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1.1.1.3 ! root 1: ! 2: Phil's Pretty Good Software ! 3: Presents ! 4: ! 5: ======= ! 6: PGP(tm) ! 7: ======= ! 8: ! 9: Pretty Good(tm) Privacy ! 10: Public Key Encryption for the Masses ! 11: ! 12: ! 13: ------------------------- ! 14: PGP(tm) User's Guide ! 15: Volume I: Essential Topics ! 16: -------------------------- ! 17: by Philip Zimmermann ! 18: Revised 7 May 94 ! 19: ! 20: ! 21: PGP Version 2.5 - 7 May 94 ! 22: Software by ! 23: Philip Zimmermann, and many others. ! 24: ! 25: ! 26: ! 27: ! 28: Synopsis: PGP(tm) uses public-key encryption to protect E-mail and ! 29: data files. Communicate securely with people you've never met, with ! 30: no secure channels needed for prior exchange of keys. PGP is well ! 31: featured and fast, with sophisticated key management, digital ! 32: signatures, data compression, and good ergonomic design. ! 33: ! 34: ! 35: Software and documentation (c) Copyright 1990-1994 Philip Zimmermann. ! 36: All rights reserved. For information on PGP licensing, distribution, ! 37: copyrights, patents, trademarks, liability limitations, and export ! 38: controls, see the "Legal Issues" section in the "PGP User's Guide, ! 39: Volume II: Special Topics". Distributed by the Massachusetts ! 40: Institute of Technology. ! 41: ! 42: ! 43: "Whatever you do will be insignificant, but it is very important that ! 44: you do it." --Mahatma Gandhi ! 45: ! 46: ! 47: Contents ! 48: ======== ! 49: ! 50: Quick Overview ! 51: Why Do You Need PGP? ! 52: How it Works ! 53: Installing PGP ! 54: How to Use PGP ! 55: To See a Usage Summary ! 56: Encrypting a Message ! 57: Encrypting a Message to Multiple Recipients ! 58: Signing a Message ! 59: Signing and then Encrypting ! 60: Using Just Conventional Encryption ! 61: Decrypting and Checking Signatures ! 62: Managing Keys ! 63: RSA Key Generation ! 64: Adding a Key to Your Key Ring ! 65: Removing a Key or User ID from Your Key Ring ! 66: Extracting (copying) a Key from Your Key Ring ! 67: Viewing the Contents of Your Key Ring ! 68: How to Protect Public Keys from Tampering ! 69: How Does PGP Keep Track of Which Keys are Valid? ! 70: How to Protect Secret Keys from Disclosure ! 71: Revoking a Public Key ! 72: What If You Lose Your Secret Key? ! 73: Advanced Topics ! 74: Sending Ciphertext Through E-mail Channels: Radix-64 Format ! 75: Environmental Variable for Path Name ! 76: Setting Configuration Parameters: CONFIG.TXT ! 77: Vulnerabilities ! 78: Beware of Snake Oil ! 79: PGP Quick Reference ! 80: Legal Issues ! 81: Acknowledgments ! 82: About the Author ! 83: ! 84: ! 85: Quick Overview ! 86: ============== ! 87: ! 88: Pretty Good(tm) Privacy (PGP), from Phil's Pretty Good Software, is a ! 89: high security cryptographic software application for MSDOS, Unix, ! 90: VAX/VMS, and other computers. PGP allows people to exchange files or ! 91: messages with privacy, authentication, and convenience. Privacy ! 92: means that only those intended to receive a message can read it. ! 93: Authentication means that messages that appear to be from a ! 94: particular person can only have originated from that person. ! 95: Convenience means that privacy and authentication are provided ! 96: without the hassles of managing keys associated with conventional ! 97: cryptographic software. No secure channels are needed to exchange ! 98: keys between users, which makes PGP much easier to use. This is ! 99: because PGP is based on a powerful new technology called "public key" ! 100: cryptography. ! 101: ! 102: PGP combines the convenience of the Rivest-Shamir-Adleman (RSA) ! 103: public key cryptosystem with the speed of conventional cryptography, ! 104: message digests for digital signatures, data compression before ! 105: encryption, good ergonomic design, and sophisticated key management. ! 106: And PGP performs the public-key functions faster than most other ! 107: software implementations. PGP is public key cryptography for the ! 108: masses. ! 109: ! 110: PGP does not provide any built-in modem communications capability. ! 111: You must use a separate software product for that. ! 112: ! 113: This document, "Volume I: Essential Topics", only explains the ! 114: essential concepts for using PGP, and should be read by all PGP ! 115: users. "Volume II: Special Topics" covers the advanced features of ! 116: PGP and other special topics, and may be read by more serious PGP ! 117: users. Neither volume explains the underlying technology details of ! 118: cryptographic algorithms and data structures. ! 119: ! 120: ! 121: Why Do You Need PGP? ! 122: ==================== ! 123: ! 124: It's personal. It's private. And it's no one's business but yours. ! 125: You may be planning a political campaign, discussing your taxes, or ! 126: having an illicit affair. Or you may be doing something that you ! 127: feel shouldn't be illegal, but is. Whatever it is, you don't want ! 128: your private electronic mail (E-mail) or confidential documents read ! 129: by anyone else. There's nothing wrong with asserting your privacy. ! 130: Privacy is as apple-pie as the Constitution. ! 131: ! 132: Perhaps you think your E-mail is legitimate enough that encryption is ! 133: unwarranted. If you really are a law-abiding citizen with nothing to ! 134: hide, then why don't you always send your paper mail on postcards? ! 135: Why not submit to drug testing on demand? Why require a warrant for ! 136: police searches of your house? Are you trying to hide something? ! 137: You must be a subversive or a drug dealer if you hide your mail ! 138: inside envelopes. Or maybe a paranoid nut. Do law-abiding citizens ! 139: have any need to encrypt their E-mail? ! 140: ! 141: What if everyone believed that law-abiding citizens should use ! 142: postcards for their mail? If some brave soul tried to assert his ! 143: privacy by using an envelope for his mail, it would draw suspicion. ! 144: Perhaps the authorities would open his mail to see what he's hiding. ! 145: Fortunately, we don't live in that kind of world, because everyone ! 146: protects most of their mail with envelopes. So no one draws suspicion ! 147: by asserting their privacy with an envelope. There's safety in ! 148: numbers. Analogously, it would be nice if everyone routinely used ! 149: encryption for all their E-mail, innocent or not, so that no one drew ! 150: suspicion by asserting their E-mail privacy with encryption. Think ! 151: of it as a form of solidarity. ! 152: ! 153: Today, if the Government wants to violate the privacy of ordinary ! 154: citizens, it has to expend a certain amount of expense and labor to ! 155: intercept and steam open and read paper mail, and listen to and ! 156: possibly transcribe spoken telephone conversation. This kind of ! 157: labor-intensive monitoring is not practical on a large scale. This ! 158: is only done in important cases when it seems worthwhile. ! 159: ! 160: More and more of our private communications are being routed through ! 161: electronic channels. Electronic mail is gradually replacing ! 162: conventional paper mail. E-mail messages are just too easy to ! 163: intercept and scan for interesting keywords. This can be done ! 164: easily, routinely, automatically, and undetectably on a grand scale. ! 165: International cablegrams are already scanned this way on a large ! 166: scale by the NSA. ! 167: ! 168: We are moving toward a future when the nation will be crisscrossed ! 169: with high capacity fiber optic data networks linking together all our ! 170: increasingly ubiquitous personal computers. E-mail will be the norm ! 171: for everyone, not the novelty it is today. The Government will ! 172: protect our E-mail with Government-designed encryption protocols. ! 173: Probably most people will acquiesce to that. But perhaps some people ! 174: will prefer their own protective measures. ! 175: ! 176: Senate Bill 266, a 1991 omnibus anti-crime bill, had an unsettling ! 177: measure buried in it. If this non-binding resolution had become real ! 178: law, it would have forced manufacturers of secure communications ! 179: equipment to insert special "trap doors" in their products, so that ! 180: the Government can read anyone's encrypted messages. It reads: "It ! 181: is the sense of Congress that providers of electronic communications ! 182: services and manufacturers of electronic communications service ! 183: equipment shall insure that communications systems permit the ! 184: Government to obtain the plain text contents of voice, data, and ! 185: other communications when appropriately authorized by law." This ! 186: measure was defeated after rigorous protest from civil libertarians ! 187: and industry groups. ! 188: ! 189: In 1992, the FBI Digital Telephony wiretap proposal was introduced to ! 190: Congress. It would require all manufacturers of communications ! 191: equipment to build in special remote wiretap ports that would enable ! 192: the FBI to remotely wiretap all forms of electronic communication ! 193: from FBI offices. Although it never attracted any sponsors in ! 194: Congress in 1992 because of citizen opposition, it was reintroduced in ! 195: 1994. ! 196: ! 197: Most alarming of all is the White House's bold new encryption policy ! 198: initiative, under development at NSA since the start of the Bush ! 199: administration, and unveiled April 16th, 1993. The centerpiece of ! 200: this initiative is a Government-built encryption device, called the ! 201: "Clipper" chip, containing a new classified NSA encryption ! 202: algorithm. The Government is encouraging private industry to design ! 203: it into all their secure communication products, like secure phones, ! 204: secure FAX, etc. AT&T is now putting the Clipper into their secure ! 205: voice products. The catch: At the time of manufacture, each Clipper ! 206: chip will be loaded with its own unique key, and the Government gets ! 207: to keep a copy, placed in escrow. Not to worry, though-- the ! 208: Government promises that they will use these keys to read your ! 209: traffic only when duly authorized by law. Of course, to make Clipper ! 210: completely effective, the next logical step would be to outlaw other ! 211: forms of cryptography. ! 212: ! 213: If privacy is outlawed, only outlaws will have privacy. Intelligence ! 214: agencies have access to good cryptographic technology. So do the big ! 215: arms and drug traffickers. So do defense contractors, oil companies, ! 216: and other corporate giants. But ordinary people and grassroots ! 217: political organizations mostly have not had access to affordable ! 218: "military grade" public-key cryptographic technology. Until now. ! 219: ! 220: PGP empowers people to take their privacy into their own hands. ! 221: There's a growing social need for it. That's why I wrote it. ! 222: ! 223: ! 224: How it Works ! 225: ============ ! 226: ! 227: It would help if you were already familiar with the concept of ! 228: cryptography in general and public key cryptography in particular. ! 229: Nonetheless, here are a few introductory remarks about public key ! 230: cryptography. ! 231: ! 232: First, some elementary terminology. Suppose I want to send you a ! 233: message, but I don't want anyone but you to be able to read it. I ! 234: can "encrypt", or "encipher" the message, which means I scramble it ! 235: up in a hopelessly complicated way, rendering it unreadable to anyone ! 236: except you, the intended recipient of the message. I supply a ! 237: cryptographic "key" to encrypt the message, and you have to use the ! 238: same key to decipher or "decrypt" it. At least that's how it works ! 239: in conventional "single-key" cryptosystems. ! 240: ! 241: In conventional cryptosystems, such as the US Federal Data Encryption ! 242: Standard (DES), a single key is used for both encryption and ! 243: decryption. This means that a key must be initially transmitted via ! 244: secure channels so that both parties can know it before encrypted ! 245: messages can be sent over insecure channels. This may be ! 246: inconvenient. If you have a secure channel for exchanging keys, then ! 247: why do you need cryptography in the first place? ! 248: ! 249: In public key cryptosystems, everyone has two related complementary ! 250: keys, a publicly revealed key and a secret key. Each key unlocks the ! 251: code that the other key makes. Knowing the public key does not help ! 252: you deduce the corresponding secret key. The public key can be ! 253: published and widely disseminated across a communications network. ! 254: This protocol provides privacy without the need for the same kind of ! 255: secure channels that a conventional cryptosystem requires. ! 256: ! 257: Anyone can use a recipient's public key to encrypt a message to that ! 258: person, and that recipient uses her own corresponding secret key to ! 259: decrypt that message. No one but the recipient can decrypt it, ! 260: because no one else has access to that secret key. Not even the ! 261: person who encrypted the message can decrypt it. ! 262: ! 263: Message authentication is also provided. The sender's own secret key ! 264: can be used to encrypt a message, thereby "signing" it. This creates ! 265: a digital signature of a message, which the recipient (or anyone ! 266: else) can check by using the sender's public key to decrypt it. This ! 267: proves that the sender was the true originator of the message, and ! 268: that the message has not been subsequently altered by anyone else, ! 269: because the sender alone possesses the secret key that made that ! 270: signature. Forgery of a signed message is infeasible, and the sender ! 271: cannot later disavow his signature. ! 272: ! 273: These two processes can be combined to provide both privacy and ! 274: authentication by first signing a message with your own secret key, ! 275: then encrypting the signed message with the recipient's public key. ! 276: The recipient reverses these steps by first decrypting the message ! 277: with her own secret key, then checking the enclosed signature with ! 278: your public key. These steps are done automatically by the ! 279: recipient's software. ! 280: ! 281: Because the public key encryption algorithm is much slower than ! 282: conventional single-key encryption, encryption is better accomplished ! 283: by using a high-quality fast conventional single-key encryption ! 284: algorithm to encipher the message. This original unenciphered ! 285: message is called "plaintext". In a process invisible to the user, a ! 286: temporary random key, created just for this one "session", is used to ! 287: conventionally encipher the plaintext file. Then the recipient's ! 288: public key is used to encipher this temporary random conventional ! 289: key. This public-key-enciphered conventional "session" key is sent ! 290: along with the enciphered text (called "ciphertext") to the ! 291: recipient. The recipient uses her own secret key to recover this ! 292: temporary session key, and then uses that key to run the fast ! 293: conventional single-key algorithm to decipher the large ciphertext ! 294: message. ! 295: ! 296: Public keys are kept in individual "key certificates" that include ! 297: the key owner's user ID (which is that person's name), a timestamp of ! 298: when the key pair was generated, and the actual key material. Public ! 299: key certificates contain the public key material, while secret key ! 300: certificates contain the secret key material. Each secret key is ! 301: also encrypted with its own password, in case it gets stolen. A key ! 302: file, or "key ring" contains one or more of these key certificates. ! 303: Public key rings contain public key certificates, and secret key ! 304: rings contain secret key certificates. ! 305: ! 306: The keys are also internally referenced by a "key ID", which is an ! 307: "abbreviation" of the public key (the least significant 64 bits of ! 308: the large public key). When this key ID is displayed, only the lower ! 309: 32 bits are shown for further brevity. While many keys may share the ! 310: same user ID, for all practical purposes no two keys share the same ! 311: key ID. ! 312: ! 313: PGP uses "message digests" to form signatures. A message digest is a ! 314: 128-bit cryptographically strong one-way hash function of the ! 315: message. It is somewhat analogous to a "checksum" or CRC error ! 316: checking code, in that it compactly "represents" the message and is ! 317: used to detect changes in the message. Unlike a CRC, however, it is ! 318: computationally infeasible for an attacker to devise a substitute ! 319: message that would produce an identical message digest. The message ! 320: digest gets encrypted by the secret key to form a signature. ! 321: ! 322: Documents are signed by prefixing them with signature certificates, ! 323: which contain the key ID of the key that was used to sign it, a ! 324: secret-key-signed message digest of the document, and a timestamp of ! 325: when the signature was made. The key ID is used by the receiver to ! 326: look up the sender's public key to check the signature. The ! 327: receiver's software automatically looks up the sender's public key ! 328: and user ID in the receiver's public key ring. ! 329: ! 330: Encrypted files are prefixed by the key ID of the public key used to ! 331: encrypt them. The receiver uses this key ID message prefix to look ! 332: up the secret key needed to decrypt the message. The receiver's ! 333: software automatically looks up the necessary secret decryption key ! 334: in the receiver's secret key ring. ! 335: ! 336: These two types of key rings are the principal method of storing and ! 337: managing public and secret keys. Rather than keep individual keys in ! 338: separate key files, they are collected in key rings to facilitate the ! 339: automatic lookup of keys either by key ID or by user ID. Each user ! 340: keeps his own pair of key rings. An individual public key is ! 341: temporarily kept in a separate file long enough to send to your ! 342: friend who will then add it to her key ring. ! 343: ! 344: ! 345: ! 346: Installing PGP ! 347: ============== ! 348: ! 349: The MSDOS PGP 2.5 release comes in a compressed archive file called ! 350: PGP25.ZIP (each new release will have a name in the form "PGPxy.ZIP" ! 351: for PGP version number x.y). The archive can be decompressed with ! 352: the MSDOS shareware decompression utility PKUNZIP, or the Unix ! 353: utility "unzip". The PGP release package contains a README.DOC file ! 354: that you should always read before installing PGP. This README.DOC ! 355: file contains late-breaking news on what's new in this release of ! 356: PGP, as well as information on what's in all the other files included ! 357: in the release. ! 358: ! 359: If you already have PGP version 1.0 for MSDOS, you should probably ! 360: delete it, because no one else uses it anymore. If you don't want to ! 361: delete it, rename the old executable file to pgp1.exe, to avoid name ! 362: conflicts with the new PGP. ! 363: ! 364: To install PGP on your MSDOS system, you just have to copy the ! 365: compressed archive PGPxx.ZIP file into a suitable directory on your ! 366: hard disk (like C:\PGP), and decompress it with PKUNZIP. For best ! 367: results, you will also modify your AUTOEXEC.BAT file, as described ! 368: elsewhere in this manual, but you can do that later, after you've ! 369: played with PGP a bit and read more of this manual. If you haven't ! 370: run PGP before, the first step after installation (and reading this ! 371: manual) is to run the PGP key generation command "pgp -kg". ! 372: ! 373: Installing on Unix and VAX/VMS is generally similar to installing on ! 374: MSDOS, but you may have to compile the source code first. A Unix ! 375: makefile is provided with the source release for this purpose. ! 376: ! 377: For further details on installation, see the separate PGP ! 378: Installation Guide, in the file SETUP.DOC included with this ! 379: release. It fully describes how to set up the PGP directory and your ! 380: AUTOEXEC.BAT file and how to use PKUNZIP to install it. ! 381: ! 382: ! 383: ! 384: How to Use PGP ! 385: ============== ! 386: ! 387: ! 388: To See a Usage Summary ! 389: ---------------------- ! 390: ! 391: To see a quick command usage summary for PGP, just type: ! 392: ! 393: pgp -h ! 394: ! 395: ! 396: ! 397: Encrypting a Message ! 398: -------------------- ! 399: ! 400: To encrypt a plaintext file with the recipient's public key, type: ! 401: ! 402: pgp -e textfile her_userid ! 403: ! 404: This command produces a ciphertext file called textfile.pgp. A ! 405: specific example is: ! 406: ! 407: pgp -e letter.txt Alice ! 408: or: ! 409: pgp -e letter.txt "Alice S" ! 410: ! 411: The first example searches your public key ring file "pubring.pgp" ! 412: for any public key certificates that contain the string "Alice" ! 413: anywhere in the user ID field. The second example would find any ! 414: user IDs that contain "Alice S". You can't use spaces in the string ! 415: on the command line unless you enclose the whole string in quotes. ! 416: The search is not case-sensitive. If it finds a matching public key, ! 417: it uses it to encrypt the plaintext file "letter.txt", producing a ! 418: ciphertext file called "letter.pgp". ! 419: ! 420: PGP attempts to compress the plaintext before encrypting it, thereby ! 421: greatly enhancing resistance to cryptanalysis. Thus the ciphertext ! 422: file will likely be smaller than the plaintext file. ! 423: ! 424: If you want to send this encrypted message through E-mail channels, ! 425: convert it into printable ASCII "radix-64" format by adding the -a ! 426: option, as described later. ! 427: ! 428: ! 429: ! 430: Encrypting a Message to Multiple Recipients ! 431: ------------------------------------------- ! 432: ! 433: If you want to send the same message to more than one person, you may ! 434: specify encryption for several recipients, any of whom may decrypt the ! 435: same ciphertext file. To specify multiple recipients, just add more ! 436: user IDs to the command line, like so: ! 437: ! 438: pgp -e letter.txt Alice Bob Carol ! 439: ! 440: This would create a ciphertext file called letter.pgp that could be ! 441: decrypted by Alice or Bob or Carol. Any number of recipients may be ! 442: specified. ! 443: ! 444: ! 445: ! 446: Signing a Message ! 447: ----------------- ! 448: ! 449: To sign a plaintext file with your secret key, type: ! 450: ! 451: pgp -s textfile [-u your_userid] ! 452: ! 453: Note that [brackets] denote an optional field, so don't actually type ! 454: real brackets. ! 455: ! 456: This command produces a signed file called textfile.pgp. A specific ! 457: example is: ! 458: ! 459: pgp -s letter.txt -u Bob ! 460: ! 461: This searches your secret key ring file "secring.pgp" for any secret ! 462: key certificates that contain the string "Bob" anywhere in the user ! 463: ID field. The search is not case-sensitive. If it finds a matching ! 464: secret key, it uses it to sign the plaintext file "letter.txt", ! 465: producing a signature file called "letter.pgp". ! 466: ! 467: If you leave off the user ID field, the first key on your secret ! 468: key ring is used as the default secret key for your signature. ! 469: ! 470: Probably the most convenient way to sign an E-mail message with PGP ! 471: is to use the CLEARSIG feature, explained later. This allows the ! 472: signature to be applied in printable form at the end of the text, and ! 473: the text is still readable by the recipient without having to use ! 474: PGP. This is explained in detail in the section entitled "CLEARSIG - ! 475: Enable Signed Messages to be Encapsulated as Clear Text", in the ! 476: Special Topics volume. If you can't wait to read that section of the ! 477: manual, you can see how an E-mail message signed this way would look, ! 478: with this example: ! 479: ! 480: pgp -sta message.txt ! 481: ! 482: This would create a signed message in file "message.asc", comprised ! 483: of the original text, still human-readable, appended with a printable ! 484: ASCII signature certificate, ready to send through an E-mail system. ! 485: This example assumes that you are using the normal settings for the ! 486: CLEARSIG flag in the config file. ! 487: ! 488: ! 489: Signing and then Encrypting ! 490: --------------------------- ! 491: ! 492: To sign a plaintext file with your secret key, and then encrypt it ! 493: with the recipient's public key: ! 494: ! 495: pgp -es textfile her_userid [-u your_userid] ! 496: ! 497: Note that [brackets] denote an optional field, so don't actually type ! 498: real brackets. ! 499: ! 500: This example produces a nested ciphertext file called textfile.pgp. ! 501: Your secret key to create the signature is automatically looked up in ! 502: your secret key ring via your_userid. Her public encryption key is ! 503: automatically looked up in your public key ring via her_userid. If ! 504: you leave off her user ID field from the command line, you will be ! 505: prompted for it. ! 506: ! 507: If you leave off your own user ID field, the first key on your secret ! 508: key ring is be used as the default secret key for your signature. ! 509: ! 510: Note that PGP attempts to compress the plaintext before encrypting ! 511: it. ! 512: ! 513: If you want to send this encrypted message through E-mail channels, ! 514: convert it into printable ASCII "radix-64" format by adding the -a ! 515: option, as described later. ! 516: ! 517: Multiple recipients may be specified by adding more user IDs to the ! 518: command line. ! 519: ! 520: ! 521: ! 522: Using Just Conventional Encryption ! 523: ---------------------------------- ! 524: ! 525: Sometimes you just need to encrypt a file the old-fashioned way, with ! 526: conventional single-key cryptography. This approach is useful for ! 527: protecting archive files that will be stored but will not be sent to ! 528: anyone else. Since the same person that encrypted the file will also ! 529: decrypt the file, public key cryptography is not really necessary. ! 530: ! 531: To encrypt a plaintext file with just conventional cryptography, ! 532: type: ! 533: ! 534: pgp -c textfile ! 535: ! 536: This example encrypts the plaintext file called textfile, producing a ! 537: ciphertext file called textfile.pgp, without using public key ! 538: cryptography, key rings, user IDs, or any of that stuff. It prompts ! 539: you for a pass phrase to use as a conventional key to encipher the ! 540: file. This pass phrase need not be (and, indeed, SHOULD not be) the ! 541: same pass phrase that you use to protect your own secret key. Note ! 542: that PGP attempts to compress the plaintext before encrypting it. ! 543: ! 544: PGP will not encrypt the same plaintext the same way twice, even if ! 545: you used the same pass phrase every time. ! 546: ! 547: ! 548: ! 549: Decrypting and Checking Signatures ! 550: ---------------------------------- ! 551: ! 552: To decrypt an encrypted file, or to check the signature integrity of a ! 553: signed file: ! 554: ! 555: pgp ciphertextfile [-o plaintextfile] ! 556: ! 557: Note that [brackets] denote an optional field, so don't actually type ! 558: real brackets. ! 559: ! 560: The ciphertext file name is assumed to have a default extension of ! 561: ".pgp". The optional plaintext output file name specifies where to ! 562: put processed plaintext output. If no name is specified, the ! 563: ciphertext filename is used, with no extension. If a signature is ! 564: nested inside of an encrypted file, it is automatically decrypted and ! 565: the signature integrity is checked. The full user ID of the signer ! 566: is displayed. ! 567: ! 568: Note that the "unwrapping" of the ciphertext file is completely ! 569: automatic, regardless of whether the ciphertext file is just signed, ! 570: just encrypted, or both. PGP uses the key ID prefix in the ! 571: ciphertext file to automatically find the appropriate secret ! 572: decryption key on your secret key ring. If there is a nested ! 573: signature, PGP then uses the key ID prefix in the nested signature to ! 574: automatically find the appropriate public key on your public key ring ! 575: to check the signature. If all the right keys are already present on ! 576: your key rings, no user intervention is required, except that you ! 577: will be prompted for your password for your secret key if necessary. ! 578: If the ciphertext file was conventionally encrypted without public ! 579: key cryptography, PGP recognizes this and prompts you for the pass ! 580: phrase to conventionally decrypt it. ! 581: ! 582: ! 583: Managing Keys ! 584: ============= ! 585: ! 586: Since the time of Julius Caesar, key management has always been the ! 587: hardest part of cryptography. One of the principal distinguishing ! 588: features of PGP is its sophisticated key management. ! 589: ! 590: ! 591: ! 592: RSA Key Generation ! 593: ------------------ ! 594: ! 595: To generate your own unique public/secret key pair of a specified ! 596: size, type: ! 597: ! 598: pgp -kg ! 599: ! 600: PGP shows you a menu of recommended key sizes (casual grade, ! 601: commercial grade, or "military" grade) and prompts you for what size ! 602: key you want, up to around a thousand bits. The bigger the key, the ! 603: more security you get, but you pay a price in speed. ! 604: ! 605: It also asks for a user ID, which means your name. It's a good idea ! 606: to use your full name as your user ID, because then there is less ! 607: risk of other people using the wrong public key to encrypt messages ! 608: to you. Spaces and punctuation are allowed in the user ID. It would ! 609: help if you put your E-mail address in <angle brackets> after your ! 610: name, like so: ! 611: ! 612: Robert M. Smith <[email protected]> ! 613: ! 614: If you don't have an E-mail address, use your phone number or some ! 615: other unique information that would help ensure that your user ID is ! 616: unique. ! 617: ! 618: PGP also asks for a "pass phrase" to protect your secret key in case ! 619: it falls into the wrong hands. Nobody can use your secret key file ! 620: without this pass phrase. The pass phrase is like a password, except ! 621: that it can be a whole phrase or sentence with many words, spaces, ! 622: punctuation, or anything else you want in it. Don't lose this pass ! 623: phrase-- there's no way to recover it if you do lose it. This pass ! 624: phrase will be needed later every time you use your secret key. The ! 625: pass phrase is case-sensitive, and should not be too short or easy to ! 626: guess. It is never displayed on the screen. Don't leave it written ! 627: down anywhere where someone else can see it, and don't store it on ! 628: your computer. If you don't want a pass phrase (You fool!), just ! 629: press return (or enter) at the pass phrase prompt. ! 630: ! 631: The public/secret key pair is derived from large truly random numbers ! 632: derived mainly from measuring the intervals between your keystrokes ! 633: with a fast timer. The software will ask you to enter some random ! 634: text to help it accumulate some random bits for the keys. When ! 635: asked, you should provide some keystrokes that are reasonably random ! 636: in their timing, and it wouldn't hurt to make the actual characters ! 637: that you type irregular in content as well. Some of the randomness ! 638: is derived from the unpredictability of the content of what you ! 639: type. So don't just type repeated sequences of characters. ! 640: ! 641: Note that RSA key generation is a lengthy process. It may take a few ! 642: seconds for a small key on a fast processor, or quite a few minutes ! 643: for a large key on an old IBM PC/XT. ! 644: ! 645: The generated key pair will be placed on your public and secret key ! 646: rings. You can later use the -kx command option to extract (copy) ! 647: your new public key from your public key ring and place it in a ! 648: separate public key file suitable for distribution to your friends. ! 649: The public key file can be sent to your friends for inclusion in ! 650: their public key rings. Naturally, you keep your secret key file to ! 651: yourself, and you should include it on your secret key ring. Each ! 652: secret key on a key ring is individually protected with its own pass ! 653: phrase. ! 654: ! 655: Never give your secret key to anyone else. For the same reason, don't ! 656: make key pairs for your friends. Everyone should make their own key ! 657: pair. Always keep physical control of your secret key, and don't risk ! 658: exposing it by storing it on a remote timesharing computer. Keep it ! 659: on your own personal computer. ! 660: ! 661: ! 662: ! 663: Adding a Key to Your Key Ring ! 664: ----------------------------- ! 665: ! 666: To add a public or secret key file's contents to your public or ! 667: secret key ring (note that [brackets] denote an optional field): ! 668: ! 669: pgp -ka keyfile [keyring] ! 670: ! 671: The keyfile extension defaults to ".pgp". The optional keyring file ! 672: name defaults to "pubring.pgp" or "secring.pgp", depending on whether ! 673: the keyfile contains a public or a secret key. You may specify a ! 674: different key ring file name, with the extension defaulting to ! 675: ".pgp". ! 676: ! 677: If the key is already on your key ring, PGP will not add it again. ! 678: All of the keys in the keyfile are added to the keyring, except for ! 679: duplicates. If the key being added has attached signatures ! 680: certifying it, the signatures are added with the key. If the key is ! 681: already on your key ring, PGP just merges in any new certifying ! 682: signatures for that key that you don't already have on your key ring. ! 683: ! 684: PGP was originally designed for handling small personal keyrings. If ! 685: you want to handle really big keyrings, see the section on "Handling ! 686: Large Public Keyrings" in the Special Topics volume. ! 687: ! 688: ! 689: ! 690: Removing a Key or User ID from Your Key Ring ! 691: -------------------------------------------- ! 692: ! 693: To remove a key or a user ID from your public key ring: ! 694: ! 695: pgp -kr userid [keyring] ! 696: ! 697: This searches for the specified user ID in your key ring, and removes ! 698: it if it finds a match. Remember that any fragment of the user ID ! 699: will suffice for a match. The optional keyring file name is assumed ! 700: to be literally "pubring.pgp". It can be omitted, or you can specify ! 701: "secring.pgp" if you want to remove a secret key. You may specify a ! 702: different key ring file name. The default key ring extension is ! 703: ".pgp". ! 704: ! 705: If more than one user ID exists for this key, you will be asked if ! 706: you want to remove only the user ID you specified, while leaving the ! 707: key and its other user IDs intact. ! 708: ! 709: ! 710: ! 711: Extracting (copying) a Key from Your Key Ring ! 712: --------------------------------------------- ! 713: ! 714: To extract (copy) a key from your public or secret key ring: ! 715: ! 716: pgp -kx userid keyfile [keyring] ! 717: ! 718: This non-destructively copies the key specified by the user ID from ! 719: your public or secret key ring to the specified key file. This is ! 720: particularly useful if you want to give a copy of your public key to ! 721: someone else. ! 722: ! 723: If the key has any certifying signatures attached to it on your key ! 724: ring, they are copied off along with the key. ! 725: ! 726: If you want the extracted key represented in printable ASCII ! 727: characters suitable for email purposes, use the -kxa options. ! 728: ! 729: ! 730: ! 731: Viewing the Contents of Your Key Ring ! 732: ------------------------------------- ! 733: ! 734: To view the contents of your public key ring: ! 735: ! 736: pgp -kv[v] [userid] [keyring] ! 737: ! 738: This lists any keys in the key ring that match the specified user ID ! 739: substring. If you omit the user ID, all of the keys in the key ring ! 740: are listed. The optional keyring file name is assumed to be ! 741: "pubring.pgp". It can be omitted, or you can specify "secring.pgp" ! 742: if you want to list secret keys. If you want to specify a different ! 743: key ring file name, you can. The default key ring extension is ! 744: ".pgp". ! 745: ! 746: To see all the certifying signatures attached to each key, use the ! 747: -kvv option: ! 748: ! 749: pgp -kvv [userid] [keyring] ! 750: ! 751: If you want to specify a particular key ring file name, but want to ! 752: see all the keys in it, try this alternative approach: ! 753: ! 754: pgp keyfile ! 755: ! 756: With no command options specified, PGP lists all the keys in ! 757: keyfile.pgp, and also attempts to add them to your key ring if they ! 758: are not already on your key ring. ! 759: ! 760: ! 761: ! 762: How to Protect Public Keys from Tampering ! 763: ----------------------------------------- ! 764: ! 765: In a public key cryptosystem, you don't have to protect public keys ! 766: from exposure. In fact, it's better if they are widely disseminated. ! 767: But it is important to protect public keys from tampering, to make ! 768: sure that a public key really belongs to whom it appears to belong to. ! 769: This may be the most important vulnerability of a public-key ! 770: cryptosystem. Let's first look at a potential disaster, then at how ! 771: to safely avoid it with PGP. ! 772: ! 773: Suppose you wanted to send a private message to Alice. You download ! 774: Alice's public key certificate from an electronic bulletin board ! 775: system (BBS). You encrypt your letter to Alice with this public key ! 776: and send it to her through the BBS's E-mail facility. ! 777: ! 778: Unfortunately, unbeknownst to you or Alice, another user named ! 779: Charlie has infiltrated the BBS and generated a public key of his own ! 780: with Alice's user ID attached to it. He covertly substitutes his ! 781: bogus key in place of Alice's real public key. You unwittingly use ! 782: this bogus key belonging to Charlie instead of Alice's public key. ! 783: All looks normal because this bogus key has Alice's user ID. Now ! 784: Charlie can decipher the message intended for Alice because he has ! 785: the matching secret key. He may even re-encrypt the deciphered ! 786: message with Alice's real public key and send it on to her so that no ! 787: one suspects any wrongdoing. Furthermore, he can even make ! 788: apparently good signatures from Alice with this secret key because ! 789: everyone will use the bogus public key to check Alice's signatures. ! 790: ! 791: The only way to prevent this disaster is to prevent anyone from ! 792: tampering with public keys. If you got Alice's public key directly ! 793: from Alice, this is no problem. But that may be difficult if Alice ! 794: is a thousand miles away, or is currently unreachable. ! 795: ! 796: Perhaps you could get Alice's public key from a mutual trusted friend ! 797: David who knows he has a good copy of Alice's public key. David ! 798: could sign Alice's public key, vouching for the integrity of Alice's ! 799: public key. David would create this signature with his own secret ! 800: key. ! 801: ! 802: This would create a signed public key certificate, and would show ! 803: that Alice's key had not been tampered with. This requires you have a ! 804: known good copy of David's public key to check his signature. Perhaps ! 805: David could provide Alice with a signed copy of your public key also. ! 806: David is thus serving as an "introducer" between you and Alice. ! 807: ! 808: This signed public key certificate for Alice could be uploaded by ! 809: David or Alice to the BBS, and you could download it later. You ! 810: could then check the signature via David's public key and thus be ! 811: assured that this is really Alice's public key. No impostor can fool ! 812: you into accepting his own bogus key as Alice's because no one else ! 813: can forge signatures made by David. ! 814: ! 815: A widely trusted person could even specialize in providing this ! 816: service of "introducing" users to each other by providing signatures ! 817: for their public key certificates. This trusted person could be ! 818: regarded as a "key server", or as a "Certifying Authority". Any ! 819: public key certificates bearing the key server's signature could be ! 820: trusted as truly belonging to whom they appear to belong to. All ! 821: users who wanted to participate would need a known good copy of just ! 822: the key server's public key, so that the key server's signatures ! 823: could be verified. ! 824: ! 825: A trusted centralized key server or Certifying Authority is ! 826: especially appropriate for large impersonal centrally-controlled ! 827: corporate or government institutions. Some institutional ! 828: environments use hierarchies of Certifying Authorities. ! 829: ! 830: For more decentralized grassroots "guerrilla style" environments, ! 831: allowing all users to act as a trusted introducers for their friends ! 832: would probably work better than a centralized key server. PGP tends ! 833: to emphasize this organic decentralized non-institutional approach. ! 834: It better reflects the natural way humans interact on a personal ! 835: social level, and allows people to better choose who they can trust ! 836: for key management. ! 837: ! 838: This whole business of protecting public keys from tampering is the ! 839: single most difficult problem in practical public key applications. ! 840: It is the "Achilles heel" of public key cryptography, and a lot of ! 841: software complexity is tied up in solving this one problem. ! 842: ! 843: You should use a public key only after you are sure that it is a good ! 844: public key that has not been tampered with, and actually belongs to ! 845: the person it claims to. You can be sure of this if you got this ! 846: public key certificate directly from its owner, or if it bears the ! 847: signature of someone else that you trust, from whom you already have ! 848: a good public key. Also, the user ID should have the full name of ! 849: the key's owner, not just her first name. ! 850: ! 851: No matter how tempted you are-- and you will be tempted-- never, ! 852: NEVER give in to expediency and trust a public key you downloaded ! 853: from a bulletin board, unless it is signed by someone you trust. ! 854: That uncertified public key could have been tampered with by anyone, ! 855: maybe even by the system administrator of the bulletin board. ! 856: ! 857: If you are asked to sign someone else's public key certificate, make ! 858: certain that it really belongs to that person named in the user ID of ! 859: that public key certificate. This is because your signature on her ! 860: public key certificate is a promise by you that this public key ! 861: really belongs to her. Other people who trust you will accept her ! 862: public key because it bears your signature. It may be ill-advised to ! 863: rely on hearsay-- don't sign her public key unless you have ! 864: independent firsthand knowledge that it really belongs to her. ! 865: Preferably, you should sign it only if you got it directly from her. ! 866: ! 867: In order to sign a public key, you must be far more certain of that ! 868: key's ownership than if you merely want to use that key to encrypt a ! 869: message. To be convinced of a key's validity enough to use it, ! 870: certifying signatures from trusted introducers should suffice. But ! 871: to sign a key yourself, you should require your own independent ! 872: firsthand knowledge of who owns that key. Perhaps you could call the ! 873: key's owner on the phone and read the key file to her to get her to ! 874: confirm that the key you have really is her key-- and make sure you ! 875: really are talking to the right person. See the section called ! 876: "Verifying a Public Key Over the Phone" in the Special Topics volume ! 877: for further details. ! 878: ! 879: Bear in mind that your signature on a public key certificate does not ! 880: vouch for the integrity of that person, but only vouches for the ! 881: integrity (the ownership) of that person's public key. You aren't ! 882: risking your credibility by signing the public key of a sociopath, if ! 883: you were completely confident that the key really belonged to him. ! 884: Other people would accept that key as belonging to him because you ! 885: signed it (assuming they trust you), but they wouldn't trust that ! 886: key's owner. Trusting a key is not the same as trusting the key's ! 887: owner. ! 888: ! 889: Trust is not necessarily transferable; I have a friend who I trust ! 890: not to lie. He's a gullible person who trusts the President not to ! 891: lie. That doesn't mean I trust the President not to lie. This is ! 892: just common sense. If I trust Alice's signature on a key, and Alice ! 893: trusts Charlie's signature on a key, that does not imply that I have ! 894: to trust Charlie's signature on a key. ! 895: ! 896: It would be a good idea to keep your own public key on hand with a ! 897: collection of certifying signatures attached from a variety of ! 898: "introducers", in the hopes that most people will trust at least one ! 899: of the introducers who vouch for your own public key's validity. ! 900: You could post your key with its attached collection of certifying ! 901: signatures on various electronic bulletin boards. If you sign ! 902: someone else's public key, return it to them with your signature so ! 903: that they can add it to their own collection of credentials for their ! 904: own public key. ! 905: ! 906: PGP keeps track of which keys on your public key ring are properly ! 907: certified with signatures from introducers that you trust. All you ! 908: have to do is tell PGP which people you trust as introducers, and ! 909: certify their keys yourself with your own ultimately trusted key. ! 910: PGP can take it from there, automatically validating any other keys ! 911: that have been signed by your designated introducers. And of course ! 912: you may directly sign more keys yourself. More on this later. ! 913: ! 914: Make sure no one else can tamper with your own public key ring. ! 915: Checking a new signed public key certificate must ultimately depend ! 916: on the integrity of the trusted public keys that are already on your ! 917: own public key ring. Maintain physical control of your public key ! 918: ring, preferably on your own personal computer rather than on a ! 919: remote timesharing system, just as you would do for your secret key. ! 920: This is to protect it from tampering, not from disclosure. Keep a ! 921: trusted backup copy of your public key ring and your secret key ring ! 922: on write-protected media. ! 923: ! 924: Since your own trusted public key is used as a final authority to ! 925: directly or indirectly certify all the other keys on your key ring, ! 926: it is the most important key to protect from tampering. To detect ! 927: any tampering of your own ultimately-trusted public key, PGP can be ! 928: set up to automatically compare your public key against a backup copy ! 929: on write-protected media. For details, see the description of the ! 930: "-kc" key ring check command in the Special Topics volume. ! 931: ! 932: PGP generally assumes you will maintain physical security over your ! 933: system and your key rings, as well as your copy of PGP itself. If an ! 934: intruder can tamper with your disk, then in theory he can tamper with ! 935: PGP itself, rendering moot the safeguards PGP may have to detect ! 936: tampering with keys. ! 937: ! 938: One somewhat complicated way to protect your own whole public key ring ! 939: from tampering is to sign the whole ring with your own secret key. ! 940: You could do this by making a detached signature certificate of the ! 941: public key ring, by signing the ring with the "-sb" options (see the ! 942: section called "Separating Signatures from Messages" in the PGP ! 943: User's Guide, Special Topics volume). Unfortunately, you would still ! 944: have to keep a separate trusted copy of your own public key around to ! 945: check the signature you made. You couldn't rely on your own public ! 946: key stored on your public key ring to check the signature you made ! 947: for the whole ring, because that is part of what you're trying to ! 948: check. ! 949: ! 950: ! 951: ! 952: How Does PGP Keep Track of Which Keys are Valid? ! 953: ------------------------------------------------ ! 954: ! 955: Before you read this section, be sure to read the above section on ! 956: "How to Protect Public Keys from Tampering". ! 957: ! 958: PGP keeps track of which keys on your public key ring are properly ! 959: certified with signatures from introducers that you trust. All you ! 960: have to do is tell PGP which people you trust as introducers, and ! 961: certify their keys yourself with your own ultimately trusted key. ! 962: PGP can take it from there, automatically validating any other keys ! 963: that have been signed by your designated introducers. And of course ! 964: you may directly sign more keys yourself. ! 965: ! 966: There are two entirely separate criteria PGP uses to judge a public ! 967: key's usefulness-- don't get them confused: ! 968: ! 969: 1) Does the key actually belong to whom it appears to belong? ! 970: In other words, has it been certified with a trusted signature? ! 971: 2) Does it belong to someone you can trust to certify other keys? ! 972: ! 973: PGP can calculate the answer to the first question. To answer the ! 974: second question, PGP must be explicitly told by you, the user. When ! 975: you supply the answer to question 2, PGP can then calculate the ! 976: answer to question 1 for other keys signed by the introducer you ! 977: designated as trusted. ! 978: ! 979: Keys that have been certified by a trusted introducer are deemed ! 980: valid by PGP. The keys belonging to trusted introducers must ! 981: themselves be certified either by you or by other trusted ! 982: introducers. ! 983: ! 984: PGP also allows for the possibility of you having several shades of ! 985: trust for people to act as introducers. Your trust for a key's owner ! 986: to act as an introducer does not just reflect your estimation of ! 987: their personal integrity-- it should also reflect how competent you ! 988: think they are at understanding key management and using good ! 989: judgment in signing keys. You can designate a person to PGP as ! 990: unknown, untrusted, marginally trusted, or completely trusted to ! 991: certify other public keys. This trust information is stored on your ! 992: key ring with their key, but when you tell PGP to copy a key off your ! 993: key ring, PGP will not copy the trust information along with the key, ! 994: because your private opinions on trust are regarded as confidential. ! 995: ! 996: When PGP is calculating the validity of a public key, it examines the ! 997: trust level of all the attached certifying signatures. It computes a ! 998: weighted score of validity-- two marginally trusted signatures are ! 999: deemed as credible as one fully trusted signature. PGP's skepticism ! 1000: is adjustable-- for example, you may tune PGP to require two fully ! 1001: trusted signatures or three marginally trusted signatures to judge a ! 1002: key as valid. ! 1003: ! 1004: Your own key is "axiomatically" valid to PGP, needing no introducer's ! 1005: signature to prove its validity. PGP knows which public keys are ! 1006: yours, by looking for the corresponding secret keys on the secret ! 1007: key ring. PGP also assumes you ultimately trust yourself to certify ! 1008: other keys. ! 1009: ! 1010: As time goes on, you will accumulate keys from other people that you ! 1011: may want to designate as trusted introducers. Everyone else will ! 1012: each choose their own trusted introducers. And everyone will ! 1013: gradually accumulate and distribute with their key a collection of ! 1014: certifying signatures from other people, with the expectation that ! 1015: anyone receiving it will trust at least one or two of the signatures. ! 1016: This will cause the emergence of a decentralized fault-tolerant web ! 1017: of confidence for all public keys. ! 1018: ! 1019: This unique grass-roots approach contrasts sharply with Government ! 1020: standard public key management schemes, such as Internet Privacy ! 1021: Enhanced Mail (PEM), which are based on centralized control and ! 1022: mandatory centralized trust. The standard schemes rely on a ! 1023: hierarchy of Certifying Authorities who dictate who you must trust. ! 1024: PGP's decentralized probabilistic method for determining public key ! 1025: legitimacy is the centerpiece of its key management architecture. ! 1026: PGP lets you alone choose who you trust, putting you at the top of ! 1027: your own private certification pyramid. PGP is for people who prefer ! 1028: to pack their own parachutes. ! 1029: ! 1030: ! 1031: ! 1032: How to Protect Secret Keys from Disclosure ! 1033: ------------------------------------------ ! 1034: ! 1035: Protect your own secret key and your pass phrase carefully. Really, ! 1036: really carefully. If your secret key is ever compromised, you'd ! 1037: better get the word out quickly to all interested parties (good luck) ! 1038: before someone else uses it to make signatures in your name. For ! 1039: example, they could use it to sign bogus public key certificates, ! 1040: which could create problems for many people, especially if your ! 1041: signature is widely trusted. And of course, a compromise of your own ! 1042: secret key could expose all messages sent to you. ! 1043: ! 1044: To protect your secret key, you can start by always keeping physical ! 1045: control of your secret key. Keeping it on your personal computer at ! 1046: home is OK, or keep it in your notebook computer that you can carry ! 1047: with you. If you must use an office computer that you don't always ! 1048: have physical control of, then keep your public and secret key rings ! 1049: on a write-protected removable floppy disk, and don't leave it behind ! 1050: when you leave the office. It wouldn't be a good idea to allow your ! 1051: secret key to reside on a remote timesharing computer, such as a ! 1052: remote dial-in Unix system. Someone could eavesdrop on your modem ! 1053: line and capture your pass phrase, and then obtain your actual secret ! 1054: key from the remote system. You should only use your secret key on a ! 1055: machine that you have physical control over. ! 1056: ! 1057: Don't store your pass phrase anywhere on the computer that has your ! 1058: secret key file. Storing both the secret key and the pass phrase on ! 1059: the same computer is as dangerous as keeping your PIN in the same ! 1060: wallet as your Automatic Teller Machine bank card. You don't want ! 1061: somebody to get their hands on your disk containing both the pass ! 1062: phrase and the secret key file. It would be most secure if you just ! 1063: memorize your pass phrase and don't store it anywhere but your brain. ! 1064: If you feel you must write down your pass phrase, keep it well ! 1065: protected, perhaps even more well protected than the secret key file. ! 1066: ! 1067: And keep backup copies of your secret key ring-- remember, you have ! 1068: the only copy of your secret key, and losing it will render useless ! 1069: all the copies of your public key that you have spread throughout the ! 1070: world. ! 1071: ! 1072: The decentralized non-institutional approach PGP uses to manage ! 1073: public keys has its benefits, but unfortunately this also means we ! 1074: can't rely on a single centralized list of which keys have been ! 1075: compromised. This makes it a bit harder to contain the damage of a ! 1076: secret key compromise. You just have to spread the word and hope ! 1077: everyone hears about it. ! 1078: ! 1079: If the worst case happens-- your secret key and pass phrase are both ! 1080: compromised (hopefully you will find this out somehow)-- you will ! 1081: have to issue a "key compromise" certificate. This kind of ! 1082: certificate is used to warn other people to stop using your public ! 1083: key. You can use PGP to create such a certificate by using the "-kd" ! 1084: command. Then you must somehow send this compromise certificate to ! 1085: everyone else on the planet, or at least to all your friends and ! 1086: their friends, et cetera. Their own PGP software will install this ! 1087: key compromise certificate on their public key rings and will ! 1088: automatically prevent them from accidentally using your public key ! 1089: ever again. You can then generate a new secret/public key pair and ! 1090: publish the new public key. You could send out one package containing ! 1091: both your new public key and the key compromise certificate for your ! 1092: old key. ! 1093: ! 1094: ! 1095: ! 1096: Revoking a Public Key ! 1097: --------------------- ! 1098: ! 1099: Suppose your secret key and your pass phrase are somehow both ! 1100: compromised. You have to get the word out to the rest of the world, ! 1101: so that they will all stop using your public key. To do this, you ! 1102: will have to issue a "key compromise", or "key revocation" certificate ! 1103: to revoke your public key. ! 1104: ! 1105: To generate a certificate to revoke your own key, use the -kd ! 1106: command: ! 1107: ! 1108: pgp -kd your_userid ! 1109: ! 1110: This certificate bears your signature, made with the same key you are ! 1111: revoking. You should widely disseminate this key revocation ! 1112: certificate as soon as possible. Other people who receive it can add ! 1113: it to their public key rings, and their PGP software then ! 1114: automatically prevents them from accidentally using your old public ! 1115: key ever again. You can then generate a new secret/public key pair ! 1116: and publish the new public key. ! 1117: ! 1118: You may choose to revoke your key for some other reason than the ! 1119: compromise of a secret key. If so, you may still use the same ! 1120: mechanism to revoke it. ! 1121: ! 1122: ! 1123: ! 1124: What If You Lose Your Secret Key? ! 1125: --------------------------------- ! 1126: ! 1127: Normally, if you want to revoke your own secret key, you can use the ! 1128: "-kd" command to issue a revocation certificate, signed with your own ! 1129: secret key (see "Revoking a Public Key"). ! 1130: ! 1131: But what can you do if you lose your secret key, or if your secret ! 1132: key is destroyed? You can't revoke it yourself, because you must use ! 1133: your own secret key to revoke it, and you don't have it anymore. A ! 1134: future version of PGP will offer a more secure means of revoking keys ! 1135: in these circumstances, allowing trusted introducers to certify that ! 1136: a public key has been revoked. But for now, you will have to get the ! 1137: word out through whatever informal means you can, asking users to ! 1138: "disable" your public key on their own individual public key rings. ! 1139: ! 1140: Other users may disable your public key on their own public key rings ! 1141: by using the "-kd" command. If a user ID is specified that does not ! 1142: correspond to a secret key on the secret key ring, the -kd command ! 1143: will look for that user ID on the public key ring, and mark that ! 1144: public key as disabled. A disabled key may not be used to encrypt ! 1145: any messages, and may not be extracted from the key ring with the -kx ! 1146: command. It can still be used to check signatures, but a warning is ! 1147: displayed. And if the user tries to add the same key again to his ! 1148: key ring, it will not work because the disabled key is already on the ! 1149: key ring. These combined features will help curtail the further ! 1150: spread of a disabled key. ! 1151: ! 1152: If the specified public key is already disabled, the -kd command will ! 1153: ask if you want the key reenabled. ! 1154: ! 1155: ! 1156: Advanced Topics ! 1157: =============== ! 1158: ! 1159: Most of the "Advanced Topics" are covered in the "PGP User's Guide, ! 1160: Volume II: Special Topics". But here are a few topics that bear ! 1161: mentioning here. ! 1162: ! 1163: ! 1164: Sending Ciphertext Through E-mail Channels: Radix-64 Format ! 1165: ----------------------------------------------------------- ! 1166: ! 1167: Many electronic mail systems only allow messages made of ASCII text, ! 1168: not the 8-bit raw binary data that ciphertext is made of. To get ! 1169: around this problem, PGP supports ASCII radix-64 format for ! 1170: ciphertext messages, similar to the Internet Privacy-Enhanced Mail ! 1171: (PEM) format. This special format represents binary data by using ! 1172: only printable ASCII characters, so it is useful for transmitting ! 1173: binary encrypted data through 7-bit channels or for sending binary ! 1174: encrypted data as normal E-mail text. This format acts as a form of ! 1175: "transport armor", protecting it against corruption as it travels ! 1176: through intersystem gateways on Internet. It also appends a CRC to ! 1177: detect transmission errors. ! 1178: ! 1179: Radix-64 format converts the plaintext by expanding groups of 3 ! 1180: binary 8-bit bytes into 4 printable ASCII characters, so the file ! 1181: grows by about 33%. But this expansion isn't so bad when you ! 1182: consider that the file probably was compressed more than that by PGP ! 1183: before it was encrypted. ! 1184: ! 1185: To produce a ciphertext file in ASCII radix-64 format, just add the ! 1186: "a" option when encrypting or signing a message, like so: ! 1187: ! 1188: pgp -esa message.txt her_userid ! 1189: ! 1190: This example produces a ciphertext file called "message.asc" that ! 1191: contains data in a PEM-like ASCII radix-64 format. This file can be ! 1192: easily uploaded into a text editor through 7-bit channels for ! 1193: transmission as normal E-mail on Internet or any other E-mail ! 1194: network. ! 1195: ! 1196: Decrypting the radix-64 transport-armored message is no different than ! 1197: a normal decrypt. For example: ! 1198: ! 1199: pgp message ! 1200: ! 1201: PGP automatically looks for the ASCII file "message.asc" before it ! 1202: looks for the binary file "message.pgp". It recognizes that the file ! 1203: is in radix-64 format and converts it back to binary before ! 1204: processing as it normally does, producing as a by-product a ".pgp" ! 1205: ciphertext file in binary form. The final output file is in normal ! 1206: plaintext form, just as it was in the original file "message.txt". ! 1207: ! 1208: Most Internet E-mail facilities prohibit sending messages that are ! 1209: more than 50000 bytes long. Longer messages must be broken into ! 1210: smaller chunks that can be mailed separately. If your encrypted ! 1211: message is very large, and you requested radix-64 format, PGP ! 1212: automatically breaks it up into chunks that are each small enough to ! 1213: send via E-mail. The chunks are put into files named with extensions ! 1214: ".as1", ".as2", ".as3", etc. The recipient must concatenate these ! 1215: separate files back together in their proper order into one big file ! 1216: before decrypting it. While decrypting, PGP ignores any extraneous ! 1217: text in mail headers that are not enclosed in the radix-64 message ! 1218: blocks. ! 1219: ! 1220: If you want to send a public key to someone else in radix-64 format, ! 1221: just add the -a option while extracting the key from your keyring. ! 1222: ! 1223: If you forgot to use the -a option when you made a ciphertext file or ! 1224: extracted a key, you may still directly convert the binary file into ! 1225: radix-64 format by simply using the -a option alone, without any ! 1226: encryption specified. PGP converts it to a ".asc" file. ! 1227: ! 1228: If you want to send through an E-mail channel a plaintext file that ! 1229: is signed but not encrypted, PGP will normally convert it all into ! 1230: radix-64 armor, rendering it unreadable to the casual human observer. ! 1231: If the original plaintext message is in text (not binary) form, there ! 1232: is a way to send it through an E-mail channel in such a way that the ! 1233: ASCII armor is applied only to the binary signature certificate, but ! 1234: not to the plaintext message. This makes it possible for the ! 1235: recipient to read the signed message with human eyes, without the aid ! 1236: of PGP. Of course, PGP is still needed to actually check the ! 1237: signature. For further information on this feature, see the ! 1238: explanation of the CLEARSIG parameter in the section "Setting ! 1239: Configuration Parameters: CONFIG.TXT" in the Special Topics volume. ! 1240: ! 1241: ! 1242: Environmental Variable for Path Name ! 1243: ------------------------------------ ! 1244: ! 1245: PGP uses several special files for its purposes, such as your ! 1246: standard key ring files "pubring.pgp" and "secring.pgp", the random ! 1247: number seed file "randseed.bin", the PGP configuration file ! 1248: "config.txt", and the foreign language string translation file ! 1249: "language.txt". These special files can be kept in any directory, by ! 1250: setting the environmental variable "PGPPATH" to the desired pathname. ! 1251: For example, on MSDOS, the shell command: ! 1252: ! 1253: SET PGPPATH=C:\PGP ! 1254: ! 1255: makes PGP assume that your public key ring filename is ! 1256: "C:\PGP\pubring.pgp". Assuming, of course, that this directory ! 1257: exists. Use your favorite text editor to modify your MSDOS ! 1258: AUTOEXEC.BAT file to automatically set up this variable whenever you ! 1259: start up your system. If PGPPATH remains undefined, these special ! 1260: files are assumed to be in the current directory. ! 1261: ! 1262: ! 1263: ! 1264: Setting Configuration Parameters: CONFIG.TXT ! 1265: -------------------------------------------- ! 1266: ! 1267: PGP has a number of user-settable parameters that can be defined in a ! 1268: special configuration text file called "config.txt", in the directory ! 1269: pointed to by the shell environmental variable PGPPATH. Having a ! 1270: configuration file enables the user to define various flags and ! 1271: parameters for PGP without the burden of having to always define ! 1272: these parameters in the PGP command line. ! 1273: ! 1274: With these configuration parameters, for example, you can control ! 1275: where PGP stores its temporary scratch files, or you can select what ! 1276: foreign language PGP will use to display its diagnostics messages and ! 1277: user prompts, or you can adjust PGP's level of skepticism in ! 1278: determining a key's validity based on the number of certifying ! 1279: signatures it has. ! 1280: ! 1281: For more details on setting these configuration parameters, see the ! 1282: appropriate section of the PGP User's Guide, Special Topics volume. ! 1283: ! 1284: ! 1285: ! 1286: Vulnerabilities ! 1287: --------------- ! 1288: ! 1289: No data security system is impenetrable. PGP can be circumvented in ! 1290: a variety of ways. Potential vulnerabilities you should be aware of ! 1291: include compromising your pass phrase or secret key, public key ! 1292: tampering, files that you deleted but are still somewhere on the ! 1293: disk, viruses and Trojan horses, breaches in your physical security, ! 1294: electromagnetic emissions, exposure on multi-user systems, traffic ! 1295: analysis, and perhaps even direct cryptanalysis. ! 1296: ! 1297: For a detailed discussion of these issues, see the "Vulnerabilities" ! 1298: section in the PGP User's Guide, Special Topics volume. ! 1299: ! 1300: ! 1301: Beware of Snake Oil ! 1302: =================== ! 1303: ! 1304: When examining a cryptographic software package, the question always ! 1305: remains, why should you trust this product? Even if you examined the ! 1306: source code yourself, not everyone has the cryptographic experience ! 1307: to judge the security. Even if you are an experienced cryptographer, ! 1308: subtle weaknesses in the algorithms could still elude you. ! 1309: ! 1310: When I was in college in the early seventies, I devised what I ! 1311: believed was a brilliant encryption scheme. A simple pseudorandom ! 1312: number stream was added to the plaintext stream to create ! 1313: ciphertext. This would seemingly thwart any frequency analysis of ! 1314: the ciphertext, and would be uncrackable even to the most resourceful ! 1315: Government intelligence agencies. I felt so smug about my ! 1316: achievement. So cock-sure. ! 1317: ! 1318: Years later, I discovered this same scheme in several introductory ! 1319: cryptography texts and tutorial papers. How nice. Other ! 1320: cryptographers had thought of the same scheme. Unfortunately, the ! 1321: scheme was presented as a simple homework assignment on how to use ! 1322: elementary cryptanalytic techniques to trivially crack it. So much ! 1323: for my brilliant scheme. ! 1324: ! 1325: From this humbling experience I learned how easy it is to fall into a ! 1326: false sense of security when devising an encryption algorithm. Most ! 1327: people don't realize how fiendishly difficult it is to devise an ! 1328: encryption algorithm that can withstand a prolonged and determined ! 1329: attack by a resourceful opponent. Many mainstream software engineers ! 1330: have developed equally naive encryption schemes (often even the very ! 1331: same encryption scheme), and some of them have been incorporated into ! 1332: commercial encryption software packages and sold for good money to ! 1333: thousands of unsuspecting users. ! 1334: ! 1335: This is like selling automotive seat belts that look good and feel ! 1336: good, but snap open in even the slowest crash test. Depending on ! 1337: them may be worse than not wearing seat belts at all. No one ! 1338: suspects they are bad until a real crash. Depending on weak ! 1339: cryptographic software may cause you to unknowingly place sensitive ! 1340: information at risk. You might not otherwise have done so if you had ! 1341: no cryptographic software at all. Perhaps you may never even ! 1342: discover your data has been compromised. ! 1343: ! 1344: Sometimes commercial packages use the Federal Data Encryption ! 1345: Standard (DES), a good conventional algorithm recommended by the ! 1346: Government for commercial use (but not for classified information, ! 1347: oddly enough-- hmmm). There are several "modes of operation" the ! 1348: DES can use, some of them better than others. The Government ! 1349: specifically recommends not using the weakest simplest mode for ! 1350: messages, the Electronic Codebook (ECB) mode. But they do recommend ! 1351: the stronger and more complex Cipher Feedback (CFB) or Cipher Block ! 1352: Chaining (CBC) modes. ! 1353: ! 1354: Unfortunately, most of the commercial encryption packages I've looked ! 1355: at use ECB mode. When I've talked to the authors of a number of ! 1356: these implementations, they say they've never heard of CBC or CFB ! 1357: modes, and didn't know anything about the weaknesses of ECB mode. ! 1358: The very fact that they haven't even learned enough cryptography to ! 1359: know these elementary concepts is not reassuring. These same ! 1360: software packages often include a second faster encryption algorithm ! 1361: that can be used instead of the slower DES. The author of the ! 1362: package often thinks his proprietary faster algorithm is as secure as ! 1363: the DES, but after questioning him I usually discover that it's just ! 1364: a variation of my own brilliant scheme from college days. Or maybe ! 1365: he won't even reveal how his proprietary encryption scheme works, but ! 1366: assures me it's a brilliant scheme and I should trust it. I'm sure ! 1367: he believes that his algorithm is brilliant, but how can I know that ! 1368: without seeing it? ! 1369: ! 1370: In all fairness I must point out that in most cases these products do ! 1371: not come from companies that specialize in cryptographic technology. ! 1372: ! 1373: There is a company called AccessData (87 East 600 South, Orem, Utah ! 1374: 84058, phone 1-800-658-5199) that sells a package for $185 that ! 1375: cracks the built-in encryption schemes used by WordPerfect, Lotus ! 1376: 1-2-3, MS Excel, Symphony, Quattro Pro, Paradox, and MS Word 2.0. It ! 1377: doesn't simply guess passwords-- it does real cryptanalysis. Some ! 1378: people buy it when they forget their password for their own files. ! 1379: Law enforcement agencies buy it too, so they can read files they ! 1380: seize. I talked to Eric Thompson, the author, and he said his ! 1381: program only takes a split second to crack them, but he put in some ! 1382: delay loops to slow it down so it doesn't look so easy to the ! 1383: customer. He also told me that the password encryption feature of ! 1384: PKZIP files can often be easily broken, and that his law enforcement ! 1385: customers already have that service regularly provided to them from ! 1386: another vendor. ! 1387: ! 1388: In some ways, cryptography is like pharmaceuticals. Its integrity ! 1389: may be absolutely crucial. Bad penicillin looks the same as good ! 1390: penicillin. You can tell if your spreadsheet software is wrong, but ! 1391: how do you tell if your cryptography package is weak? The ciphertext ! 1392: produced by a weak encryption algorithm looks as good as ciphertext ! 1393: produced by a strong encryption algorithm. There's a lot of snake ! 1394: oil out there. A lot of quack cures. Unlike the patent medicine ! 1395: hucksters of old, these software implementors usually don't even know ! 1396: their stuff is snake oil. They may be good software engineers, but ! 1397: they usually haven't even read any of the academic literature in ! 1398: cryptography. But they think they can write good cryptographic ! 1399: software. And why not? After all, it seems intuitively easy to do ! 1400: so. And their software seems to work okay. ! 1401: ! 1402: Anyone who thinks they have devised an unbreakable encryption scheme ! 1403: either is an incredibly rare genius or is naive and inexperienced. ! 1404: ! 1405: I remember a conversation with Brian Snow, a highly placed senior ! 1406: cryptographer with the NSA. He said he would never trust an ! 1407: encryption algorithm designed by someone who had not "earned their ! 1408: bones" by first spending a lot of time cracking codes. That did make ! 1409: a lot of sense. I observed that practically no one in the commercial ! 1410: world of cryptography qualified under this criterion. "Yes", he said ! 1411: with a self assured smile, "And that makes our job at NSA so much ! 1412: easier." A chilling thought. I didn't qualify either. ! 1413: ! 1414: The Government has peddled snake oil too. After World War II, the US ! 1415: sold German Enigma ciphering machines to third world governments. ! 1416: But they didn't tell them that the Allies cracked the Enigma code ! 1417: during the war, a fact that remained classified for many years. Even ! 1418: today many Unix systems worldwide use the Enigma cipher for file ! 1419: encryption, in part because the Government has created legal ! 1420: obstacles against using better algorithms. They even tried to ! 1421: prevent the initial publication of the RSA algorithm in 1977. And ! 1422: they have squashed essentially all commercial efforts to develop ! 1423: effective secure telephones for the general public. ! 1424: ! 1425: The principle job of the US Government's National Security Agency is ! 1426: to gather intelligence, principally by covertly tapping into people's ! 1427: private communications (see James Bamford's book, "The Puzzle ! 1428: Palace"). The NSA has amassed considerable skill and resources for ! 1429: cracking codes. When people can't get good cryptography to protect ! 1430: themselves, it makes NSA's job much easier. NSA also has the ! 1431: responsibility of approving and recommending encryption algorithms. ! 1432: Some critics charge that this is a conflict of interest, like putting ! 1433: the fox in charge of guarding the hen house. NSA has been pushing a ! 1434: conventional encryption algorithm that they designed, and they won't ! 1435: tell anybody how it works because that's classified. They want ! 1436: others to trust it and use it. But any cryptographer can tell you ! 1437: that a well-designed encryption algorithm does not have to be ! 1438: classified to remain secure. Only the keys should need protection. ! 1439: How does anyone else really know if NSA's classified algorithm is ! 1440: secure? It's not that hard for NSA to design an encryption algorithm ! 1441: that only they can crack, if no one else can review the algorithm. ! 1442: Are they deliberately selling snake oil? ! 1443: ! 1444: I'm not as certain about the security of PGP as I once was about my ! 1445: brilliant encryption software from college. If I were, that would be ! 1446: a bad sign. But I'm pretty sure that PGP does not contain any ! 1447: glaring weaknesses. The crypto algorithms were developed by people ! 1448: at high levels of civilian cryptographic academia, and have been ! 1449: individually subject to extensive peer review. Source code is ! 1450: available to facilitate peer review of PGP and to help dispel the ! 1451: fears of some users. It's reasonably well researched, and has been ! 1452: years in the making. And I don't work for the NSA. I hope it ! 1453: doesn't require too large a "leap of faith" to trust the security of ! 1454: PGP. ! 1455: ! 1456: ! 1457: PGP Quick Reference ! 1458: =================== ! 1459: ! 1460: Here's a quick summary of PGP commands. ! 1461: ! 1462: ! 1463: To encrypt a plaintext file with the recipient's public key: ! 1464: pgp -e textfile her_userid ! 1465: ! 1466: To sign a plaintext file with your secret key: ! 1467: pgp -s textfile [-u your_userid] ! 1468: ! 1469: To sign a plaintext file with your secret key, and then encrypt it ! 1470: with the recipient's public key: ! 1471: pgp -es textfile her_userid [-u your_userid] ! 1472: ! 1473: To encrypt a plaintext file with just conventional cryptography, type: ! 1474: pgp -c textfile ! 1475: ! 1476: To decrypt an encrypted file, or to check the signature integrity of a ! 1477: signed file: ! 1478: pgp ciphertextfile [-o plaintextfile] ! 1479: ! 1480: To encrypt a message for any number of multiple recipients: ! 1481: pgp -e textfile userid1 userid2 userid3 ! 1482: ! 1483: --- Key management commands: ! 1484: ! 1485: To generate your own unique public/secret key pair: ! 1486: pgp -kg ! 1487: ! 1488: To add a public or secret key file's contents to your public or ! 1489: secret key ring: ! 1490: pgp -ka keyfile [keyring] ! 1491: ! 1492: To extract (copy) a key from your public or secret key ring: ! 1493: pgp -kx userid keyfile [keyring] ! 1494: or: pgp -kxa userid keyfile [keyring] ! 1495: ! 1496: To view the contents of your public key ring: ! 1497: pgp -kv[v] [userid] [keyring] ! 1498: ! 1499: To view the "fingerprint" of a public key, to help verify it over ! 1500: the telephone with its owner: ! 1501: pgp -kvc [userid] [keyring] ! 1502: ! 1503: To view the contents and check the certifying signatures of your ! 1504: public key ring: ! 1505: pgp -kc [userid] [keyring] ! 1506: ! 1507: To edit the userid or pass phrase for your secret key: ! 1508: pgp -ke userid [keyring] ! 1509: ! 1510: To edit the trust parameters for a public key: ! 1511: pgp -ke userid [keyring] ! 1512: ! 1513: To remove a key or just a userid from your public key ring: ! 1514: pgp -kr userid [keyring] ! 1515: ! 1516: To sign and certify someone else's public key on your public key ring: ! 1517: pgp -ks her_userid [-u your_userid] [keyring] ! 1518: ! 1519: To remove selected signatures from a userid on a keyring: ! 1520: pgp -krs userid [keyring] ! 1521: ! 1522: To permanently revoke your own key, issuing a key compromise ! 1523: certificate: ! 1524: pgp -kd your_userid ! 1525: ! 1526: To disable or reenable a public key on your own public key ring: ! 1527: pgp -kd userid ! 1528: ! 1529: --- Esoteric commands: ! 1530: ! 1531: To decrypt a message and leave the signature on it intact: ! 1532: pgp -d ciphertextfile ! 1533: ! 1534: To create a signature certificate that is detached from the document: ! 1535: pgp -sb textfile [-u your_userid] ! 1536: ! 1537: To detach a signature certificate from a signed message: ! 1538: pgp -b ciphertextfile ! 1539: ! 1540: --- Command options that can be used in combination with other ! 1541: command options (sometimes even spelling interesting words!): ! 1542: ! 1543: To produce a ciphertext file in ASCII radix-64 format, just add the ! 1544: -a option when encrypting or signing a message or extracting a key: ! 1545: pgp -sea textfile her_userid ! 1546: or: pgp -kxa userid keyfile [keyring] ! 1547: ! 1548: To wipe out the plaintext file after producing the ciphertext file, ! 1549: just add the -w (wipe) option when encrypting or signing a message: ! 1550: pgp -sew message.txt her_userid ! 1551: ! 1552: To specify that a plaintext file contains ASCII text, not binary, and ! 1553: should be converted to recipient's local text line conventions, add ! 1554: the -t (text) option to other options: ! 1555: pgp -seat message.txt her_userid ! 1556: ! 1557: To view the decrypted plaintext output on your screen (like the ! 1558: Unix-style "more" command), without writing it to a file, use ! 1559: the -m (more) option while decrypting: ! 1560: pgp -m ciphertextfile ! 1561: ! 1562: To specify that the recipient's decrypted plaintext will be shown ! 1563: ONLY on her screen and cannot be saved to disk, add the -m option: ! 1564: pgp -steam message.txt her_userid ! 1565: ! 1566: To recover the original plaintext filename while decrypting, add ! 1567: the -p option: ! 1568: pgp -p ciphertextfile ! 1569: ! 1570: To use a Unix-style filter mode, reading from standard input and ! 1571: writing to standard output, add the -f option: ! 1572: pgp -feast her_userid <inputfile >outputfile ! 1573: ! 1574: ! 1575: ! 1576: Legal Issues ! 1577: ============ ! 1578: ! 1579: For detailed information on PGP(tm) licensing, distribution, ! 1580: copyrights, patents, trademarks, liability limitations, and export ! 1581: controls, see the "Legal Issues" section in the "PGP User's Guide, ! 1582: Volume II: Special Topics". ! 1583: ! 1584: PGP uses a public key algorithm claimed by U.S. patent #4,405,829. ! 1585: The exclusive licensing rights to this patent are held by a ! 1586: California company called Public Key Partners, and you may be ! 1587: infringing the patent if you use PGP in the USA without a license. ! 1588: These issues are detailed in the Volume II manual, and in the RSAREF ! 1589: 2.0 license, dated 16 March 1994. PKP has licensed others to ! 1590: practice the patent, including a company known as ViaCrypt, in ! 1591: Phoenix, Arizona. ViaCrypt sells a fully licensed version of PGP. ! 1592: ViaCrypt may be reached at 602-944-0773. ! 1593: ! 1594: PGP is "guerrilla" freeware, and I don't mind if you distribute it ! 1595: widely. Just don't ask me to send you a copy. Instead, you can look ! 1596: for it yourself on many BBS systems and a number of Internet FTP ! 1597: sites. But before you distribute PGP, it is essential that you ! 1598: understand the U.S. export controls on encryption software. ! 1599: ! 1600: ! 1601: ! 1602: Acknowledgments ! 1603: ================ ! 1604: ! 1605: I'd like to thank the following people for their contributions to the ! 1606: creation of Pretty Good Privacy. Although I was the author of PGP ! 1607: version 1.0, major parts of later versions of PGP were implemented by ! 1608: an international collaborative effort involving a large number of ! 1609: contributors, under my design guidance. ! 1610: ! 1611: Branko Lankester, Hal Finney and Peter Gutmann all contributed a huge ! 1612: amount of time in adding features for PGP 2.0, and ported it to Unix ! 1613: variants. ! 1614: ! 1615: Hugh Kennedy ported it to VAX/VMS, Lutz Frank ported it to the Atari ! 1616: ST, and Cor Bosman and Colin Plumb ported it to the Commodore Amiga. ! 1617: ! 1618: Translation of PGP into foreign languages was done by Jean-loup ! 1619: Gailly in France, Armando Ramos in Spain, Felipe Rodriquez Svensson ! 1620: and Branko Lankester in The Netherlands, Miguel Angel Gallardo in ! 1621: Spain, Hugh Kennedy and Lutz Frank in Germany, David Vincenzetti in ! 1622: Italy, Harry Bush and Maris Gabalins in Latvia, Zygimantas Cepaitis ! 1623: in Lithuania, Peter Suchkow and Andrew Chernov in Russia, and ! 1624: Alexander Smishlajev in Esperantujo. Peter Gutmann offered to ! 1625: translate it into New Zealand English, but we finally decided PGP ! 1626: could get by with US English. ! 1627: ! 1628: Jean-loup Gailly, Mark Adler, and Richard B. Wales published the ZIP ! 1629: compression code, and granted permission for inclusion into PGP. The ! 1630: MD5 routines were developed and placed in the public domain by Ron ! 1631: Rivest. The IDEA(tm) cipher was developed by Xuejia Lai and James L. ! 1632: Massey at ETH in Zurich, and is used in PGP with permission from ! 1633: Ascom-Tech AG. ! 1634: ! 1635: Charlie Merritt originally taught me how to do decent multiprecision ! 1636: arithmetic for public key cryptography, and Jimmy Upton contributed a ! 1637: faster multiply/modulo algorithm. Thad Smith implemented an even ! 1638: faster modmult algorithm. Zhahai Stewart contributed a lot of useful ! 1639: ideas on PGP file formats and other stuff, including having more than ! 1640: one user ID for a key. I heard the idea of introducers from Whit ! 1641: Diffie. Kelly Goen did most of the work for the initial electronic ! 1642: publication of PGP 1.0. ! 1643: ! 1644: Various contributions of coding effort also came from Colin Plumb, ! 1645: Derek Atkins, and Castor Fu. Other contributions of effort, coding ! 1646: or otherwise, have come from Hugh Miller, Eric Hughes, Tim May, ! 1647: Stephan Neuhaus, and too many others for me to remember right now. ! 1648: Zbigniew Fiedorwicz did a Macintosh port. ! 1649: ! 1650: Since the release of PGP 2.0, many other programmers have sent in ! 1651: patches and bug fixes and porting adjustments for other computers. ! 1652: There are too many to individually thank here. ! 1653: ! 1654: The development of PGP has turned into a remarkable social ! 1655: phenomenon, whose unique political appeal has inspired the collective ! 1656: efforts of an ever-growing number of volunteer programmers. Remember ! 1657: that children's story called "Stone Soup"? It is getting harder to ! 1658: peer through the thick soup to see the stone at the bottom of the pot ! 1659: that I dropped in to start it all off. ! 1660: ! 1661: ! 1662: ! 1663: About the Author ! 1664: ================ ! 1665: ! 1666: Philip Zimmermann is a software engineer consultant with 19 years ! 1667: experience, specializing in embedded real-time systems, cryptography, ! 1668: authentication, and data communications. Experience includes design ! 1669: and implementation of authentication systems for financial ! 1670: information networks, network data security, key management ! 1671: protocols, embedded real-time multitasking executives, operating ! 1672: systems, and local area networks. ! 1673: ! 1674: Custom versions of cryptography and authentication products and ! 1675: public key implementations such as the NIST DSS are available from ! 1676: Zimmermann, as well as custom product development services. His ! 1677: consulting firm's address is: ! 1678: ! 1679: Boulder Software Engineering ! 1680: 3021 Eleventh Street ! 1681: Boulder, Colorado 80304 USA ! 1682: Phone: 303-541-0140 (10:00am - 7:00pm Mountain Time) ! 1683: Fax: arrange by phone ! 1684: Internet: [email protected]
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