PGP ! 91: Vulnerabilities ! 92: Compromised Pass Phrase and Secret Key ! 93: Public Key Tampering ! 94: "Not Quite Deleted" Files ! 95: Viruses and Trojan Horses ! 96: Physical Security Breach ! 97: Tempest Attacks ! 98: Exposure on Multi-user Systems ! 99: Traffic Analysis ! 100: Cryptanalysis ! 101: Legal Issues ! 102: Trademarks, Copyrights, and Warranties ! 103: Patent Rights on the Algorithms ! 104: Licensing and Distribution ! 105: Export Controls ! 106: Computer-Related Political Groups ! 107: Recommended Readings ! 108: To Contact the Author ! 109: Appendix A: Where to Get PGP ! 110: ! 111: ! 112: Quick Overview ! 113: ============= ! 114: ! 115: Pretty Good(tm) Privacy (PGP), from Phil's Pretty Good Software, is a ! 116: high security cryptographic software application for MSDOS, Unix, ! 117: VAX/VMS, and other computers. PGP combines the convenience of the ! 118: Rivest-Shamir-Adleman (RSA) public key cryptosystem with the speed of ! 119: conventional cryptography, message digests for digital signatures, ! 120: data compression before encryption, good ergonomic design, and ! 121: sophisticated key management. ! 122: ! 123: This volume II of the PGP User's Guide covers advanced topics about ! 124: PGP that were not covered in the "PGP User's Guide, Volume I: ! 125: Essential Topics". You should first read the Essential Topics ! 126: volume, or this manual won't make much sense to you. Reading this ! 127: Special Topics volume is optional. ! 128: ! 129: ! 130: ! 131: Special Topics ! 132: =============== ! 133: ! 134: ! 135: Selecting Keys via Key ID ! 136: ------------------------- ! 137: ! 138: In all commands that let the user type a user ID or fragment of a ! 139: user ID to select a key, the hexadecimal key ID may be used instead. ! 140: Just use the key ID, with a prefix of "0x", in place of the user ID. ! 141: For example: ! 142: ! 143: pgp -kv 0x67F7 ! 144: ! 145: This would display all keys that had 67F7 as part of their key IDs. ! 146: ! 147: This feature is particularly useful if you have two different keys ! 148: from the same person, with the same user ID. You can unambiguously ! 149: pick which key you want by specifying the key ID. ! 150: ! 151: ! 152: Separating Signatures from Messages ! 153: ----------------------------------- ! 154: ! 155: Normally, signature certificates are physically attached to the text ! 156: they sign. This makes it convenient in simple cases to check ! 157: signatures. It is desirable in some circumstances to have signature ! 158: certificates stored separately from the messages they sign. It is ! 159: possible to generate signature certificates that are detached from ! 160: the text they sign. To do this, combine the 'b' (break) option with ! 161: the 's' (sign) option. For example: ! 162: ! 163: pgp -sb letter.txt ! 164: ! 165: This example produces an isolated signature certificate in a file ! 166: called "letter.sig". The contents of letter.txt are not appended to ! 167: the signature certificate. ! 168: ! 169: After creating the signature certificate file (letter.sig in the ! 170: above example), send it along with the original text file to the ! 171: recipient. The recipient must have both files to check the signature ! 172: integrity. When the recipient attempts to process the signature ! 173: file, PGP notices that there is no text in the same file with the ! 174: signature and prompts the user for the filename of the text. Only ! 175: then can PGP properly check the signature integrity. If the ! 176: recipient knows in advance that the signature is detached from the ! 177: text file, she can specify both filenames on the command line: ! 178: ! 179: pgp letter.sig letter.txt ! 180: or: pgp letter letter.txt ! 181: ! 182: PGP will not have to prompt for the text file name in this case. ! 183: ! 184: A detached signature certificate is useful if you want to keep the ! 185: signature certificate in a separate certificate log. A detached ! 186: signature of an executable program is also useful for detecting a ! 187: subsequent virus infection. It is also useful if more than one party ! 188: must sign a document such as a legal contract, without nesting ! 189: signatures. Each person's signature is independent. ! 190: ! 191: If you receive a ciphertext file that has the signature certificate ! 192: glued to the message, you can still pry the signature certificate ! 193: away from the message during the decryption. You can do this with ! 194: the -b option during decrypt, like so: ! 195: ! 196: pgp -b letter ! 197: ! 198: This decrypts the letter.pgp file and if there is a signature in it, ! 199: PGP checks the signature and detaches it from the rest of the ! 200: message, storing it in the file letter.sig. ! 201: ! 202: ! 203: Decrypting the Message and Leaving the Signature on it ! 204: ------------------------------------------------------ ! 205: ! 206: Usually, you want PGP to completely unravel a ciphertext file, ! 207: decrypting it and checking the nested signature if there is one, ! 208: peeling away the layers until you are left with only the original ! 209: plaintext file. ! 210: ! 211: But sometimes you want to decrypt an encrypted file, and leave the ! 212: inner signature still attached, so that you are left with a decrypted ! 213: signed message. This may be useful if you want to send a copy of a ! 214: signed document to a third party, perhaps re-enciphering it. For ! 215: example, suppose you get a message signed by Charlie, encrypted to ! 216: you. You want to decrypt it, and, leaving Charlie's signature on it, ! 217: you want to send it to Alice, perhaps re-enciphering it with Alice's ! 218: public key. No problem. PGP can handle that. ! 219: ! 220: To simply decrypt a message and leave the signature on it intact, ! 221: type: ! 222: ! 223: pgp -d letter ! 224: ! 225: This decrypts letter.pgp, and if there is an inner signature, it is ! 226: left intact with the decrypted plaintext in the output file. ! 227: ! 228: Now you can archive it, or maybe re-encrypt it and send it to someone ! 229: else. ! 230: ! 231: ! 232: ! 233: Sending ASCII Text Files Across Different Machine Environments ! 234: -------------------------------------------------------------- ! 235: ! 236: You may use PGP to encrypt any kind of plaintext file, binary 8-bit ! 237: data or ASCII text. Probably the most common usage of PGP will be for ! 238: E-mail, when the plaintext is ASCII text. ! 239: ! 240: ASCII text is sometimes represented differently on different ! 241: machines. For example, on an MSDOS system, all lines of ASCII text ! 242: are terminated with a carriage return followed by a linefeed. On a ! 243: Unix system, all lines end with just a linefeed. On a Macintosh, all ! 244: lines end with just a carriage return. This is a sad fact of life. ! 245: ! 246: Normal unencrypted ASCII text messages are often automatically ! 247: translated to some common "canonical" form when they are transmitted ! 248: from one machine to another. Canonical text has a carriage return ! 249: and a linefeed at the end of each line of text. For example, the ! 250: popular KERMIT communication protocol can convert text to canonical ! 251: form when transmitting it to another system. This gets converted ! 252: back to local text line terminators by the receiving KERMIT. This ! 253: makes it easy to share text files across different systems. ! 254: ! 255: But encrypted text cannot be automatically converted by a ! 256: communication protocol, because the plaintext is hidden by ! 257: encipherment. To remedy this inconvenience, PGP lets you specify ! 258: that the plaintext should be treated as ASCII text (not binary data) ! 259: and should be converted to canonical text form before it gets ! 260: encrypted. At the receiving end, the decrypted plaintext is ! 261: automatically converted back to whatever text form is appropriate for ! 262: the local environment. ! 263: ! 264: To make PGP assume the plaintext is text that should be converted to ! 265: canonical text before encryption, just add the "t" option when ! 266: encrypting or signing a message, like so: ! 267: ! 268: pgp -et message.txt her_userid ! 269: ! 270: This mode is automatically turned off if PGP detects that the ! 271: plaintext file contains what it thinks is non-text binary data. ! 272: ! 273: For PGP users that use non-English 8-bit character sets, when PGP ! 274: converts text to canonical form, it may convert data from the local ! 275: character set into the LATIN1 (ISO 8859-1 Latin Alphabet 1) character ! 276: set, depending on the setting of the CHARSET parameter in the PGP ! 277: configuration file. LATIN1 is a superset of ASCII, with extra ! 278: characters added for many European languages. ! 279: ! 280: ! 281: ! 282: Leaving No Traces of Plaintext on the Disk ! 283: ------------------------------------------ ! 284: ! 285: After PGP makes a ciphertext file for you, you can have PGP ! 286: automatically overwrite the plaintext file and delete it, leaving no ! 287: trace of plaintext on the disk so that no one can recover it later ! 288: using a disk block scanning utility. This is useful if the plaintext ! 289: file contains sensitive information that you don't want to keep ! 290: around. ! 291: ! 292: To wipe out the plaintext file after producing the ciphertext file, ! 293: just add the "w" (wipe) option when encrypting or signing a message, ! 294: like so: ! 295: ! 296: pgp -esw message.txt her_userid ! 297: ! 298: This example creates the ciphertext file "message.pgp", and the ! 299: plaintext file "message.txt" is destroyed beyond recovery. ! 300: ! 301: Obviously, you should be careful with this option. Also note that ! 302: this will not wipe out any fragments of plaintext that your word ! 303: processor might have created on the disk while you were editing the ! 304: message before running PGP. Most word processors create backup ! 305: files, scratch files, or both. Also, it overwrites the file only ! 306: once, which is enough to thwart conventional disk recovery efforts, ! 307: but not enough to withstand a determined and sophisticated effort to ! 308: recover the faint magnetic traces of the data using special disk ! 309: recovery hardware. ! 310: ! 311: ! 312: ! 313: Displaying Decrypted Plaintext on Your Screen ! 314: --------------------------------------------- ! 315: ! 316: To view the decrypted plaintext output on your screen (like the ! 317: Unix-style "more" command), without writing it to a file, use the -m ! 318: (more) option while decrypting: ! 319: ! 320: pgp -m ciphertextfile ! 321: ! 322: This displays the decrypted plaintext display on your screen one ! 323: screenful at a time. ! 324: ! 325: ! 326: ! 327: Making a Message For Her Eyes Only ! 328: ---------------------------------- ! 329: ! 330: To specify that the recipient's decrypted plaintext will be shown ! 331: ONLY on her screen and cannot be saved to disk, add the -m option: ! 332: ! 333: pgp -sem message.txt her_userid ! 334: ! 335: Later, when the recipient decrypts the ciphertext with her secret key ! 336: and pass phrase, the plaintext will be displayed on her screen but ! 337: will not be saved to disk. The text will be displayed as it would if ! 338: she used the Unix "more" command, one screenful at a time. If she ! 339: wants to read the message again, she will have to decrypt the ! 340: ciphertext again. ! 341: ! 342: This feature is the safest way for you to prevent your sensitive ! 343: message from being inadvertently left on the recipient's disk. This ! 344: feature was added at the request of a user who wanted to send ! 345: intimate messages to his lover, but was afraid she might accidentally ! 346: leave the decrypted messages on her husband's computer. ! 347: ! 348: ! 349: ! 350: Preserving the Original Plaintext Filename ! 351: ------------------------------------------ ! 352: ! 353: Normally, PGP names the decrypted plaintext output file with a name ! 354: similar to the input ciphertext filename, but dropping the ! 355: extension. Or, you can override that convention by specifying an ! 356: output plaintext filename on the command line with the -o option. ! 357: For most E-mail, this is a reasonable way to name the plaintext file, ! 358: because you get to decide its name when you decipher it, and your ! 359: typical E-mail messages often come from useless original plaintext ! 360: filenames like "to_phil.txt". ! 361: ! 362: But when PGP encrypts a plaintext file, it always saves the original ! 363: filename and attaches it to the plaintext before it compresses and ! 364: encrypts the plaintext. Normally, this hidden original filename is ! 365: discarded by PGP when it decrypts, but you can tell PGP you want to ! 366: preserve the original plaintext filename and use it as the name of ! 367: the decrypted plaintext output file. This is useful if PGP is used ! 368: to on files whose names are important to preserve. ! 369: ! 370: To recover the original plaintext filename while decrypting, add ! 371: the -p option, like so: ! 372: ! 373: pgp -p ciphertextfile ! 374: ! 375: I usually don't use this option, because if I did, about half of my ! 376: incoming E-mail would decrypt to the same plaintext filenames of ! 377: "to_phil.txt" or "prz.txt". ! 378: ! 379: ! 380: ! 381: Editing Your User ID or Pass Phrase ! 382: ----------------------------------- ! 383: ! 384: Sometimes you may need to change your pass phrase, perhaps because ! 385: someone looked over your shoulder while you typed it in. ! 386: ! 387: Or you may need to change your user ID, because you got married and ! 388: changed your name, or maybe you changed your E-mail address. Or ! 389: maybe you want to add a second or third user ID to your key, because ! 390: you may be known by more than one name or E-mail address or job ! 391: title. PGP lets you attach more than one user ID to your key, any ! 392: one of which may be used to look up your key on the key ring. ! 393: ! 394: To edit your userid or pass phrase for your secret key: ! 395: ! 396: pgp -ke userid [keyring] ! 397: ! 398: PGP prompts you for a new user ID or a new pass phrase. ! 399: ! 400: ! 401: ! 402: Editing the Trust Parameters for a Public Key ! 403: --------------------------------------------- ! 404: ! 405: Sometimes you need to alter the trust parameters for a public key on ! 406: your public key ring. For a discussion on what these trust ! 407: parameters mean, see the section "How Does PGP Keep Track of Which ! 408: Keys are Valid?" in the Essential Topics volume of the PGP User's ! 409: Guide. ! 410: ! 411: To edit the trust parameters for a public key: ! 412: ! 413: pgp -ke userid [keyring] ! 414: ! 415: ! 416: ! 417: Checking If Everything is OK on Your Public Key Ring ! 418: ---------------------------------------------------- ! 419: ! 420: Normally, PGP automatically checks any new keys or signatures on your ! 421: public key ring and updates all the trust parameters and validity ! 422: scores. In theory, it keeps all the key validity status information ! 423: up to date as material is added to or deleted from your public key ! 424: ring. But perhaps you may want to explicitly force PGP to perform a ! 425: comprehensive analysis of your public key ring, checking all the ! 426: certifying signatures, checking the trust parameters, updating all ! 427: the validity scores, and checking your own ultimately-trusted key ! 428: against a backup copy on a write-protected floppy disk. It may be a ! 429: good idea to do this hygienic maintenance periodically to make sure ! 430: nothing is wrong with your public key ring. To force PGP to perform ! 431: a full analysis of your public key ring, use the -kc (key ring check) ! 432: command: ! 433: ! 434: pgp -kc ! 435: ! 436: You can also make PGP check all the signatures for just a single ! 437: selected public key by: ! 438: ! 439: pgp -kc userid [keyring] ! 440: ! 441: For further information on how the backup copy of your own key is ! 442: checked, see the description of the BAKRING parameter in the ! 443: configuration file section of this manual. ! 444: ! 445: ! 446: ! 447: Verifying a Public Key Over the Phone ! 448: ------------------------------------- ! 449: ! 450: If you get a public key from someone that is not certified by anyone ! 451: you trust, how can you tell if it's really their key? The best way ! 452: to verify an uncertified key is to verify it over some independent ! 453: channel other than the one you received the key through. One ! 454: convenient way to tell, if you know this person and would recognize ! 455: them on the phone, is to call them and verify their key over the ! 456: telephone. Rather than reading their whole tiresome (ASCII-armored) ! 457: key to them over the phone, you can just read their key's ! 458: "fingerprint" to them. To see this fingerprint, use the -kvc ! 459: command: ! 460: ! 461: pgp -kvc userid [keyring] ! 462: ! 463: This will display the key with the 16-byte digest of the public key ! 464: components. Read this 16-byte fingerprint to the key's owner on the ! 465: phone, while she checks it against her own, using the same -kvc ! 466: command at her end. ! 467: ! 468: You can both verify each other's keys this way, and then you can sign ! 469: each other's keys with confidence. This is a safe and convenient way ! 470: to get the key trust network started for your circle of friends. ! 471: ! 472: ! 473: ! 474: Using PGP as a Unix-style Filter ! 475: -------------------------------- ! 476: ! 477: Unix fans are accustomed to using Unix "pipes" to make two ! 478: applications work together. The output of one application can be ! 479: directly fed through a pipe to be read as input to another ! 480: application. For this to work, the applications must be capable of ! 481: reading the raw material from "standard input" and writing the ! 482: finished output to "standard output". PGP can operate in this mode. ! 483: If you don't understand what this means, then you probably don't need ! 484: this feature. ! 485: ! 486: To use a Unix-style filter mode, reading from standard input and ! 487: writing to standard output, add the -f option, like so: ! 488: ! 489: pgp -feast her_userid <inputfile >outputfile ! 490: ! 491: This feature makes it easier to make PGP work with electronic mail ! 492: applications. ! 493: ! 494: When using PGP in filter mode to decrypt a ciphertext file, you may ! 495: find it useful to use the PGPPASS environmental variable to hold the ! 496: pass phrase, so that you won't be prompted for it. The PGPPASS ! 497: feature is explained below. ! 498: ! 499: ! 500: ! 501: Suppressing Unneccessary Questions: BATCHMODE ! 502: ---------------------------------------------- ! 503: ! 504: With the BATCHMODE flag enabled on the command line, PGP will not ask ! 505: any unneccessary questions or prompt for alternate filenames. Here ! 506: is an example of how to set this flag: ! 507: ! 508: pgp +batchmode cipherfile ! 509: ! 510: This is useful for running PGP non-interactively from Unix shell ! 511: scripts or MSDOS batch files. Some key management commands still ! 512: need user interaction even when BATCHMODE is on, so shell scripts may ! 513: need to avoid them. ! 514: ! 515: BATCHMODE may also be enabled to check the validity of a signature on ! 516: a file. If there was no signature on the file, the exit code is 1. ! 517: If it had a signature that was good, the exit code is 0. ! 518: ! 519: ! 520: Force "Yes" Answer to Confirmation Questions: FORCE ! 521: ---------------------------------------------------- ! 522: ! 523: This command-line flag makes PGP assume "yes" for the user response ! 524: to the confirmation request to overwrite an existing file, or when ! 525: removing a key from the keyring via the -kr command. Here is an ! 526: example of how to set this flag: ! 527: ! 528: pgp +force cipherfile ! 529: or: ! 530: pgp -kr +force Smith ! 531: ! 532: This feature is useful for running PGP non-interactively from a Unix ! 533: shell script or MSDOS batch file. ! 534: ! 535: ! 536: ! 537: PGP Returns Exit Status to the Shell ! 538: ------------------------------------ ! 539: ! 540: To facilitate running PGP in "batch" mode, such as from an MSDOS ! 541: ".bat" file or from a Unix shell script, PGP returns an error exit ! 542: status to the shell. An exit status code of zero means normal exit, ! 543: while a nonzero exit status indicates some kind of error occurred. ! 544: Different error exit conditions return different exit status codes to ! 545: the shell. ! 546: ! 547: ! 548: ! 549: Environmental Variable for Pass Phrase ! 550: -------------------------------------- ! 551: ! 552: Normally, PGP prompts the user to type a pass phrase whenever PGP ! 553: needs a pass phrase to unlock a secret key. But it is possible to ! 554: store the pass phrase in an environmental variable from your ! 555: operating system's command shell. The environmental variable PGPPASS ! 556: can be used to hold the pass phrase that PGP will attempt to use ! 557: first. If the pass phrase stored in PGPPASS is incorrect, PGP ! 558: recovers by prompting the user for the correct pass phrase. ! 559: ! 560: For example, on MSDOS, the shell command: ! 561: ! 562: SET PGPPASS=zaphod beeblebrox for president ! 563: ! 564: would eliminate the prompt for the pass phrase if the pass phrase ! 565: were indeed "zaphod beeblebrox for president". ! 566: ! 567: This dangerous feature makes your life more convenient if you have to ! 568: regularly deal with a large number of incoming messages addressed to ! 569: your secret key, by eliminating the need for you to repeatedly type ! 570: in your pass phrase every time you run PGP. ! 571: ! 572: I added this feature because of popular demand. However, this is a ! 573: somewhat dangerous feature, because it keeps your precious pass ! 574: phrase stored somewhere other than just in your brain. Even worse, ! 575: if you are particularly reckless, it may even be stored on a disk on ! 576: the same computer as your secret key. It would be particularly ! 577: dangerous and stupid if you were to install this command in a batch ! 578: or script file, such as the MSDOS AUTOEXEC.BAT file. Someone could ! 579: come along on your lunch hour and steal both your secret key ring and ! 580: the file containing your pass phrase. ! 581: ! 582: I can't emphasize the importance of this risk enough. If you are ! 583: contemplating using this feature, be sure to read the sections ! 584: "Exposure on Multi-user Systems" and "How to Protect Secret Keys from ! 585: Disclosure" in this volume and in the Essential Topics volume of the ! 586: PGP User's Guide. ! 587: ! 588: If you must use this feature, the safest way to do it would be to ! 589: just manually type in the shell command to set PGPPASS every time you ! 590: boot your machine to start using PGP, and then erase it or turn off ! 591: your machine when you are done. And you should definitely never do ! 592: it in an environment where someone else may have access to your ! 593: machine. Someone could come along and simply ask your computer to ! 594: display the contents of PGPPASS. ! 595: ! 596: ! 597: ! 598: Setting Configuration Parameters: CONFIG.TXT ! 599: ============================================ ! 600: ! 601: PGP has a number of user-settable parameters that can be defined in a ! 602: special configuration text file called "config.txt", in the directory ! 603: pointed to by the shell environmental variable PGPPATH. Having a ! 604: configuration file enables the user to define various flags and ! 605: parameters for PGP without the burden of having to always define ! 606: these parameters in the PGP command line. ! 607: ! 608: Configuration parameters may be assigned integer values, character ! 609: string values, or on/off values, depending on what kind of ! 610: configuration parameter it is. A sample configuration file is ! 611: provided with PGP, so you can see some examples. ! 612: ! 613: In the configuration file, blank lines are ignored, as is anything ! 614: following the '#' comment character. Keywords are not ! 615: case-sensitive. ! 616: ! 617: Here is a short sample fragment of a typical configuration file: ! 618: ! 619: # TMP is the directory for PGP scratch files, such as a RAM disk. ! 620: TMP = "e:\" # Can be overridden by environment variable TMP. ! 621: Armor = on # Use -a flag for ASCII armor whenever applicable. ! 622: # CERT_DEPTH is how deeply introducers may introduce introducers. ! 623: cert_depth = 3 ! 624: ! 625: If some configuration parameters are not defined in the configuration ! 626: file, or if there is no configuration file, or if PGP can't find the ! 627: configuration file, the values for the configuration parameters ! 628: default to some reasonable value. ! 629: ! 630: Note that it is also possible to set these same configuration ! 631: parameters directly from the PGP command line, by preceding the ! 632: parameter setting with a "+" character. For example, the following ! 633: two PGP commands produce the same effect: ! 634: ! 635: pgp -e +armor=on message.txt smith ! 636: or: pgp -ea message.txt smith ! 637: ! 638: ! 639: The following is a summary of the various parameters than may be ! 640: defined in the configuration file. ! 641: ! 642: ! 643: TMP - Directory Pathname for Temporary Files ! 644: -------------------------------------------- ! 645: ! 646: Default setting: TMP = "" ! 647: ! 648: The configuration parameter TMP specifies what directory to use for ! 649: PGP's temporary scratch files. The best place to put them is on a ! 650: RAM disk, if you have one. That speeds things up quite a bit, and ! 651: increases security somewhat. If TMP is undefined, the temporary ! 652: files go in the current directory. If the shell environmental ! 653: variable TMP is defined, PGP instead uses that to specify where the ! 654: temporary files should go. ! 655: ! 656: ! 657: LANGUAGE - Foreign Language Selector ! 658: ------------------------------------ ! 659: ! 660: Default setting: LANGUAGE = "en" ! 661: ! 662: PGP displays various prompts, warning messages, and advisories to the ! 663: user on the screen. For example, messages such as "File not found.", ! 664: or "Please enter your pass phrase:". These messages are normally in ! 665: English. But it is possible to get PGP to display its messages to ! 666: the user in other languages, without having to modify the PGP ! 667: executable program. ! 668: ! 669: A number of people in various countries have translated all of PGP's ! 670: display messages, warnings, and prompts into their native languages. ! 671: These hundreds of translated message strings have been placed in a ! 672: special text file called "language.txt", distributed with the PGP ! 673: release. The messages are stored in this file in English, Spanish, ! 674: Dutch, German, French, Italian, Russian, Latvian, and Lithuanian. ! 675: Other languages may be added later. ! 676: ! 677: The configuration parameter LANGUAGE specifies what language to ! 678: display these messages in. LANGUAGE may be set to "en" for English, ! 679: "es" for Spanish, "de" for German, "nl" for Dutch, "fr" for French, ! 680: "it" for Italian, "ru" for Russian, "lt3" for Lithuanian, "lv" for ! 681: Latvian, "esp" for Esperanto. For example, if this line appeared in ! 682: the configuration file: ! 683: ! 684: LANGUAGE = "fr" ! 685: ! 686: PGP would select French as the language for its display messages. ! 687: The default setting is English. ! 688: ! 689: When PGP needs to display a message to the user, it looks in the ! 690: "language.txt" file for the equivalent message string in the selected ! 691: foreign language and displays that translated message to the user. ! 692: If PGP can't find the language string file, or if the selected ! 693: language is not in the file, or if that one phrase is not translated ! 694: into the selected language in the file, or if that phrase is missing ! 695: entirely from the file, PGP displays the message in English. ! 696: ! 697: To conserve disk space, most foreign translations are not included ! 698: in the standard PGP release package, but are available separately. ! 699: ! 700: ! 701: MYNAME - Default User ID for Making Signatures ! 702: ---------------------------------------------- ! 703: ! 704: Default setting: MYNAME = "" ! 705: ! 706: The configuration parameter MYNAME specifies the default user ID to ! 707: use to select the secret key for making signatures. If MYNAME is not ! 708: defined, the most recent secret key you installed on your secret key ! 709: ring will be used. The user may also override this setting by ! 710: specifying a user ID on the PGP command line with the -u option. ! 711: ! 712: ! 713: TEXTMODE - Assuming Plaintext is a Text File ! 714: -------------------------------------------- ! 715: ! 716: Default setting: TEXTMODE = off ! 717: ! 718: The configuration parameter TEXTMODE is equivalent to the -t command ! 719: line option. If enabled, it causes PGP to assume the plaintext is a ! 720: text file, not a binary file, and converts it to "canonical text" ! 721: before encrypting it. Canonical text has a carriage return and a ! 722: linefeed at the end of each line of text. ! 723: ! 724: This mode will be automatically turned off if PGP detects that the ! 725: plaintext file contains what it thinks is non-text binary data. ! 726: ! 727: For VAX/VMS systems, the current version of PGP defaults TEXTMODE=ON. ! 728: ! 729: For further details, see the section "Sending ASCII Text Files Across ! 730: Different Machine Environments". ! 731: ! 732: ! 733: CHARSET - Specifies Local Character Set for Text Files ! 734: ------------------------------------------------------ ! 735: ! 736: Default setting: CHARSET = NOCONV ! 737: ! 738: Because PGP must process messages in many non-English languages with ! 739: non-ASCII character sets, you may have a need to tell PGP what local ! 740: character set your machine uses. This determines what character ! 741: conversions are performed when converting plaintext files to and from ! 742: canonical text format. This is only a concern if you are in a ! 743: non-English non-ASCII environment. ! 744: ! 745: The configuration parameter CHARSET selects the local character set. ! 746: The choices are NOCONV (no conversion), LATIN1 (ISO 8859-1 Latin ! 747: Alphabet 1), KOI8 (used by most Russian Unix systems), ALT_CODES ! 748: (used by Russian MSDOS systems), ASCII, and CP850 (used by most ! 749: western European languages on standard MSDOS PCs). ! 750: ! 751: LATIN1 is the internal representation used by PGP for canonical text, ! 752: so if you select LATIN1, no conversion is done. Note also that PGP ! 753: treats KOI8 as LATIN1, even though it is a completely different ! 754: character set (Russian), because trying to convert KOI8 to either ! 755: LATIN1 or CP850 would be futile anyway. This means that setting ! 756: CHARSET to NOCONV, LATIN1, or KOI8 are all equivalent to PGP. ! 757: ! 758: If you use MSDOS and expect to send or receive traffic in western ! 759: European languages, set CHARSET = "CP850". This will make PGP ! 760: convert incoming canonical text messages from LATIN1 to CP850 after ! 761: decryption. If you use the -t (textmode) option to convert to ! 762: canonical text, PGP will convert your CP850 text to LATIN1 before ! 763: encrypting it. ! 764: ! 765: For further details, see the section "Sending ASCII Text Files Across ! 766: Different Machine Environments". ! 767: ! 768: ! 769: ARMOR - Enable ASCII Armor Output ! 770: --------------------------------- ! 771: ! 772: Default setting: ARMOR = off ! 773: ! 774: The configuration parameter ARMOR is equivalent to the -a command ! 775: line option. If enabled, it causes PGP to emit ciphertext or keys in ! 776: ASCII Radix-64 format suitable for transporting through E-mail ! 777: channels. Output files are named with the ".asc" extension. ! 778: ! 779: If you tend to use PGP mostly for E-mail, it may be a good idea to ! 780: enable this parameter. ! 781: ! 782: For further details, see the section "Sending Ciphertext Through ! 783: E-mail Channels: Radix-64 Format" in the Essential Topics volume. ! 784: ! 785: ! 786: ARMORLINES - Size of ASCII Armor Multipart Files ! 787: ------------------------------------------------ ! 788: ! 789: Default setting: ARMORLINES = 720 ! 790: ! 791: When PGP creates a very large ".asc" radix-64 file for sending ! 792: ciphertext or keys through the E-mail, it breaks the file up into ! 793: separate chunks small enough to send through Internet mail ! 794: utilities. Normally, Internet mailers prohibit files larger than ! 795: about 50000 bytes, which means that if we restrict the number of ! 796: lines to about 720, we'll be well within the limit. The file chunks ! 797: are named with suffixes ".as1", ".as2", ".as3", ... ! 798: ! 799: The configuration parameter ARMORLINES specifies the maximum number ! 800: of lines to make each chunk in a multipart ".asc" file sequence. If ! 801: you set it to zero, PGP will not break up the file into chunks. ! 802: ! 803: Fidonet email files usually have an upper limit of about 32K bytes, ! 804: so 450 lines would be appropriate for Fidonet environments. ! 805: ! 806: For further details, see the section "Sending Ciphertext Through ! 807: E-mail Channels: Radix-64 Format" in the Essential Topics volume. ! 808: ! 809: ! 810: KEEPBINARY - Keep Binary Ciphertext Files After Decrypting ! 811: ---------------------------------------------------------- ! 812: ! 813: Default setting: KEEPBINARY = off ! 814: ! 815: When PGP reads a ".asc" file, it recognizes that the file is in ! 816: radix-64 format and will convert it back to binary before processing ! 817: as it normally does, producing as a by-product a ".pgp" ciphertext ! 818: file in binary form. After further processing to decrypt the ".pgp" ! 819: file, the final output file will be in normal plaintext form. ! 820: ! 821: You may want to delete the binary ".pgp" intermediate file, or you ! 822: may want PGP to delete it for you automatically. You can still rerun ! 823: PGP on the original ".asc" file. ! 824: ! 825: The configuration parameter KEEPBINARY enables or disables keeping ! 826: the intermediate ".pgp" file during decryption. ! 827: ! 828: For further details, see the section "Sending Ciphertext Through ! 829: E-mail Channels: Radix-64 Format" in the Essential Topics volume. ! 830: ! 831: ! 832: COMPRESS - Enable Compression ! 833: ----------------------------- ! 834: ! 835: Default setting: COMPRESS = on ! 836: ! 837: The configuration parameter COMPRESS enables or disables data ! 838: compression before encryption. It is used mainly for debugging PGP. ! 839: Normally, PGP attempts to compress the plaintext before it encrypts ! 840: it. Generally, you should leave this alone and let PGP attempt to ! 841: compress the plaintext. ! 842: ! 843: ! 844: COMPLETES_NEEDED - Number of Completely Trusted Introducers Needed ! 845: ------------------------------------------------------------------ ! 846: ! 847: Default setting: COMPLETES_NEEDED = 1 ! 848: ! 849: The configuration parameter COMPLETES_NEEDED specifies the minimum ! 850: number of completely trusted introducers required to fully certify a ! 851: public key on your public key ring. This gives you a way of tuning ! 852: PGP's skepticism. ! 853: ! 854: For further details, see the section "How Does PGP Keep Track of ! 855: Which Keys are Valid?" in the Essential Topics volume. ! 856: ! 857: ! 858: MARGINALS_NEEDED - Number of Marginally Trusted Introducers Needed ! 859: ------------------------------------------------------------------ ! 860: ! 861: Default setting: MARGINALS_NEEDED = 2 ! 862: ! 863: The configuration parameter MARGINALS_NEEDED specifies the minimum ! 864: number of marginally trusted introducers required to fully certify a ! 865: public key on your public key ring. This gives you a way of tuning ! 866: PGP's skepticism. ! 867: ! 868: For further details, see the section "How Does PGP Keep Track of ! 869: Which Keys are Valid?" in the Essential Topics volume. ! 870: ! 871: ! 872: CERT_DEPTH - How Deep May Introducers Be Nested ! 873: ----------------------------------------------- ! 874: ! 875: Default setting: CERT_DEPTH = 4 ! 876: ! 877: The configuration parameter CERT_DEPTH specifies how many levels deep ! 878: you may nest introducers to certify other introducers to certify ! 879: public keys on your public key ring. For example, If CERT_DEPTH is ! 880: set to 1, there may only be one layer of introducers below your own ! 881: ultimately-trusted key. If that were the case, you would be required ! 882: to directly certify the public keys of all trusted introducers on ! 883: your key ring. If you set CERT_DEPTH to 0, you could have no ! 884: introducers at all, and you would have to directly certify each and ! 885: every key on your public key ring in order to use it. The minimum ! 886: CERT_DEPTH is 0, the maximum is 8. ! 887: ! 888: For further details, see the section "How Does PGP Keep Track of ! 889: Which Keys are Valid?" in the Essential Topics volume. ! 890: ! 891: ! 892: BAKRING - Filename for Backup Secret Keyring ! 893: -------------------------------------------- ! 894: ! 895: Default setting: BAKRING = "" ! 896: ! 897: All of the key certification that PGP does on your public key ring ! 898: ultimately depends on your own ultimately-trusted public key (or ! 899: keys). To detect any tampering of your public key ring, PGP must ! 900: check that your own key has not been tampered with. To do this, PGP ! 901: must compare your public key against a backup copy of your secret key ! 902: on some tamper-resistant media, such as a write-protected floppy ! 903: disk. A secret key contains all the information that your public key ! 904: has, plus some secret components. This means PGP can check your ! 905: public key against a backup copy of your secret key. ! 906: ! 907: The configuration parameter BAKRING specifies what pathname to use ! 908: for PGP's trusted backup copy of your secret key ring. On MSDOS, you ! 909: could set it to "a:\secring.pgp" to point it at a write-protected ! 910: backup copy of your secret key ring on your floppy drive. This check ! 911: is performed only when you execute the PGP -kc option to check your ! 912: whole public key ring. ! 913: ! 914: If BAKRING is not defined, PGP will not check your own key against ! 915: any backup copy. ! 916: ! 917: For further details, see the sections "How to Protect Public Keys ! 918: from Tampering" and "How Does PGP Keep Track of Which Keys are ! 919: Valid?" in the Essential Topics volume. ! 920: ! 921: ! 922: PAGER - Selects Shell Command to Display Plaintext Output ! 923: --------------------------------------------------------- ! 924: ! 925: Default setting: PAGER = "" ! 926: ! 927: PGP lets you view the decrypted plaintext output on your screen (like ! 928: the Unix-style "more" command), without writing it to a file, if you ! 929: use the -m (more) option while decrypting. This displays the ! 930: decrypted plaintext display on your screen one screenful at a time. ! 931: ! 932: If you prefer to use a fancier page display utility, rather than ! 933: PGP's built-in one, you can specify the name of a shell command that ! 934: PGP will invoke to display your plaintext output file. The ! 935: configuration parameter PAGER specifies the shell command to invoke ! 936: to display the file. For example, on MSDOS systems, you might want ! 937: to use the popular shareware program "list.com" to display your ! 938: plaintext message. Assuming you have a copy of "list.com", you may ! 939: set PAGER accordingly: ! 940: ! 941: PAGER = "list" ! 942: ! 943: However, if the sender specified that this file is for your eyes ! 944: only, and may not be written to disk, PGP always uses its own ! 945: built-in display function. ! 946: ! 947: For further details, see the section "Displaying Decrypted Plaintext ! 948: on Your Screen". ! 949: ! 950: ! 951: SHOWPASS - Echo Pass Phrase to User ! 952: ----------------------------------- ! 953: ! 954: Default setting: SHOWPASS = off ! 955: ! 956: Normally, PGP does not let you see your pass phrase as you type it ! 957: in. This makes it harder for someone to look over your shoulder ! 958: while you type and learn your pass phrase. But some typing-impaired ! 959: people have problems typing their pass phrase without seeing what ! 960: they are typing, and they may be typing in the privacy of their own ! 961: homes. So they asked if PGP can be configured to let them see what ! 962: they type when they type in their pass phrase. ! 963: ! 964: The configuration parameter SHOWPASS enables PGP to echo your typing ! 965: during pass phrase entry. ! 966: ! 967: ! 968: TZFIX - Timezone Adjustment ! 969: --------------------------- ! 970: ! 971: Default setting: TZFIX = 0 ! 972: ! 973: PGP provides timestamps for keys and signature certificates in ! 974: Greenwich Mean Time (GMT), or Coordinated Universal Time (UTC), which ! 975: means the same thing for our purposes. When PGP asks the system for ! 976: the time of day, the system is supposed to provide it in GMT. ! 977: ! 978: But sometimes, because of improperly configured MSDOS systems, the ! 979: system time is returned in US Pacific Standard Time time plus 8 ! 980: hours. Sounds weird, doesn't it? Perhaps because of some sort of US ! 981: west-coast jingoism, MSDOS presumes local time is US Pacific time, ! 982: and pre-corrects Pacific time to GMT. This adversely affects the ! 983: behavior of the internal MSDOS GMT time function that PGP calls. ! 984: However, if your MSDOS environmental variable TZ is already properly ! 985: defined for your timezone, this corrects the misconception MSDOS has ! 986: that the whole world lives on the US west coast. ! 987: ! 988: The configuration parameter TZFIX specifies the number of hours to ! 989: add to the system time function to get GMT, for GMT timestamps on ! 990: keys and signatures. If the MSDOS environmental variable TZ is ! 991: defined properly, you can leave TZFIX=0. Unix systems usually ! 992: shouldn't need to worry about setting TZFIX at all. But if you are ! 993: using some other obscure operating system that doesn't know about ! 994: GMT, you may have to use TZFIX to adjust the system time to GMT. ! 995: ! 996: On MSDOS systems that do not have TZ defined in the environment, you ! 997: should make TZFIX=0 for California, -1 for Colorado, -2 for Chicago, ! 998: -3 for New York, -8 for London, -9 for Amsterdam. In the summer, ! 999: TZFIX should be manually decremented from these values. What a mess. ! 1000: ! 1001: It would be much cleaner to set your MSDOS environmental variable TZ ! 1002: in your AUTOEXEC.BAT file, and not use the TZFIX correction. Then ! 1003: MSDOS gives you good GMT timestamps, and will handle daylight savings ! 1004: time adjustments for you. Here are some sample lines to insert into ! 1005: AUTOEXEC.BAT, depending on your time zone: ! 1006: ! 1007: For Los Angeles: SET TZ=PST8PDT ! 1008: For Denver: SET TZ=MST7MDT ! 1009: For Arizona: SET TZ=MST7 ! 1010: (Arizona never uses daylight savings time) ! 1011: For Chicago: SET TZ=CST6CDT ! 1012: For New York: SET TZ=EST5EDT ! 1013: For London: SET TZ=GMT0BST ! 1014: For Amsterdam: SET TZ=MET-1DST ! 1015: For Moscow: SET TZ=MSK-3MSD ! 1016: For Aukland: SET TZ=NZT-13 ! 1017: ! 1018: ! 1019: CLEARSIG - Enable Signed Messages to be Encapsulated as Clear Text ! 1020: ------------------------------------------------------------------ ! 1021: ! 1022: Default setting: CLEARSIG = off ! 1023: ! 1024: Normally, unencrypted PGP signed messages have a signature ! 1025: certificate prepended in binary form. To send this through a 7-bit ! 1026: E-mail channel, radix-64 ASCII armor is applied (see the ARMOR ! 1027: parameter), rendering the message unreadable to casual human eyes, ! 1028: even though the message is not actually encrypted. The recipient ! 1029: must use PGP to strip the armor off before reading the message. ! 1030: ! 1031: If the original plaintext message is in text (not binary) form, there ! 1032: is a way to send it through an E-mail channel in such a way that the ! 1033: ASCII armor is applied only to the binary signature certificate, but ! 1034: not to the plaintext message. This makes it possible to read the ! 1035: signed message with human eyes, without the aid of PGP. Of course, ! 1036: you still need PGP to actually check the signature. ! 1037: ! 1038: To enable this feature, set CLEARSIG=ON, and set ARMOR=ON (or use ! 1039: the -a option), and set TEXTMODE=ON (or use the -t option). For ! 1040: example, you can set CLEARSIG directly from the command line: ! 1041: ! 1042: pgp -sta +clearsig=on message.txt ! 1043: ! 1044: This message representation is analogous to the MIC-CLEAR message type ! 1045: used in Internet Privacy Enhanced Mail (PEM). It is important to ! 1046: note that since this method only applies ASCII armor to the binary ! 1047: signature certificate, and not to the message text itself, there is ! 1048: some risk that the unarmored message may suffer some accidental ! 1049: molestation while en route. This can happen if it passes through ! 1050: some E-mail gateway that performs character set conversions, or in ! 1051: some cases extra spaces may be added to or stripped from the ends of ! 1052: lines. If this occurs, the signature will fail to verify, which may ! 1053: give a false indication of intentional tampering. But since PEM ! 1054: lives under a similar vulnerability, it seems worth having this ! 1055: feature despite the risks. ! 1056: ! 1057: Beginning with PGP version 2.2, trailing blanks are ignored on each ! 1058: line in calculating the signature for text in CLEARSIG mode. ! 1059: ! 1060: ! 1061: VERBOSE - Quiet, Normal, or Verbose Messages ! 1062: -------------------------------------------- ! 1063: ! 1064: Default setting: VERBOSE = 1 ! 1065: ! 1066: VERBOSE may be set to 0, 1, or 2, depending on how much detail you ! 1067: want to see from PGP diagnostic messages. The settings are: ! 1068: ! 1069: 0 - Display messages only if there is a problem. Unix fans wanted ! 1070: this "quiet mode" setting. ! 1071: ! 1072: 1 - Normal default setting. Displays a reasonable amount of detail ! 1073: in diagnostic or advisory messages. ! 1074: ! 1075: 2 - Displays maximum information, usually to help diagnose problems ! 1076: in PGP. Not recommended for normal use. Besides, PGP doesn't have ! 1077: any problems, right? ! 1078: ! 1079: ! 1080: INTERACTIVE - Ask for Confirmation for Key Adds ! 1081: ----------------------------------------------- ! 1082: ! 1083: Default Setting: INTERACTIVE = off ! 1084: ! 1085: Enabling this mode will mean that if you add a key file containing ! 1086: multiple keys to your key ring, PGP will ask for confirmation for ! 1087: each key before adding it to your key ring. ! 1088: ! 1089: ! 1090: ! 1091: Protecting Against Bogus Timestamps ! 1092: =================================== ! 1093: ! 1094: A somewhat obscure vulnerability of PGP involves dishonest users ! 1095: creating bogus timestamps on their own public key certificates and ! 1096: signatures. You can skip over this section if you are a casual user ! 1097: and aren't deeply into obscure public key protocols. ! 1098: ! 1099: There's nothing to stop a dishonest user from altering the date and ! 1100: time setting of his own system's clock, and generating his own public ! 1101: key certificates and signatures that appear to have been created at a ! 1102: different time. He can make it appear that he signed something ! 1103: earlier or later than he actually did, or that his public/secret key ! 1104: pair was created earlier or later. This may have some legal or ! 1105: financial benefit to him, for example by creating some kind of ! 1106: loophole that might allow him to repudiate a signature. ! 1107: ! 1108: A remedy for this could involve some trustworthy Certifying Authority ! 1109: or notary that would create notarized signatures with a trustworthy ! 1110: timestamp. This might not necessarily require a centralized ! 1111: authority. Perhaps any trusted introducer or disinterested party ! 1112: could serve this function, the same way real notary publics do now. ! 1113: A public key certificate could be signed by the notary, and the ! 1114: trusted timestamp in the notary's signature would have some legal ! 1115: significance. The notary could enter the signed certificate into a ! 1116: special certificate log controlled by the notary. Anyone can read ! 1117: this log. ! 1118: ! 1119: The notary could also sign other people's signatures, creating a ! 1120: signature certificate of a signature certificate. This would serve ! 1121: as a witness to the signature the same way real notaries do now with ! 1122: paper. Again, the notary could enter the detached signature ! 1123: certificate (without the actual whole document that was signed) into ! 1124: a log controlled by the notary. The notary's signature would have a ! 1125: trusted timestamp, which might have greater credibility than the ! 1126: timestamp in the original signature. A signature becomes "legal" if ! 1127: it is signed and logged by the notary. ! 1128: ! 1129: This problem of certifying signatures with notaries and trusted ! 1130: timestamps warrants further discussion. This can of worms will not ! 1131: be fully covered here now. There is a good treatment of this topic ! 1132: in Denning's 1983 article in IEEE Computer (see references). There ! 1133: is much more detail to be worked out in these various certifying ! 1134: schemes. This will develop further as PGP usage increases and other ! 1135: public key products develop their own certifying schemes. ! 1136: ! 1137: ! 1138: A Peek Under the Hood ! 1139: ===================== ! 1140: ! 1141: Let's take a look at a few internal features of PGP. ! 1142: ! 1143: ! 1144: Random Numbers ! 1145: -------------- ! 1146: ! 1147: PGP uses a cryptographically strong pseudorandom number generator for ! 1148: creating temporary conventional session keys. The seed file for this ! 1149: is called "randseed.bin". It too can be kept in whatever directory ! 1150: is indicated by the PGPPATH environmental variable. If this random ! 1151: seed file does not exist, it is automatically created and seeded with ! 1152: truly random numbers derived from timing your keystroke latencies. ! 1153: ! 1154: This generator reseeds the disk file each time it is used by mixing ! 1155: in new key material partially derived with the time of day and other ! 1156: truly random sources. It uses the conventional encryption algorithm ! 1157: as an engine for the random number generator. The seed file contains ! 1158: both random seed material and random key material to key the ! 1159: conventional encryption engine for the random generator. ! 1160: ! 1161: This random seed file should be at least slightly protected from ! 1162: disclosure, to reduce the risk of an attacker deriving your next or ! 1163: previous session keys. The attacker would have a very hard time ! 1164: getting anything useful from capturing this random seed file, because ! 1165: the file is cryptographically laundered before and after each use. ! 1166: Nonetheless, it seems prudent to at least try to keep it from falling ! 1167: into the wrong hands. ! 1168: ! 1169: If you feel uneasy about trusting any algorithmically derived random ! 1170: number source however strong, keep in mind that you already trust the ! 1171: strength of the same conventional cipher to protect your messages. ! 1172: If it's strong enough for that, then it should be strong enough to ! 1173: use as a source of random numbers for temporary session keys. Note ! 1174: that PGP still uses truly random numbers from physical sources ! 1175: (mainly keyboard timings) to generate long-term public/secret key ! 1176: pairs. ! 1177: ! 1178: ! 1179: ! 1180: PGP's Conventional Encryption Algorithm ! 1181: --------------------------------------- ! 1182: ! 1183: As described earlier, PGP "bootstraps" into a conventional single-key ! 1184: encryption algorithm by using a public key algorithm to encipher the ! 1185: conventional session key and then switching to fast conventional ! 1186: cryptography. So let's talk about this conventional encryption ! 1187: algorithm. It isn't the DES. ! 1188: ! 1189: The Federal Data Encryption Standard (DES) is a good algorithm for ! 1190: most commercial applications. However, the Government does not trust ! 1191: the DES to protect its own classified data. Perhaps this is because ! 1192: the DES key length is 56 bits, short enough for a brute force attack ! 1193: with a special purpose machine built from massive numbers of DES ! 1194: chips. Also, Biham and Shamir have had some success recently on ! 1195: attacking the full 16-round DES. ! 1196: ! 1197: PGP does not use the DES as its conventional single-key algorithm to ! 1198: encrypt messages. Instead, PGP uses a different conventional ! 1199: single-key block encryption algorithm, called IDEA(tm). A future ! 1200: version of PGP may support the DES as an option, if enough users ! 1201: ask for it. But I suspect IDEA is better than DES. ! 1202: ! 1203: For the cryptographically curious, the IDEA cipher has a 64-bit block ! 1204: size for the plaintext and the ciphertext. It uses a key size of 128 ! 1205: bits. It is based on the design concept of "mixing operations from ! 1206: different algebraic groups". It runs much faster in software than ! 1207: the DES. Like the DES, it can be used in cipher feedback (CFB) and ! 1208: cipher block chaining (CBC) modes. PGP uses it in 64-bit CFB mode. ! 1209: ! 1210: The IPES/IDEA block cipher was developed at ETH in Zurich by James L. ! 1211: Massey and Xuejia Lai, and published in 1990. This is not a ! 1212: "home-grown" algorithm. Its designers have a distinguished ! 1213: reputation in the cryptologic community. Early published papers on ! 1214: the algorithm called it IPES (Improved Proposed Encryption Standard), ! 1215: but they later changed the name to IDEA (International Data ! 1216: Encryption Algorithm). So far, IDEA has resisted attack much better ! 1217: than other ciphers such as FEAL, REDOC-II, LOKI, Snefru and Khafre. ! 1218: And preliminary evidence suggests that IDEA may be more resistant ! 1219: than the DES to Biham & Shamir's highly successful differential ! 1220: cryptanalysis attack. Biham and Shamir have been examining the IDEA ! 1221: cipher for weaknesses, without success. Academic cryptanalyst groups ! 1222: in Belgium, England, and Germany are also attempting to attack it, as ! 1223: well as the military services from several European countries. As ! 1224: this new cipher continues to attract attack efforts from the most ! 1225: formidable quarters of the cryptanalytic world, confidence in IDEA is ! 1226: growing with the passage of time. ! 1227: ! 1228: A famous hockey player once said, "I try to skate to where I think ! 1229: the puck will be." A lot of people are starting to feel that the ! 1230: days are numbered for the DES. I'm skating toward IDEA. ! 1231: ! 1232: It is not ergonomically practical to use pure RSA with large keys to ! 1233: encrypt and decrypt long messages. Absolutely no one does it that way ! 1234: in the real world. But perhaps you are concerned that the whole ! 1235: package is weakened if we use a hybrid public-key and conventional ! 1236: scheme just to speed things up. After all, a chain is only as strong ! 1237: as its weakest link. Many people less experienced in cryptography ! 1238: mistakenly believe that RSA is intrinsically stronger than any ! 1239: conventional cipher. It's not. RSA can be made weak by using weak ! 1240: keys, and conventional ciphers can be made strong by choosing good ! 1241: algorithms. It's usually difficult to tell exactly how strong a good ! 1242: conventional cipher is, without actually cracking it. A really good ! 1243: conventional cipher might possibly be harder to crack than even a ! 1244: "military grade" RSA key. The attraction of public key cryptography ! 1245: is not because it is intrinsically stronger than a conventional ! 1246: cipher-- its appeal is because it helps you manage keys more ! 1247: conveniently. ! 1248: ! 1249: ! 1250: ! 1251: Data Compression ! 1252: ---------------- ! 1253: ! 1254: PGP normally compresses the plaintext before encrypting it. It's too ! 1255: late to compress it after it has been encrypted; encrypted data is ! 1256: incompressible. Data compression saves modem transmission time and ! 1257: disk space and more importantly strengthens cryptographic security. ! 1258: Most cryptanalysis techniques exploit redundancies found in the ! 1259: plaintext to crack the cipher. Data compression reduces this ! 1260: redundancy in the plaintext, thereby greatly enhancing resistance to ! 1261: cryptanalysis. It takes extra time to compress the plaintext, but ! 1262: from a security point of view it seems worth it, at least in my ! 1263: cautious opinion. ! 1264: ! 1265: Files that are too short to compress or just don't compress well are ! 1266: not compressed by PGP. ! 1267: ! 1268: If you prefer, you can use PKZIP to compress the plaintext before ! 1269: encrypting it. PKZIP is a widely-available and effective MSDOS ! 1270: shareware compression utility from PKWare, Inc. Or you can use ZIP, ! 1271: a PKZIP-compatible freeware compression utility on Unix and other ! 1272: systems, available from Jean-Loup Gailly. There is some advantage in ! 1273: using PKZIP or ZIP in certain cases, because unlike PGP's built-in ! 1274: compression algorithm, PKZIP and ZIP have the nice feature of ! 1275: compressing multiple files into a single compressed file, which is ! 1276: reconstituted again into separate files when decompressed. PGP will ! 1277: not try to compress a plaintext file that has already been ! 1278: compressed. After decrypting, the recipient can decompress the ! 1279: plaintext with PKUNZIP. If the decrypted plaintext is a PKZIP ! 1280: compressed file, PGP automatically recognizes this and advises the ! 1281: recipient that the decrypted plaintext appears to be a PKZIP file. ! 1282: ! 1283: For the technically curious readers, the current version of PGP uses ! 1284: the freeware ZIP compression routines written by Jean-loup Gailly, ! 1285: Mark Adler, and Richard B. Wales. This ZIP software uses ! 1286: functionally-equivalent compression algorithms as those used by ! 1287: PKWare's new PKZIP 2.0. This ZIP compression software was selected ! 1288: for PGP mainly because of its free portable C source code ! 1289: availability, and because it has a really good compression ratio, and ! 1290: because it's fast. ! 1291: ! 1292: Peter Gutmann has also written a nice compression utility called ! 1293: HPACK, available for free from many Internet FTP sites. It encrypts ! 1294: the compressed archives, using PGP data formats and key rings. He ! 1295: wanted me to mention that here. ! 1296: ! 1297: ! 1298: ! 1299: Message Digests and Digital Signatures ! 1300: -------------------------------------- ! 1301: ! 1302: To create a digital signature, PGP encrypts with your secret key. ! 1303: But PGP doesn't actually encrypt your entire message with your secret ! 1304: key-- that would take too long. Instead, PGP encrypts a "message ! 1305: digest". ! 1306: ! 1307: The message digest is a compact (128 bit) "distillate" of your ! 1308: message, similar in concept to a checksum. You can also think of it ! 1309: as a "fingerprint" of the message. The message digest "represents" ! 1310: your message, such that if the message were altered in any way, a ! 1311: different message digest would be computed from it. This makes it ! 1312: possible to detect any changes made to the message by a forger. A ! 1313: message digest is computed using a cryptographically strong one-way ! 1314: hash function of the message. It would be computationally infeasible ! 1315: for an attacker to devise a substitute message that would produce an ! 1316: identical message digest. In that respect, a message digest is much ! 1317: better than a checksum, because it is easy to devise a different ! 1318: message that would produce the same checksum. But like a checksum, ! 1319: you can't derive the original message from its message digest. ! 1320: ! 1321: A message digest alone is not enough to authenticate a message. The ! 1322: message digest algorithm is publicly known, and does not require ! 1323: knowledge of any secret keys to calculate. If all we did was attach ! 1324: a message digest to a message, then a forger could alter a message ! 1325: and simply attach a new message digest calculated from the new ! 1326: altered message. To provide real authentication, the sender has to ! 1327: encrypt (sign) the message digest with his secret key. ! 1328: ! 1329: A message digest is calculated from the message by the sender. The ! 1330: sender's secret key is used to encrypt the message digest and an ! 1331: electronic timestamp, forming a digital signature, or signature ! 1332: certificate. The sender sends the digital signature along with the ! 1333: message. The receiver receives the message and the digital ! 1334: signature, and recovers the original message digest from the digital ! 1335: signature by decrypting it with the sender's public key. The ! 1336: receiver computes a new message digest from the message, and checks ! 1337: to see if it matches the one recovered from the digital signature. If ! 1338: it matches, then that proves the message was not altered, and it came ! 1339: from the sender who owns the public key used to check the signature. ! 1340: ! 1341: A potential forger would have to either produce an altered message ! 1342: that produces an identical message digest (which is infeasible), or ! 1343: he would have to create a new digital signature from a different ! 1344: message digest (also infeasible, without knowing the true sender's ! 1345: secret key). ! 1346: ! 1347: Digital signatures prove who sent the message, and that the message ! 1348: was not altered either by error or design. It also provides ! 1349: non-repudiation, which means the sender cannot easily disavow his ! 1350: signature on the message. ! 1351: ! 1352: Using message digests to form digital signatures has other advantages ! 1353: besides being faster than directly signing the entire actual message ! 1354: with the secret key. Using message digests allows signatures to be ! 1355: of a standard small fixed size, regardless of the size of the actual ! 1356: message. It also allows the software to check the message integrity ! 1357: automatically, in a manner similar to using checksums. And it allows ! 1358: signatures to be stored separately from messages, perhaps even in a ! 1359: public archive, without revealing sensitive information about the ! 1360: actual messages, because no one can derive any message content from a ! 1361: message digest. ! 1362: ! 1363: The message digest algorithm used here is the MD5 Message Digest ! 1364: Algorithm, placed in the public domain by RSA Data Security, Inc. ! 1365: MD5's designer, Ronald Rivest, writes this about MD5: ! 1366: ! 1367: "It is conjectured that the difficulty of coming up with two messages ! 1368: having the same message digest is on the order of 2^64 operations, ! 1369: and that the difficulty of coming up with any message having a given ! 1370: message digest is on the order of 2^128 operations. The MD5 ! 1371: algorithm has been carefully scrutinized for weaknesses. It is, ! 1372: however, a relatively new algorithm and further security analysis is ! 1373: of course justified, as is the case with any new proposal of this ! 1374: sort. The level of security provided by MD5 should be sufficient for ! 1375: implementing very high security hybrid digital signature schemes ! 1376: based on MD5 and the RSA public-key cryptosystem." ! 1377: ! 1378: ! 1379: ! 1380: Compatibility with Previous Versions of PGP ! 1381: =========================================== ! 1382: ! 1383: I'm sorry, PGP version 2.0 is not compatible with PGP version 1.0. ! 1384: If you have keys generated with version 1.0, you will have to ! 1385: generate new keys to use with this version. This version of PGP uses ! 1386: all new algorithms for conventional cryptography, compression, and ! 1387: message digests, as well as using a much better approach to key ! 1388: management. There were just too many changes to make it compatible ! 1389: with the old format messages, signatures, and keys. Perhaps we could ! 1390: have provided a special conversion utility to convert old keys into ! 1391: new keys, but we were all tired and wanted to get the new release out ! 1392: the door. Besides, converting the old keys into new keys would ! 1393: probably create more problems than it would solve, because we have ! 1394: changed to a new recommended uniform style for the user ID that ! 1395: includes the full name and E-mail address in a particular syntax. ! 1396: ! 1397: There is compatibility from version 2.0 to higher versions. Because ! 1398: new features are added, older versions may not always be able to ! 1399: handle some files created with newer versions. ! 1400: ! 1401: We made some effort to design the internal data structures of this ! 1402: version of PGP to be adaptable to future changes, so that hopefully ! 1403: you will not be required to discard and regenerate your keys in future ! 1404: versions. ! 1405: ! 1406: ! 1407: Vulnerabilities ! 1408: =============== ! 1409: ! 1410: No data security system is impenetrable. PGP can be circumvented in ! 1411: a variety of ways. In any data security system, you have to ask ! 1412: yourself if the information you are trying to protect is more ! 1413: valuable to your attacker than the cost of the attack. This should ! 1414: lead you to protecting yourself from the cheapest attacks, while not ! 1415: worrying about the more expensive attacks. ! 1416: ! 1417: Some of the discussion that follows may seem unduly paranoid, but ! 1418: such an attitude is appropriate for a reasonable discussion of ! 1419: vulnerability issues. ! 1420: ! 1421: ! 1422: Compromised Pass Phrase and Secret Key ! 1423: -------------------------------------- ! 1424: ! 1425: Probably the simplest attack is if you leave your pass phrase for ! 1426: your secret key written down somewhere. If someone gets it and also ! 1427: gets your secret key file, they can read your messages and make ! 1428: signatures in your name. ! 1429: ! 1430: Don't use obvious passwords that can be easily guessed, such as the ! 1431: names of your kids or spouse. If you make your pass phrase a single ! 1432: word, it can be easily guessed by having a computer try all the words ! 1433: in the dictionary until it finds your password. That's why a pass ! 1434: phrase is so much better than a password. A more sophisticated ! 1435: attacker may have his computer scan a book of famous quotations to ! 1436: find your pass phrase. An easy to remember but hard to guess pass ! 1437: phrase can be easily constructed by some creatively nonsensical ! 1438: sayings or very obscure literary quotes. ! 1439: ! 1440: For further details, see the section "How to Protect Secret Keys from ! 1441: Disclosure" in the Essential Topics volume of the PGP User's Guide. ! 1442: ! 1443: ! 1444: Public Key Tampering ! 1445: -------------------- ! 1446: ! 1447: A major vulnerability exists if public keys are tampered with. This ! 1448: may be the most crucially important vulnerability of a public key ! 1449: cryptosystem, in part because most novices don't immediately ! 1450: recognize it. The importance of this vulnerability, and appropriate ! 1451: hygienic countermeasures, are detailed in the section "How to Protect ! 1452: Public Keys from Tampering" in the Essential Topics volume. ! 1453: ! 1454: To summarize: When you use someone's public key, make certain it has ! 1455: not been tampered with. A new public key from someone else should be ! 1456: trusted only if you got it directly from its owner, or if it has been ! 1457: signed by someone you trust. Make sure no one else can tamper with ! 1458: your own public key ring. Maintain physical control of both your ! 1459: public key ring and your secret key ring, preferably on your own ! 1460: personal computer rather than on a remote timesharing system. Keep a ! 1461: backup copy of both key rings. ! 1462: ! 1463: ! 1464: "Not Quite Deleted" Files ! 1465: ------------------------- ! 1466: ! 1467: Another potential security problem is caused by how most operating ! 1468: systems delete files. When you encrypt a file and then delete the ! 1469: original plaintext file, the operating system doesn't actually ! 1470: physically erase the data. It merely marks those disk blocks as ! 1471: deleted, allowing the space to be reused later. It's sort of like ! 1472: discarding sensitive paper documents in the paper recycling bin ! 1473: instead of the paper shredder. The disk blocks still contain the ! 1474: original sensitive data you wanted to erase, and will probably ! 1475: eventually be overwritten by new data at some point in the future. ! 1476: If an attacker reads these deleted disk blocks soon after they have ! 1477: been deallocated, he could recover your plaintext. ! 1478: ! 1479: In fact this could even happen accidentally, if for some reason ! 1480: something went wrong with the disk and some files were accidentally ! 1481: deleted or corrupted. A disk recovery program may be run to recover ! 1482: the damaged files, but this often means some previously deleted files ! 1483: are resurrected along with everything else. Your confidential files ! 1484: that you thought were gone forever could then reappear and be ! 1485: inspected by whomever is attempting to recover your damaged disk. ! 1486: Even while you are creating the original message with a word ! 1487: processor or text editor, the editor may be creating multiple ! 1488: temporary copies of your text on the disk, just because of its ! 1489: internal workings. These temporary copies of your text are deleted ! 1490: by the word processor when it's done, but these sensitive fragments ! 1491: are still on your disk somewhere. ! 1492: ! 1493: Let me tell you a true horror story. I had a friend, married with ! 1494: young children, who once had a brief and not very serious affair. ! 1495: She wrote a letter to her lover on her word processor, and deleted ! 1496: the letter after she sent it. Later, after the affair was over, the ! 1497: floppy disk got damaged somehow and she had to recover it because it ! 1498: contained other important documents. She asked her husband to ! 1499: salvage the disk, which seemed perfectly safe because she knew she ! 1500: had deleted the incriminating letter. Her husband ran a commercial ! 1501: disk recovery software package to salvage the files. It recovered ! 1502: the files alright, including the deleted letter. He read it, which ! 1503: set off a tragic chain of events. ! 1504: ! 1505: The only way to prevent the plaintext from reappearing is to somehow ! 1506: cause the deleted plaintext files to be overwritten. Unless you know ! 1507: for sure that all the deleted disk blocks will soon be reused, you ! 1508: must take positive steps to overwrite the plaintext file, and also ! 1509: any fragments of it on the disk left by your word processor. You can ! 1510: overwrite the original plaintext file after encryption by using the ! 1511: PGP -w (wipe) option. You can take care of any fragments of the ! 1512: plaintext left on the disk by using any of the disk utilities ! 1513: available that can overwrite all of the unused blocks on a disk. For ! 1514: example, the Norton Utilities for MSDOS can do this. ! 1515: ! 1516: Even if you overwrite the plaintext data on the disk, it may still be ! 1517: possible for a resourceful and determined attacker to recover the ! 1518: data. Faint magnetic traces of the original data remain on the disk ! 1519: after it has been overwritten. Special sophisticated disk recovery ! 1520: hardware can sometimes be used to recover the data. ! 1521: ! 1522: ! 1523: Viruses and Trojan Horses ! 1524: ------------------------- ! 1525: ! 1526: Another attack could involve a specially-tailored hostile computer ! 1527: virus or worm that might infect PGP or your operating system. This ! 1528: hypothetical virus could be designed to capture your pass phrase or ! 1529: secret key or deciphered messages, and covertly write the captured ! 1530: information to a file or send it through a network to the virus's ! 1531: owner. Or it might alter PGP's behavior so that signatures are not ! 1532: properly checked. This attack is cheaper than cryptanalytic attacks. ! 1533: ! 1534: Defending against this falls under the category of defending against ! 1535: viral infection generally. There are some moderately capable ! 1536: anti-viral products commercially available, and there are hygienic ! 1537: procedures to follow that can greatly reduce the chances of viral ! 1538: infection. A complete treatment of anti-viral and anti-worm ! 1539: countermeasures is beyond the scope of this document. PGP has no ! 1540: defenses against viruses, and assumes your own personal computer is a ! 1541: trustworthy execution environment. If such a virus or worm actually ! 1542: appeared, hopefully word would soon get around warning everyone. ! 1543: ! 1544: Another similar attack involves someone creating a clever imitation ! 1545: of PGP that behaves like PGP in most respects, but doesn't work the ! 1546: way it's supposed to. For example, it might be deliberately crippled ! 1547: to not check signatures properly, allowing bogus key certificates to ! 1548: be accepted. This "Trojan horse" version of PGP is not hard for an ! 1549: attacker to create, because PGP source code is widely available, so ! 1550: anyone could modify the source code and produce a lobotomized zombie ! 1551: imitation PGP that looks real but does the bidding of its diabolical ! 1552: master. This Trojan horse version of PGP could then be widely ! 1553: circulated, claiming to be from me. How insidious. ! 1554: ! 1555: You should make an effort to get your copy of PGP from a reliable ! 1556: source, whatever that means. Or perhaps from more than one ! 1557: independent source, and compare them with a file comparison utility. ! 1558: ! 1559: There are other ways to check PGP for tampering, using digital ! 1560: signatures. If someone you trust signs the executable version of ! 1561: PGP, vouching for the fact that it has not been infected or tampered ! 1562: with, you can be reasonably sure that you have a good copy. You ! 1563: could use an earlier trusted version of PGP to check the signature on ! 1564: a later suspect version of PGP. But this will not help at all if ! 1565: your operating system is infected, nor will it detect if your ! 1566: original copy of PGP.EXE has been maliciously altered in such a way ! 1567: as to compromise its own ability to check signatures. This test also ! 1568: assumes that you have a good trusted copy of the public key that you ! 1569: use to check the signature on the PGP executable. ! 1570: ! 1571: ! 1572: Physical Security Breach ! 1573: ------------------------ ! 1574: ! 1575: A physical security breach may allow someone to physically acquire ! 1576: your plaintext files or printed messages. A determined opponent ! 1577: might accomplish this through burglary, trash-picking, unreasonable ! 1578: search and seizure, or bribery, blackmail or infiltration of your ! 1579: staff. Some of these attacks may be especially feasible against ! 1580: grassroots political organizations that depend on a largely volunteer ! 1581: staff. It has been widely reported in the press that the FBI's ! 1582: COINTELPRO program used burglary, infiltration, and illegal bugging ! 1583: against antiwar and civil rights groups. And look what happened at ! 1584: the Watergate Hotel. ! 1585: ! 1586: Don't be lulled into a false sense of security just because you have ! 1587: a cryptographic tool. Cryptographic techniques protect data only ! 1588: while it's encrypted-- direct physical security violations can still ! 1589: compromise plaintext data or written or spoken information. ! 1590: ! 1591: This kind of attack is cheaper than cryptanalytic attacks on PGP. ! 1592: ! 1593: ! 1594: Tempest Attacks ! 1595: --------------- ! 1596: ! 1597: Another kind of attack that has been used by well-equipped opponents ! 1598: involves the remote detection of the electromagnetic signals from ! 1599: your computer. This expensive and somewhat labor-intensive attack is ! 1600: probably still cheaper than direct cryptanalytic attacks. An ! 1601: appropriately instrumented van can park near your office and remotely ! 1602: pick up all of your keystrokes and messages displayed on your ! 1603: computer video screen. This would compromise all of your passwords, ! 1604: messages, etc. This attack can be thwarted by properly shielding all ! 1605: of your computer equipment and network cabling so that it does not ! 1606: emit these signals. This shielding technology is known as "Tempest", ! 1607: and is used by some Government agencies and defense contractors. ! 1608: There are hardware vendors who supply Tempest shielding commercially, ! 1609: although it may be subject to some kind of Government licensing. Now ! 1610: why do you suppose the Government would restrict access to Tempest ! 1611: shielding? ! 1612: ! 1613: ! 1614: Exposure on Multi-user Systems ! 1615: ------------------------------ ! 1616: ! 1617: PGP was originally designed for a single-user MSDOS machine under ! 1618: your direct physical control. I run PGP at home on my own PC, and ! 1619: unless someone breaks into my house or monitors my electromagnetic ! 1620: emissions, they probably can't see my plaintext files or secret keys. ! 1621: ! 1622: But now PGP also runs on multi-user systems such as Unix and VAX/VMS. ! 1623: On multi-user systems, there are much greater risks of your plaintext ! 1624: or keys or passwords being exposed. The Unix system administrator or ! 1625: a clever intruder can read your plaintext files, or perhaps even use ! 1626: special software to covertly monitor your keystrokes or read what's ! 1627: on your screen. On a Unix system, any other user can read your ! 1628: environment information remotely by simply using the Unix "ps" ! 1629: command. Similar problems exist for MSDOS machines connected on a ! 1630: local area network. The actual security risk is dependent on your ! 1631: particular situation. Some multi-user systems may be safe because ! 1632: all the users are trusted, or because they have system security ! 1633: measures that are safe enough to withstand the attacks available to ! 1634: the intruders, or because there just aren't any sufficiently ! 1635: interested intruders. Some Unix systems are safe because they are ! 1636: only used by one user-- there are even some notebook computers ! 1637: running Unix. It would be unreasonable to simply exclude PGP from ! 1638: running on all Unix systems. ! 1639: ! 1640: PGP is not designed to protect your data while it is in plaintext ! 1641: form on a compromised system. Nor can it prevent an intruder from ! 1642: using sophisticated measures to read your secret key while it is ! 1643: being used. You will just have to recognize these risks on ! 1644: multi-user systems, and adjust your expectations and behavior ! 1645: accordingly. Perhaps your situation is such that you should consider ! 1646: only running PGP on an isolated single-user system under your direct ! 1647: physical control. That's what I do, and that's what I recommend. ! 1648: ! 1649: ! 1650: Traffic Analysis ! 1651: ---------------- ! 1652: ! 1653: Even if the attacker cannot read the contents of your encrypted ! 1654: messages, he may be able to infer at least some useful information by ! 1655: observing where the messages come from and where they are going, the ! 1656: size of the messages, and the time of day the messages are sent. ! 1657: This is analogous to the attacker looking at your long distance phone ! 1658: bill to see who you called and when and for how long, even though the ! 1659: actual content of your calls is unknown to the attacker. This is ! 1660: called traffic analysis. PGP alone does not protect against traffic ! 1661: analysis. Solving this problem would require specialized ! 1662: communication protocols designed to reduce exposure to traffic ! 1663: analysis in your communication environment, possibly with some ! 1664: cryptographic assistance. ! 1665: ! 1666: ! 1667: Cryptanalysis ! 1668: ------------- ! 1669: ! 1670: An expensive and formidable cryptanalytic attack could possibly be ! 1671: mounted by someone with vast supercomputer resources, such as a ! 1672: Government intelligence agency. They might crack your RSA key by ! 1673: using some new secret factoring breakthrough. Perhaps so, but it is ! 1674: noteworthy that the US Government trusts the RSA algorithm enough in ! 1675: some cases to use it to protect its own nuclear weapons, according to ! 1676: Ron Rivest. And civilian academia has been intensively attacking it ! 1677: without success since 1978. ! 1678: ! 1679: Perhaps the Government has some classified methods of cracking the ! 1680: IDEA(tm) conventional encryption algorithm used in PGP. This is ! 1681: every cryptographer's worst nightmare. There can be no absolute ! 1682: security guarantees in practical cryptographic implementations. ! 1683: ! 1684: Still, some optimism seems justified. The IDEA algorithm's designers ! 1685: are among the best cryptographers in Europe. It has had extensive ! 1686: security analysis and peer review from some of the best cryptanalysts ! 1687: in the unclassified world. It appears to have some design advantages ! 1688: over the DES in withstanding differential cryptanalysis, which has ! 1689: been used to crack the DES. ! 1690: ! 1691: Besides, even if this algorithm has some subtle unknown weaknesses, ! 1692: PGP compresses the plaintext before encryption, which should greatly ! 1693: reduce those weaknesses. The computational workload to crack it is ! 1694: likely to be much more expensive than the value of the message. ! 1695: ! 1696: If your situation justifies worrying about very formidable attacks of ! 1697: this caliber, then perhaps you should contact a data security ! 1698: consultant for some customized data security approaches tailored to ! 1699: your special needs. Boulder Software Engineering, whose address and ! 1700: phone are given at the end of this document, can provide such ! 1701: services. ! 1702: ! 1703: ! 1704: In summary, without good cryptographic protection of your data ! 1705: communications, it may have been practically effortless and perhaps ! 1706: even routine for an opponent to intercept your messages, especially ! 1707: those sent through a modem or E-mail system. If you use PGP and ! 1708: follow reasonable precautions, the attacker will have to expend far ! 1709: more effort and expense to violate your privacy. ! 1710: ! 1711: If you protect yourself against the simplest attacks, and you feel ! 1712: confident that your privacy is not going to be violated by a ! 1713: determined and highly resourceful attacker, then you'll probably be ! 1714: safe using PGP. PGP gives you Pretty Good Privacy. ! 1715: ! 1716: ! 1717: Legal Issues ! 1718: ============ ! 1719: ! 1720: ! 1721: Trademarks, Copyrights, and Warranties ! 1722: -------------------------------------- ! 1723: ! 1724: "Pretty Good Privacy", "Phil's Pretty Good Software", and the "Pretty ! 1725: Good" label for computer software and hardware products are all ! 1726: trademarks of Philip Zimmermann and Phil's Pretty Good Software. PGP ! 1727: is (c) Copyright Philip R. Zimmermann, 1990-1993. Philip Zimmermann ! 1728: also holds the copyright for the PGP User's Manual, as well as any ! 1729: foreign language translations of the manual or the software. ! 1730: ! 1731: The author assumes no liability for damages resulting from the use of ! 1732: this software, even if the damage results from defects in this ! 1733: software, and makes no representations concerning the merchantability ! 1734: of this software or its suitability for any specific purpose. It is ! 1735: provided "as is" without express or implied warranty of any kind. ! 1736: ! 1737: ! 1738: Patent Rights on the Algorithms ! 1739: ------------------------------- ! 1740: ! 1741: When I first released PGP, I half-expected to encounter some form of ! 1742: legal harassment from the Government. Indeed, there has been legal ! 1743: harrassment, but it hasn't come from the Government-- it has come ! 1744: from a private corporation. ! 1745: ! 1746: The RSA public key cryptosystem was developed at MIT with Federal ! 1747: funding from grants from the National Science Foundation and the ! 1748: Navy. It is patented by MIT (U.S. patent #4,405,829, issued 20 Sep ! 1749: 1983). A company in California called Public Key Partners (PKP) holds ! 1750: the exclusive commercial license to sell and sub-license the RSA ! 1751: public key cryptosystem. The author of this software implementation ! 1752: of the RSA algorithm is providing this implementation for educational ! 1753: use only. Licensing this algorithm from PKP is the responsibility of ! 1754: you, the user, not Philip Zimmermann, the author of this software ! 1755: implementation. The author assumes no liability for any patent ! 1756: infringement that may result from the unlicensed use by the user of ! 1757: the underlying RSA algorithm used in this software. Foreign users ! 1758: should note that the RSA patent does not apply outside the US, and ! 1759: there is no RSA patent in any other country. Federal agencies may ! 1760: use it because the Government paid for the development of RSA. ! 1761: ! 1762: Unfortunately, PKP is not offering any licensing of their RSA patent ! 1763: to end users of PGP. This essentially makes PGP contraband in the ! 1764: USA. Jim Bidzos, president of PKP, threatened to take legal action ! 1765: against me unless I stop distributing PGP, until they can devise a ! 1766: licensing scheme for it. I agreed to this, since PGP is already in ! 1767: wide circulation and waiting a while for a licensing arrangement from ! 1768: PKP seemed reasonable. Mr. Bidzos assured me (he even used the word ! 1769: "promise") several times since the initial 5 June 91 release of PGP ! 1770: that they were working on a licensing scheme for PGP. Apparently, my ! 1771: release of PGP helped provide the impetus for them to offer some sort ! 1772: of a freeware-style license for noncommercial use of the RSA ! 1773: algorithm. However, in December 1991 Mr. Bidzos said he had no plans ! 1774: to ever license the RSA algorithm to PGP users, and denied ever ! 1775: implying that he would. Meanwhile, I have continued to refrain from ! 1776: distributing PGP, although I continue to update the PGP User's Guide, ! 1777: and have provided the design guidance for new revisions of PGP. ! 1778: Ironically, all this legal controversy from PKP has imparted a ! 1779: forbidden flavor to PGP that has only served to amplify its universal ! 1780: popularity. ! 1781: ! 1782: I wrote my PGP software from scratch, with my own implementation of ! 1783: the RSA algorithm. I didn't steal any software from PKP. Before ! 1784: publishing PGP, I got a formal written legal opinion from a patent ! 1785: attorney with extensive experience in software patents. I'm ! 1786: convinced that publishing PGP the way I did does not violate patent ! 1787: law. However, it is a well known axiom in the US legal system that ! 1788: regardless of the law, he with the most money and lawyers prevails, ! 1789: if not by actually winning then by crushing the little guy with legal ! 1790: expenses. ! 1791: ! 1792: Not only did PKP acquire the exclusive patent rights for the RSA ! 1793: cryptosystem, which was developed with your tax dollars, but they ! 1794: also somehow acquired the exclusive rights to three other patents ! 1795: covering rival public key schemes invented by others, also developed ! 1796: with your tax dollars. This essentially gives one company a legal ! 1797: lock in the USA on nearly all practical public key cryptosystems. ! 1798: They even appear to be claiming patent rights on the very concept of ! 1799: public key cryptography, regardless of what clever new original ! 1800: algorithms are independently invented by others. And you thought ! 1801: patent law was designed to encourage innovation! PKP does not ! 1802: actually develop any software-- they don't even have an engineering ! 1803: department-- they are essentially a litigation company. ! 1804: ! 1805: Public key cryptography is destined to become a crucial technology in ! 1806: the protection of our civil liberties and privacy in our increasingly ! 1807: connected society. Why should the Government try to limit access to ! 1808: this key technology, when a single monopoly can do it for them? ! 1809: ! 1810: It appears certain that there will be future releases of PGP, ! 1811: regardless of the outcome of licensing problems with Public Key ! 1812: Partners. If PKP does not license PGP, then future releases of PGP ! 1813: might not come from me. There are countless fans of PGP outside the ! 1814: US, and many of them are software engineers who want to improve PGP ! 1815: and promote it, regardless of what I do. The second release of PGP ! 1816: was a joint effort of an international team of software engineers, ! 1817: implementing enhancements to the original PGP with design guidance ! 1818: from me. It was released by Branko Lankester in The Netherlands and ! 1819: Peter Gutmann in New Zealand, out of reach of US patent law. ! 1820: Although released only in Europe and New Zealand, it spontaneously ! 1821: spread to the USA without help from me or the PGP development team. ! 1822: ! 1823: The IDEA(tm) conventional block cipher used by PGP is covered by a ! 1824: patent in Europe, held by ETH and a Swiss company called Ascom-Tech ! 1825: AG. The patent number is PCT/CH91/00117. International patents are ! 1826: pending. IDEA(tm) is a trademark of Ascom-Tech AG. There is no ! 1827: license fee required for noncommercial use of IDEA. Ascom Tech AG ! 1828: has granted permission for PGP to use the IDEA cipher, and places no ! 1829: restrictions on using PGP for any purpose, including commercial use. ! 1830: You may not extract the IDEA cipher from PGP and put it in another ! 1831: commercial product without a license. Commercial users of IDEA may ! 1832: obtain licensing details from Dieter Profos, Ascom Tech AG, Solothurn ! 1833: Lab, Postfach 151, 4502 Solothurn, Switzerland, Tel +41 65 242885, ! 1834: Fax +41 65 235761. ! 1835: ! 1836: The ZIP compression routines in PGP come from freeware source code, ! 1837: with the author's permission. I'm not aware of any patents on the ! 1838: ZIP algorithm, but you're welcome to check into that question ! 1839: yourself. If there are any obscure patent claims that apply to ZIP, ! 1840: then sorry, you'll have to take care of the patent licensing, not me. ! 1841: ! 1842: All this patent stuff reminds me of a Peanuts cartoon I saw in the ! 1843: newspaper where Lucy showed Charlie Brown a fallen autumn leaf and ! 1844: said "This is the first leaf to fall this year." Charlie Brown said, ! 1845: "How do you know that? Leaves have been falling for weeks." Lucy ! 1846: replied, "I had this one notarized." ! 1847: ! 1848: ! 1849: Licensing and Distribution ! 1850: -------------------------- ! 1851: ! 1852: In the USA PKP controls, through US patent law, the licensing of the ! 1853: RSA algorithm. But I have no objection to anyone freely using or ! 1854: distributing my PGP software, without payment of fees to me. You must ! 1855: keep the copyright notices on PGP and keep this documentation with ! 1856: it. However, if you live in the USA, this may not satisfy any legal ! 1857: obligations you may have to PKP for using the RSA algorithm as ! 1858: mentioned above. ! 1859: ! 1860: In fact, if you live in the USA, and you are not a Federal agency, ! 1861: you shouldn't actually run PGP on your computer, because Public Key ! 1862: Partners wants to forbid you from running my software. PGP is ! 1863: contraband. ! 1864: ! 1865: Of course, I can't give any assurances, but my guess is that it seems ! 1866: unlikely that PKP would waste their time pursuing PGP end users for ! 1867: patent infringement. There are just too many PGP users to go after. ! 1868: And why would they single you out? But I certainly wouldn't want to ! 1869: imply that you do anything improper-- if PKP were offering licenses, ! 1870: I would urge you to obtain one. But since they aren't, well, I guess ! 1871: you should just refrain from using PGP if you live in the USA. ! 1872: ! 1873: PGP is not shareware, it's freeware. Forbidden freeware. Published ! 1874: as a community service. If I sold PGP for money, then I would get ! 1875: sued by PKP for using their RSA algorithm. More importantly, giving ! 1876: PGP away for free will encourage far more people to use it, which ! 1877: hopefully will have a greater social impact. This could lead to ! 1878: widespread awareness and use of the RSA public key cryptosystem, ! 1879: which will probably make more money for PKP in the long run. If only ! 1880: they could see that. ! 1881: ! 1882: All the source code for PGP is available for free under the "Copyleft" ! 1883: General Public License from the Free Software Foundation (FSF). A ! 1884: copy of the FSF General Public License is included in the source ! 1885: release package of PGP. ! 1886: ! 1887: Regardless of and perhaps contrary to some provisions of the FSF ! 1888: General Public License, the following terms apply: ! 1889: ! 1890: 1) Written discussions of PGP in magazines or books may include ! 1891: fragments of PGP source code and documentation, without ! 1892: restrictions. ! 1893: ! 1894: 2) Although the FSF General Public License allows non-proprietary ! 1895: derivative products, it prohibits proprietary derivative products. ! 1896: Despite this, I may grant you a special license if you want to ! 1897: derive a proprietary commercial product from some of PGP's parts. ! 1898: There may or may not be a fee depending on what kind of a deal you ! 1899: plan to pursue with PKP. Retaining my copyright notice and ! 1900: attribution might suffice in some cases. Give me a call and we'll ! 1901: discuss it. I'm real easy to please. ! 1902: ! 1903: Feel free to disseminate the complete PGP release package as widely ! 1904: as possible. Give it to all your friends. If you have access to any ! 1905: electronic Bulletin Boards Systems, please upload the complete PGP ! 1906: executable object release package to as many BBS's as possible. You ! 1907: may disseminate the PGP source release package too, if you've got ! 1908: it. The PGP version 2.2 executable object release package for MSDOS ! 1909: contains the PGP executable software, documentation, sample key rings ! 1910: including my own public key, and signatures for the software and this ! 1911: manual, all in one PKZIP compressed file called PGP22.ZIP. The PGP ! 1912: source release package for MSDOS contains all the C source files in ! 1913: one PKZIP compressed file called PGP22SRC.ZIP. ! 1914: ! 1915: You may obtain free copies or updates to PGP from thousands of BBS's ! 1916: worldwide or from other public sources such as Internet FTP sites. ! 1917: Don't ask me for a copy directly from me, since I'd rather avoid ! 1918: further legal problems with PKP at this time. I might be able to ! 1919: tell you where you can get it, however. ! 1920: ! 1921: After all this work I have to admit I wouldn't mind getting some fan ! 1922: mail for PGP, to gauge its popularity. Let me know what you think ! 1923: about it and how many of your friends use it. Bug reports and ! 1924: suggestions for enhancing PGP are welcome, too. Perhaps a future PGP ! 1925: release will reflect your suggestions. ! 1926: ! 1927: This project has not been funded and the project has nearly eaten me ! 1928: alive. This means you can't count on a reply to your mail, unless ! 1929: you only need a short written reply and you include a stamped ! 1930: self-addressed envelope. But I do reply to E-mail. Please keep it in ! 1931: English, as my foreign language skills are weak. If you call and I'm ! 1932: not in, it's best to just try again later. I usually don't return ! 1933: long distance phone calls, unless you leave a message that I can call ! 1934: you collect. If you need any significant amount of my time, I am ! 1935: available on a paid consulting basis, and I do return those calls. ! 1936: ! 1937: The most inconvenient mail I get is for some well-intentioned person ! 1938: to send me a few dollars asking me for a copy of PGP. I can't send ! 1939: it to them because of the legal threats from PKP (or worse-- ! 1940: sometimes these requests are from foreign countries, and I would be ! 1941: risking violating cryptographic export control laws). Even if there ! 1942: were no legal hassles involved in sending PGP to them, they usually ! 1943: don't send enough money to make it worth my time ($50 might be worth ! 1944: my time if I were actually selling this stuff). I'm just not set up ! 1945: as a low cost low volume mail order business. I can't just ignore ! 1946: the request and keep the money, because they probably regard the ! 1947: money as a fee for me to fulfill their request. If I return the ! 1948: money, I might have to get in my car and drive down to the post ! 1949: office and buy some postage stamps, because these requests rarely ! 1950: include a stamped self-addressed envelope. And I have to take the ! 1951: time to write a polite reply that I can't do it. If I postpone the ! 1952: reply and set the letter down on my desk, it might be buried within ! 1953: minutes and won't see the light of day again for months. Multiply ! 1954: these minor inconveniences by the number of requests I get, and you ! 1955: can see the problem. Isn't it enough that the software is free? It ! 1956: would be nicer if people could try to get PGP from any of the myriad ! 1957: other sources. If you don't have a modem, ask a friend to get it for ! 1958: you. If you can't find it yourself, I don't mind answering a quick ! 1959: phone call. ! 1960: ! 1961: If anyone wants to volunteer to improve PGP, please let me know. It ! 1962: could certainly use some more work. Some features were deferred to ! 1963: get it out the door. A number of PGP users have since donated their ! 1964: time to port PGP to Unix on Sun SPARCstations, to Ultrix, to VAX/VMS, ! 1965: to OS/2, to the Amiga, and to the Atari ST. Perhaps you can help ! 1966: port it to some new environments. But please let me know if you plan ! 1967: to port or add enhancements to PGP, to avoid duplication of effort, ! 1968: and to avoid starting with an obsolete version of the source code. ! 1969: ! 1970: Because so many foreign language translations of PGP have been ! 1971: produced, most of them are not distributed with the regular PGP ! 1972: release package because it would require too much disk space. ! 1973: Separate language translation "kits" are available from a number of ! 1974: independent sources, and are sometimes available separately from the ! 1975: same distribution centers that carry the regular PGP release ! 1976: software. These kits include translated versions of the file ! 1977: LANGUAGE.TXT, PGP.HLP, and the PGP User's Guide. If you want to ! 1978: produce a translation for your own native language, contact me first ! 1979: to get the latest information and standard guidelines, and to find ! 1980: out if it's been translated to your language already. Colin Plumb ! 1981: ([email protected]) maintains a comprehensive collection of foreign ! 1982: language kits from other translators. ! 1983: ! 1984: Future versions of PGP may have to change the data formats for ! 1985: messages, signatures, keys and key rings, in order to provide ! 1986: important new features. This may cause backward compatibility ! 1987: problems with this version of PGP. Future releases may provide ! 1988: conversion utilities to convert old keys, but you may have to dispose ! 1989: of old messages created with the old PGP. ! 1990: ! 1991: If you have access to the Internet, watch for announcements of new ! 1992: releases of PGP on the Internet newsgroups "sci.crypt" and PGP's own ! 1993: newsgroup, "alt.security.pgp". There is also an interest group ! 1994: mailing list called info-pgp, which is intended for users without ! 1995: access to the "alt.security.pgp" newsgroup. Info-pgp is moderated by ! 1996: Hugh Miller, and you may subscribe to it by writing him a letter at ! 1997: [email protected]. Include your name and Internet ! 1998: address. If you want to know where to get PGP, Hugh can send you a ! 1999: list of Internet FTP sites and BBS phone numbers. Hugh may also be ! 2000: reached at [email protected]. ! 2001: ! 2002: ! 2003: ! 2004: Export Controls ! 2005: --------------- ! 2006: ! 2007: The Government has made it illegal in many cases to export good ! 2008: cryptographic technology, and that may include PGP. They regard this ! 2009: kind of software as munitions. This is determined by volatile State ! 2010: Department policies, not fixed laws. I will not export this software ! 2011: out of the US or Canada in cases when it is illegal to do so under US ! 2012: State Department policies, and I assume no responsibility for other ! 2013: people exporting it on their own. ! 2014: ! 2015: If you live outside the US or Canada, I advise you not to violate US ! 2016: State Department policies by getting PGP from a US source. Since ! 2017: thousands of domestic users got it after its initial publication, it ! 2018: somehow leaked out of the US and spread itself widely abroad, like ! 2019: dandelion seeds blowing in the wind. If PGP has already found its ! 2020: way into your country, then I don't think you're violating US export ! 2021: law if you pick it up from a source outside of the US. ! 2022: ! 2023: It seems to some legal observers I've talked with, that the framers of ! 2024: the US export controls never envisioned that they would ever apply to ! 2025: cryptographic freeware that has been published and scattered to the ! 2026: winds. It's hard to imagine a US attorney trying to build a real ! 2027: case against someone for the "export" of software published freely in ! 2028: the US. As far as anyone I've talked to knows, it's never been done, ! 2029: despite numerous examples of export violations. I'm not a lawyer and ! 2030: I'm not giving you legal advice-- I'm just trying to point out what ! 2031: seems like common sense. ! 2032: ! 2033: Starting with PGP version 2.0, the release point of the software has ! 2034: been outside the US, on publicly-accessible computers in Europe. ! 2035: Each release is electronically sent back into the US and posted on ! 2036: publicly-accessible computers in the US by PGP privacy activists in ! 2037: foreign countries. There are some restrictions in the US regarding ! 2038: the import of munitions, but I'm not aware of any cases where this ! 2039: was ever enforced for importing cryptographic software into the US. ! 2040: I imagine that a legal action of that type would be quite a spectacle ! 2041: of controversy. ! 2042: ! 2043: Some foreign governments impose serious penalties on anyone inside ! 2044: their country for merely using encrypted communications. In some ! 2045: countries they might even shoot you for that. But if you live in ! 2046: that kind of country, perhaps you need PGP even more. ! 2047: ! 2048: ! 2049: ! 2050: Computer-Related Political Groups ! 2051: ================================= ! 2052: ! 2053: PGP is a very political piece of software. It seems appropriate to ! 2054: mention here some computer-related activist groups. Full details on ! 2055: these groups, and how to join them, is provided in a separate ! 2056: document file in the PGP release package. ! 2057: ! 2058: The Electronic Frontier Foundation (EFF) was founded in July, 1990, ! 2059: to assure freedom of expression in digital media, with a particular ! 2060: emphasis on applying the principles embodied in the Constitution and ! 2061: the Bill of Rights to computer-based communication. They can be ! 2062: reached at: Electronic Frontier Foundation, 238 Main Street, ! 2063: Cambridge, MA 02142, USA. ! 2064: ! 2065: The League for Programming Freedom (LPF) is a grass-roots organization ! 2066: of professors, students, businessmen, programmers and users dedicated ! 2067: to bringing back the freedom to write programs. They regard patents ! 2068: on computer algorithms as harmful to the US software industry. They ! 2069: can be reached at (617) 433-7071, or send Internet mail to ! 2070: [email protected] ! 2071: ! 2072: Computer Professionals For Social Responsibility (CPSR) empowers ! 2073: computer professionals and computer users to advocate for the ! 2074: responsible use of information technology and empowers all who use ! 2075: computer technology to participate in public policy debates on the ! 2076: impacts of computers on society. They can be reached at: ! 2077: 415-322-3778 in Palo Alto, E-mail address [email protected]. ! 2078: ! 2079: For more details on these groups, see the accompanying document in ! 2080: the PGP release package. ! 2081: ! 2082: ! 2083: Recommended Introductory Readings ! 2084: ================================= ! 2085: ! 2086: 1) Dorothy Denning, "Cryptography and Data Security", Addison-Wesley, ! 2087: Reading, MA 1982 ! 2088: 2) Dorothy Denning, "Protecting Public Keys and Signature Keys", ! 2089: IEEE Computer, Feb 1983 ! 2090: 3) Martin E. Hellman, "The Mathematics of Public-Key Cryptography," ! 2091: Scientific American, Aug 1979 ! 2092: ! 2093: Other Readings ! 2094: ============== ! 2095: ! 2096: 4) Ronald Rivest, "The MD5 Message Digest Algorithm", MIT Laboratory ! 2097: for Computer Science, 1991 ! 2098: 5) Xuejia Lai, "On the Design and Security of Block Ciphers", ! 2099: Institute for Signal and Information Processing, ETH-Zentrum, ! 2100: Zurich, Switzerland, 1992 ! 2101: 6) Xuejia Lai, James L. Massey, Sean Murphy, "Markov Ciphers and ! 2102: Differential Cryptanalysis", Advances in Cryptology- EUROCRYPT'91 ! 2103: 7) Philip Zimmermann, "A Proposed Standard Format for RSA ! 2104: Cryptosystems", Advances in Computer Security, Vol III, edited by ! 2105: Rein Turn, Artech House, 1988 ! 2106: 8) Paul Wallich, "Electronic Envelopes", Scientific American, Feb ! 2107: 1993, pages 30-32. (This is an article on PGP) ! 2108: ! 2109: ! 2110: To Contact the Author ! 2111: ===================== ! 2112: ! 2113: Philip Zimmermann may be reached at: ! 2114: ! 2115: Boulder Software Engineering ! 2116: 3021 Eleventh Street ! 2117: Boulder, Colorado 80304 USA ! 2118: Phone 303-541-0140 (voice or FAX) (10:00am - 7:00pm Mountain Time) ! 2119: Internet: [email protected] ! 2120: ! 2121: ! 2122: ! 2123: Appendix A: Where to Get PGP ! 2124: ============================= ! 2125: ! 2126: The following describes how to get the freeware public key ! 2127: cryptographic software PGP (Pretty Good Privacy) from an anonymous ! 2128: FTP site on Internet, or from other sources. ! 2129: ! 2130: PGP has sophisticated key management, an RSA/conventional hybrid ! 2131: encryption scheme, message digests for digital signatures, data ! 2132: compression before encryption, and good ergonomic design. PGP is ! 2133: well featured and fast, and has excellent user documentation. Source ! 2134: code is free. ! 2135: ! 2136: PGP uses the RSA cryptosystem which is claimed by a US patent held by ! 2137: a company called Public Key Partners. PGP users outside the US take ! 2138: note that there is no RSA patent outside the US. Also, bear in mind ! 2139: that there are US and Canadian export laws prohibiting anyone inside ! 2140: the US and Canada from exporting cryptographic software like this. ! 2141: If you live outside the US, you're probably not violating US export ! 2142: law if you pick it up from a source outside of the US. ! 2143: ! 2144: What follows is a small sample of places that allegedly have PGP, as ! 2145: of 2 March 1993. This information is not guaranteed to be correct. ! 2146: Some US sites have occasionally withdrawn PGP because of fear of ! 2147: legal intimidation from the RSA patent holders. ! 2148: ! 2149: There are two compressed archive files in the PGP 2.2 MSDOS release. ! 2150: You must get pgp22.zip which contains the MSDOS binary executable and ! 2151: the PGP User's Guide, and you can optionally get pgp22src.zip which ! 2152: contains the source files. These files can be decompressed with the ! 2153: MSDOS shareware archive decompression utility PKUNZIP.EXE, version ! 2154: 1.1 or later. For Unix users who lack an implementation of UNZIP, ! 2155: the source code can also be found in the compressed tar file ! 2156: pgp22src.tar.Z. ! 2157: ! 2158: A reminder: Set mode to binary or image when doing an FTP transfer. ! 2159: And when doing a kermit download to your PC, specify 8-bit binary ! 2160: mode at both ends. Here are some Internet sites that have PGP via ! 2161: anonymous FTP: ! 2162: ! 2163: Finland: nic.funet.fi (128.214.6.100) ! 2164: Directory: /pub/unix/security/crypt/ ! 2165: ! 2166: Italy: ghost.dsi.unimi.it (149.132.2.1) ! 2167: Directory: /pub/security/ ! 2168: ! 2169: UK: src.doc.ic.ac.uk ! 2170: Directory: /computing/security/software/PGP ! 2171: ! 2172: For those lacking FTP connectivity to the net, nic.funet.fi also ! 2173: offers the files via email. Send the following mail message to ! 2174: [email protected]: ! 2175: ! 2176: ENCODER uuencode ! 2177: SEND pub/unix/security/crypt/pgp22src.zip ! 2178: SEND pub/unix/security/crypt/pgp22.zip ! 2179: ! 2180: This will deposit the two zipfiles, as (about) 15 batched messages in ! 2181: your mailbox within about 24 hours. Save and uudecode. ! 2182: ! 2183: In the US, PGP may be found on God knows how many BBS systems, far ! 2184: too many to list here. Still, if you don't have any local BBS phone ! 2185: numbers handy, here are some BBS's you might try. ! 2186: ! 2187: The GRAPEVINE BBS in Little Rock Arkansas has set up a special ! 2188: account for people to download PGP for free. The SYSOP is Jim Wenzel, ! 2189: at [email protected]. The following phone numbers are ! 2190: applicable and should be dialed in the order presented (i.e., the ! 2191: first one is the highest speed line): (501) 753-6859, (501) ! 2192: 753-8121, (501) 791-0124. When asked to login use the following ! 2193: information: ! 2194: ! 2195: name: PGP USER ('PGP' is 1st name, 'USER' is 2nd name) ! 2196: password: PGP ! 2197: ! 2198: The Northern Lights BBS in Troy, NY, has PGP for free download. It ! 2199: is run by Daniel Ray. Call (518) 237-2163 at 300-2400 bps 8N1. Then ! 2200: login directly to the pgp account as follows: ! 2201: ! 2202: tnllogin: pgp ! 2203: Password: key ! 2204: ! 2205: In Colorado, try this single-line BBS: 303 443-8292. It is often ! 2206: busy, so keep trying. Log in with your own name. ! 2207: ! 2208: PGP is also widely available on Fidonet, a large informal network of ! 2209: PC-based bulletin board systems interconnected via modems. Check ! 2210: your local bulletin board systems. It is available on many foreign ! 2211: and domestic Fidonet BBS sites. ! 2212: ! 2213: In New Zealand, try this (supposedly free) dial-up BBS system: ! 2214: Kappa Crucis: +64 9 817-3714, -3725, -3324, -8424, -3094, -3393 ! 2215: ! 2216: For information on PGP implementations on the Apple Macintosh, ! 2217: Commodore Amiga, or Atari ST, or any other questions about where to ! 2218: get PGP for any other platform, contact Hugh Miller at ! 2219: [email protected]. ! 2220: ! 2221: Here are a few people and their email addresses or phone numbers you ! 2222: can contact in some countries to get information on local PGP ! 2223: availability: ! 2224: ! 2225: Peter Gutmann Hugh Kennedy ! 2226: [email protected] [email protected] ! 2227: New Zealand Germany ! 2228: ! 2229: Branko Lankester Miguel Angel Gallardo ! 2230: [email protected] [email protected] ! 2231: +31 2159 42242 (341) 474 38 09 ! 2232: The Netherlands Spain ! 2233: ! 2234: Hugh Miller Colin Plumb ! 2235: [email protected] [email protected] ! 2236: (312) 508-2727 Toronto, Ontario, Canada ! 2237: USA ! 2238: ! 2239: Jean-loup Gailly ! 2240: [email protected] ! 2241: France ! 2242:
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