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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 I: Essential 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 1990-1992 Philip Zimmermann. ! 37: For information on PGP licensing, distribution, copyrights, patents, ! 38: trademarks, liability limitations, and export controls, see the ! 39: "Legal Issues" section in the "PGP User's Guide, Volume II: Special ! 40: Topics". ! 41: ! 42: ! 43: Contents ! 44: ======== ! 45: ! 46: Quick Overview ! 47: Why Do You Need PGP? ! 48: How it Works ! 49: Installing PGP ! 50: How to Use PGP ! 51: To See a Usage Summary ! 52: Encrypting a Message ! 53: Encrypting a Message to Multiple Recipients ! 54: Signing a Message ! 55: Signing and then Encrypting ! 56: Using Just Conventional Encryption ! 57: Decrypting and Checking Signatures ! 58: Managing Keys ! 59: RSA Key Generation ! 60: Adding a Key to Your Key Ring ! 61: Removing a Key or User ID from Your Key Ring ! 62: Extracting (copying) a Key from Your Key Ring ! 63: Viewing the Contents of Your Key Ring ! 64: How to Protect Public Keys from Tampering ! 65: How Does PGP Keep Track of Which Keys are Valid? ! 66: How to Protect Secret Keys from Disclosure ! 67: Revoking a Public Key ! 68: What If You Lose Your Secret Key? ! 69: Advanced Topics ! 70: Sending Ciphertext Through E-mail Channels: Radix-64 Format ! 71: Environmental Variable for Path Name ! 72: Setting Configuration Parameters: CONFIG.TXT ! 73: Vulnerabilities ! 74: Beware of Snake Oil ! 75: PGP Quick Reference ! 76: Legal Issues ! 77: Acknowledgments ! 78: About the Author ! 79: ! 80: ! 81: Quick Overview ! 82: ============= ! 83: ! 84: Pretty Good(tm) Privacy (PGP), from Phil's Pretty Good Software, is a ! 85: high security cryptographic software application for MSDOS, Unix, ! 86: VAX/VMS, and other computers. PGP allows people to exchange files or ! 87: messages with privacy, authentication, and convenience. Privacy ! 88: means that only those intended to receive a message can read it. ! 89: Authentication means that messages that appear to be from a ! 90: particular person can only have originated from that person. ! 91: Convenience means that privacy and authentication are provided ! 92: without the hassles of managing keys associated with conventional ! 93: cryptographic software. No secure channels are needed to exchange ! 94: keys between users, which makes PGP much easier to use. This is ! 95: because PGP is based on a powerful new technology called "public key" ! 96: cryptography. ! 97: ! 98: PGP combines the convenience of the Rivest-Shamir-Adleman (RSA) ! 99: public key cryptosystem with the speed of conventional cryptography, ! 100: message digests for digital signatures, data compression before ! 101: encryption, good ergonomic design, and sophisticated key management. ! 102: And PGP performs the public-key functions faster than most other ! 103: software implementations. PGP is public key cryptography for the ! 104: masses. ! 105: ! 106: PGP does not provide any built-in modem communications capability. ! 107: You must use a separate software product for that. ! 108: ! 109: This document, "Volume I: Essential Topics", only explains the ! 110: essential concepts for using PGP, and should be read by all PGP ! 111: users. "Volume II: Special Topics" covers the advanced features of ! 112: PGP and other special topics, and may be read by more serious PGP ! 113: users. Neither volume explains the underlying technology details of ! 114: cryptographic algorithms and data structures. ! 115: ! 116: ! 117: Why Do You Need PGP? ! 118: ==================== ! 119: ! 120: It's personal. It's private. And it's no one's business but yours. ! 121: You may be planning a political campaign, discussing your taxes, or ! 122: having an illicit affair. Or you may be doing something that you ! 123: feel shouldn't be illegal, but is. Whatever it is, you don't want ! 124: your private electronic mail (E-mail) or confidential documents read ! 125: by anyone else. There's nothing wrong with asserting your privacy. ! 126: Privacy is as apple-pie as the Constitution. ! 127: ! 128: Perhaps you think your E-mail is legitimate enough that encryption is ! 129: unwarranted. If you really are a law-abiding citizen with nothing to ! 130: hide, then why don't you always send your paper mail on postcards? ! 131: Why not submit to drug testing on demand? Why require a warrant for ! 132: police searches of your house? Are you trying to hide something? ! 133: You must be a subversive or a drug dealer if you hide your mail ! 134: inside envelopes. Or maybe a paranoid nut. Do law-abiding citizens ! 135: have any need to encrypt their E-mail? ! 136: ! 137: What if everyone believed that law-abiding citizens should use ! 138: postcards for their mail? If some brave soul tried to assert his ! 139: privacy by using an envelope for his mail, it would draw suspicion. ! 140: Perhaps the authorities would open his mail to see what he's hiding. ! 141: Fortunately, we don't live in that kind of world, because everyone ! 142: protects most of their mail with envelopes. So no one draws suspicion ! 143: by asserting their privacy with an envelope. There's safety in ! 144: numbers. Analogously, it would be nice if everyone routinely used ! 145: encryption for all their E-mail, innocent or not, so that no one drew ! 146: suspicion by asserting their E-mail privacy with encryption. Think ! 147: of it as a form of solidarity. ! 148: ! 149: Today, if the Government wants to violate the privacy of ordinary ! 150: citizens, it has to expend a certain amount of expense and labor to ! 151: intercept and steam open and read paper mail, and listen to and ! 152: possibly transcribe spoken telephone conversation. This kind of ! 153: labor-intensive monitoring is not practical on a large scale. This ! 154: is only done in important cases when it seems worthwhile. ! 155: ! 156: More and more of our private communications are being routed through ! 157: electronic channels. Electronic mail will gradually replace ! 158: conventional paper mail. E-mail messages are just too easy to ! 159: intercept and scan for interesting keywords. This can be done ! 160: easily, routinely, automatically, and undetectably on a grand scale. ! 161: International cablegrams are already scanned this way on a large ! 162: scale by the NSA. ! 163: ! 164: We are moving toward a future when the nation will be crisscrossed ! 165: with high capacity fiber optic data networks linking together all our ! 166: increasingly ubiquitous personal computers. E-mail will be the norm ! 167: for everyone, not the novelty it is today. Perhaps the Government ! 168: will protect our E-mail with Government-designed encryption ! 169: protocols. Probably most people will trust that. But perhaps some ! 170: people will prefer their own protective measures. ! 171: ! 172: Senate Bill 266, a 1991 omnibus anti-crime bill, had an unsettling ! 173: measure buried in it. If this non binding resolution had become real ! 174: law, it would have forced manufacturers of secure communications ! 175: equipment to insert special "trap doors" in their products, so that ! 176: the Government can read anyone's encrypted messages. It reads: "It ! 177: is the sense of Congress that providers of electronic communications ! 178: services and manufacturers of electronic communications service ! 179: equipment shall insure that communications systems permit the ! 180: Government to obtain the plain text contents of voice, data, and ! 181: other communications when appropriately authorized by law." This ! 182: measure was defeated after rigorous protest from civil libertarians ! 183: and industry groups. But the Government has since introduced other ! 184: disturbing legislation to work toward similar objectives. ! 185: ! 186: If privacy is outlawed, only outlaws will have privacy. Intelligence ! 187: agencies have access to good cryptographic technology. So do the big ! 188: arms and drug traffickers. So do defense contractors, oil companies, ! 189: and other corporate giants. But ordinary people and grassroots ! 190: political organizations mostly have not had access to affordable ! 191: "military grade" public-key cryptographic technology. Until now. ! 192: ! 193: PGP empowers people to take their privacy into their own hands. ! 194: There's a growing social need for it. That's why I wrote it. ! 195: ! 196: ! 197: How it Works ! 198: ============ ! 199: ! 200: It would help if you were already familiar with the concept of ! 201: cryptography in general and public key cryptography in particular. ! 202: Nonetheless, here are a few introductory remarks about public key ! 203: cryptography. ! 204: ! 205: First, some elementary terminology. Suppose I want to send you a ! 206: message, but I don't want anyone but you to be able to read it. I ! 207: can "encrypt", or "encipher" the message, which means I scramble it ! 208: up in a hopelessly complicated way, rendering it unreadable to anyone ! 209: except you, the intended recipient of the message. I supply a ! 210: cryptographic "key" to encrypt the message, and you have to use the ! 211: same key to decipher or "decrypt" it. At least that's how it works ! 212: in conventional "single-key" cryptosystems. ! 213: ! 214: In conventional cryptosystems, such as the US Federal Data Encryption ! 215: Standard (DES), a single key is used for both encryption and ! 216: decryption. This means that a key must be initially transmitted via ! 217: secure channels so that both parties can know it before encrypted ! 218: messages can be sent over insecure channels. This may be ! 219: inconvenient. If you have a secure channel for exchanging keys, then ! 220: why do you need cryptography in the first place? ! 221: ! 222: In public key cryptosystems, everyone has two related complementary ! 223: keys, a publicly revealed key and a secret key. Each key unlocks the ! 224: code that the other key makes. Knowing the public key does not help ! 225: you deduce the corresponding secret key. The public key can be ! 226: published and widely disseminated across a communications network. ! 227: This protocol provides privacy without the need for the same kind of ! 228: secure channels that a conventional cryptosystem requires. ! 229: ! 230: Anyone can use a recipient's public key to encrypt a message to that ! 231: person, and that recipient uses her own corresponding secret key to ! 232: decrypt that message. No one but the recipient can decrypt it, ! 233: because no one else has access to that secret key. Not even the ! 234: person who encrypted the message can decrypt it. ! 235: ! 236: Message authentication is also provided. The sender's own secret key ! 237: can be used to encrypt a message, thereby "signing" it. This creates ! 238: a digital signature of a message, which the recipient (or anyone ! 239: else) can check by using the sender's public key to decrypt it. This ! 240: proves that the sender was the true originator of the message, and ! 241: that the message has not been subsequently altered by anyone else, ! 242: because the sender alone possesses the secret key that made that ! 243: signature. Forgery of a signed message is infeasible, and the sender ! 244: cannot later disavow his signature. ! 245: ! 246: These two processes can be combined to provide both privacy and ! 247: authentication by first signing a message with your own secret key, ! 248: then encrypting the signed message with the recipient's public key. ! 249: The recipient reverses these steps by first decrypting the message ! 250: with her own secret key, then checking the enclosed signature with ! 251: your public key. These steps are done automatically by the ! 252: recipient's software. ! 253: ! 254: Because the public key encryption algorithm is much slower than ! 255: conventional single-key encryption, encryption is better accomplished ! 256: by using a high-quality fast conventional single-key encryption ! 257: algorithm to encipher the message. This original unenciphered ! 258: message is called "plaintext". In a process invisible to the user, a ! 259: temporary random key, created just for this one "session", is used to ! 260: conventionally encipher the plaintext file. Then the recipient's ! 261: public key is used to encipher this temporary random conventional ! 262: key. This public-key-enciphered conventional "session" key is sent ! 263: along with the enciphered text (called "ciphertext") to the ! 264: recipient. The recipient uses her own secret key to recover this ! 265: temporary session key, and then uses that key to run the fast ! 266: conventional single-key algorithm to decipher the large ciphertext ! 267: message. ! 268: ! 269: Public keys are kept in individual "key certificates" that include ! 270: the key owner's user ID (which is that person's name), a timestamp of ! 271: when the key pair was generated, and the actual key material. Public ! 272: key certificates contain the public key material, while secret key ! 273: certificates contain the secret key material. Each secret key is ! 274: also encrypted with its own password, in case it gets stolen. A key ! 275: file, or "key ring" contains one or more of these key certificates. ! 276: Public key rings contain public key certificates, and secret key ! 277: rings contain secret key certificates. ! 278: ! 279: The keys are also internally referenced by a "key ID", which is an ! 280: "abbreviation" of the public key (the least significant 64 bits of ! 281: the large public key). When this key ID is displayed, only the lower ! 282: 24 bits are shown for further brevity. While many keys may share the ! 283: same user ID, for all practical purposes no two keys share the same ! 284: key ID. ! 285: ! 286: PGP uses "message digests" to form signatures. A message digest is a ! 287: 128-bit cryptographically strong one-way hash function of the ! 288: message. It is somewhat analogous to a "checksum" or CRC error ! 289: checking code, in that it compactly "represents" the message and is ! 290: used to detect changes in the message. Unlike a CRC, however, it is ! 291: computationally infeasible for an attacker to devise a substitute ! 292: message that would produce an identical message digest. The message ! 293: digest gets encrypted by the secret key to form a signature. ! 294: ! 295: Documents are signed by prefixing them with signature certificates, ! 296: which contain the key ID of the key that was used to sign it, a ! 297: secret-key-signed message digest of the document, and a timestamp of ! 298: when the signature was made. The key ID is used by the receiver to ! 299: look up the sender's public key to check the signature. The ! 300: receiver's software automatically looks up the sender's public key ! 301: and user ID in the receiver's public key ring. ! 302: ! 303: Encrypted files are prefixed by the key ID of the public key used to ! 304: encrypt them. The receiver uses this key ID message prefix to look ! 305: up the secret key needed to decrypt the message. The receiver's ! 306: software automatically looks up the necessary secret decryption key ! 307: in the receiver's secret key ring. ! 308: ! 309: These two types of key rings are the principal method of storing and ! 310: managing public and secret keys. Rather than keep individual keys in ! 311: separate key files, they are collected in key rings to facilitate the ! 312: automatic lookup of keys either by key ID or by user ID. Each user ! 313: keeps his own pair of key rings. An individual public key is ! 314: temporarily kept in a separate file long enough to send to your ! 315: friend who will then add it to her key ring. ! 316: ! 317: ! 318: ! 319: Installing PGP ! 320: ============== ! 321: ! 322: The MSDOS PGP 2.2 release comes in a compressed archive file called ! 323: PGP22.ZIP (each new release will have a name in the form "PGPxy.ZIP" ! 324: for PGP version number x.y). The archive can be decompressed with ! 325: the MSDOS shareware decompression utility PKUNZIP, or the Unix ! 326: utility "unzip". The PGP release package contains a README.DOC file ! 327: that you should always read before installing PGP. This README.DOC ! 328: file contains late-breaking news on what's new in this release of ! 329: PGP, as well as information on what's in all the other files included ! 330: in the release. ! 331: ! 332: If you already have PGP version 1.0 for MSDOS, you should probably ! 333: delete it, because no one else uses it anymore. If you don't want to ! 334: delete it, rename the old executable file to pgp1.exe, to avoid name ! 335: conflicts with the new PGP. ! 336: ! 337: To install PGP on your MSDOS system, you just have to copy the ! 338: compressed archive PGPxx.ZIP file into a suitable directory on your ! 339: hard disk (like C:\PGP), and decompress it with PKUNZIP. For best ! 340: results, you will also modify your AUTOEXEC.BAT file, as described ! 341: elsewhere in this manual, but you can do that later, after you've ! 342: played with PGP a bit and read more of this manual. If you haven't ! 343: run PGP before, the first step after installation (and reading this ! 344: manual) is to run the PGP key generation command "pgp -kg". ! 345: ! 346: Installing on Unix and VAX/VMS is generally similar to installing on ! 347: MSDOS, but you may have to compile the source code first. A Unix ! 348: makefile is provided with the source release for this purpose. ! 349: ! 350: For further details on installation, see the separate PGP ! 351: Installation Guide, in the file SETUP.DOC included with this ! 352: release. It fully describes how to set up the PGP directory and your ! 353: AUTOEXEC.BAT file and how to use PKUNZIP to install it. ! 354: ! 355: ! 356: ! 357: How to Use PGP ! 358: ============== ! 359: ! 360: ! 361: To See a Usage Summary ! 362: ---------------------- ! 363: ! 364: To see a quick command usage summary for PGP, just type: ! 365: ! 366: pgp -h ! 367: ! 368: ! 369: ! 370: Encrypting a Message ! 371: -------------------- ! 372: ! 373: To encrypt a plaintext file with the recipient's public key, type: ! 374: ! 375: pgp -e textfile her_userid ! 376: ! 377: This command produces a ciphertext file called textfile.pgp. A ! 378: specific example is: ! 379: ! 380: pgp -e letter.txt Alice ! 381: or: ! 382: pgp -e letter.txt "Alice S" ! 383: ! 384: The first example searches your public key ring file "pubring.pgp" ! 385: for any public key certificates that contain the string "Alice" ! 386: anywhere in the user ID field. The second example would find any ! 387: user IDs that contain "Alice S". You can't use spaces in the string ! 388: on the command line unless you enclose the whole string in quotes. ! 389: The search is not case-sensitive. If it finds a matching public key, ! 390: it uses it to encrypt the plaintext file "letter.txt", producing a ! 391: ciphertext file called "letter.pgp". ! 392: ! 393: PGP attempts to compress the plaintext before encrypting it, thereby ! 394: greatly enhancing resistance to cryptanalysis. Thus the ciphertext ! 395: file will likely be smaller than the plaintext file. ! 396: ! 397: If you want to send this encrypted message through E-mail channels, ! 398: convert it into printable ASCII "radix-64" format by adding the -a ! 399: option, as described later. ! 400: ! 401: ! 402: ! 403: Encrypting a Message to Multiple Recipients ! 404: ------------------------------------------- ! 405: ! 406: If you want to send the same message to more than one person, you may ! 407: specify encryption for several recipients, any of whom may decrypt the ! 408: same ciphertext file. To specify multiple recipients, just add more ! 409: user IDs to the command line, like so: ! 410: ! 411: pgp -e letter.txt Alice Bob Carol ! 412: ! 413: This would create a ciphertext file called letter.pgp that could be ! 414: decrypted by Alice or Bob or Carol. Any number of recipients may be ! 415: specified. ! 416: ! 417: ! 418: ! 419: Signing a Message ! 420: ----------------- ! 421: ! 422: To sign a plaintext file with your secret key, type: ! 423: ! 424: pgp -s textfile [-u your_userid] ! 425: ! 426: Note that [brackets] denote an optional field, so don't actually type ! 427: real brackets. ! 428: ! 429: This command produces a signed file called textfile.pgp. A specific ! 430: example is: ! 431: ! 432: pgp -s letter.txt -u Bob ! 433: ! 434: This searches your secret key ring file "secring.pgp" for any secret ! 435: key certificates that contain the string "Bob" anywhere in the user ! 436: ID field. The search is not case-sensitive. If it finds a matching ! 437: secret key, it uses it to sign the plaintext file "letter.txt", ! 438: producing a signature file called "letter.pgp". ! 439: ! 440: If you leave off the user ID field, the first key on your secret ! 441: key ring is used as the default secret key for your signature. ! 442: ! 443: ! 444: ! 445: Signing and then Encrypting ! 446: --------------------------- ! 447: ! 448: To sign a plaintext file with your secret key, and then encrypt it ! 449: with the recipient's public key: ! 450: ! 451: pgp -es textfile her_userid [-u your_userid] ! 452: ! 453: Note that [brackets] denote an optional field, so don't actually type ! 454: real brackets. ! 455: ! 456: This example produces a nested ciphertext file called textfile.pgp. ! 457: Your secret key to create the signature is automatically looked up in ! 458: your secret key ring via your_userid. Her public encryption key is ! 459: automatically looked up in your public key ring via her_userid. If ! 460: you leave off her user ID field from the command line, you will be ! 461: prompted for it. ! 462: ! 463: If you leave off your own user ID field, the first key on your secret ! 464: key ring is be used as the default secret key for your signature. ! 465: ! 466: Note that PGP attempts to compress the plaintext before encrypting ! 467: it. ! 468: ! 469: If you want to send this encrypted message through E-mail channels, ! 470: convert it into printable ASCII "radix-64" format by adding the -a ! 471: option, as described later. ! 472: ! 473: Multiple recipients may be specified by adding more user IDs to the ! 474: command line. ! 475: ! 476: ! 477: ! 478: Using Just Conventional Encryption ! 479: ---------------------------------- ! 480: ! 481: Sometimes you just need to encrypt a file the old-fashioned way, with ! 482: conventional single-key cryptography. This approach is useful for ! 483: protecting archive files that will be stored but will not be sent to ! 484: anyone else. Since the same person that encrypted the file will also ! 485: decrypt the file, public key cryptography is not really necessary. ! 486: ! 487: To encrypt a plaintext file with just conventional cryptography, ! 488: type: ! 489: ! 490: pgp -c textfile ! 491: ! 492: This example encrypts the plaintext file called textfile, producing a ! 493: ciphertext file called textfile.pgp, without using public key ! 494: cryptography, key rings, user IDs, or any of that stuff. It prompts ! 495: you for a pass phrase to use as a conventional key to encipher the ! 496: file. This pass phrase need not be (and, indeed, SHOULD not be) the ! 497: same pass phrase that you use to protect your own secret key. Note ! 498: that PGP attempts to compress the plaintext before encrypting it. ! 499: ! 500: PGP will not encrypt the same plaintext the same way twice, even if ! 501: you used the same pass phrase every time. ! 502: ! 503: ! 504: ! 505: Decrypting and Checking Signatures ! 506: ---------------------------------- ! 507: ! 508: To decrypt an encrypted file, or to check the signature integrity of a ! 509: signed file: ! 510: ! 511: pgp ciphertextfile [-o plaintextfile] ! 512: ! 513: Note that [brackets] denote an optional field, so don't actually type ! 514: real brackets. ! 515: ! 516: The ciphertext file name is assumed to have a default extension of ! 517: ".pgp". The optional plaintext output file name specifies where to ! 518: put processed plaintext output. If no name is specified, the ! 519: ciphertext filename is used, with no extension. If a signature is ! 520: nested inside of an encrypted file, it is automatically decrypted and ! 521: the signature integrity is checked. The full user ID of the signer ! 522: is displayed. ! 523: ! 524: Note that the "unwrapping" of the ciphertext file is completely ! 525: automatic, regardless of whether the ciphertext file is just signed, ! 526: just encrypted, or both. PGP uses the key ID prefix in the ! 527: ciphertext file to automatically find the appropriate secret ! 528: decryption key on your secret key ring. If there is a nested ! 529: signature, PGP then uses the key ID prefix in the nested signature to ! 530: automatically find the appropriate public key on your public key ring ! 531: to check the signature. If all the right keys are already present on ! 532: your key rings, no user intervention is required, except that you ! 533: will be prompted for your password for your secret key if necessary. ! 534: If the ciphertext file was conventionally encrypted without public ! 535: key cryptography, PGP recognizes this and prompts you for the pass ! 536: phrase to conventionally decrypt it. ! 537: ! 538: ! 539: Managing Keys ! 540: ============= ! 541: ! 542: Since the time of Julius Caesar, key management has always been the ! 543: hardest part of cryptography. One of the principal distinguishing ! 544: features of PGP is its sophisticated key management. ! 545: ! 546: ! 547: ! 548: RSA Key Generation ! 549: ------------------ ! 550: ! 551: To generate your own unique public/secret key pair of a specified ! 552: size, type: ! 553: ! 554: pgp -kg ! 555: ! 556: PGP shows you a menu of recommended key sizes (casual grade, ! 557: commercial grade, or military grade) and prompts you for what size ! 558: key you want, up to around a thousand bits. The bigger the key, the ! 559: more security you get, but you pay a price in speed. ! 560: ! 561: It also asks for a user ID, which means your name. It's a good idea ! 562: to use your full name as your user ID, because then there is less ! 563: risk of other people using the wrong public key to encrypt messages ! 564: to you. Spaces and punctuation are allowed in the user ID. It would ! 565: help if you put your E-mail address in <angle brackets> after your ! 566: name, like so: ! 567: ! 568: Robert M. Smith <[email protected]> ! 569: ! 570: If you don't have an E-mail address, use your phone number or some ! 571: other unique information that would help ensure that your user ID is ! 572: unique. ! 573: ! 574: PGP also asks for a "pass phrase" to protect your secret key in case ! 575: it falls into the wrong hands. Nobody can use your secret key file ! 576: without this pass phrase. The pass phrase is like a password, except ! 577: that it can be a whole phrase or sentence with many words, spaces, ! 578: punctuation, or anything else you want in it. Don't lose this pass ! 579: phrase-- there's no way to recover it if you do lose it. This pass ! 580: phrase will be needed later every time you use your secret key. The ! 581: pass phrase is case-sensitive, and should not be too short or easy to ! 582: guess. It is never displayed on the screen. Don't leave it written ! 583: down anywhere where someone else can see it, and don't store it on ! 584: your computer. If you don't want a pass phrase (You fool!), just ! 585: press return (or enter) at the pass phrase prompt. ! 586: ! 587: The public/secret key pair is derived from large truly random numbers ! 588: derived from measuring the intervals between your keystrokes with a ! 589: fast timer. ! 590: ! 591: Note that RSA key generation is a VERY lengthy process. It may take ! 592: a few seconds for a small key on a fast processor, or quite a few ! 593: minutes for a large key on an old IBM PC/XT. ! 594: ! 595: The generated key pair will be placed on your public and secret key ! 596: rings. You can later use the -kx command option to extract (copy) ! 597: your new public key from your public key ring and place it in a ! 598: separate public key file suitable for distribution to your friends. ! 599: The public key file can be sent to your friends for inclusion in ! 600: their public key rings. Naturally, you keep your secret key file to ! 601: yourself, and you should include it on your secret key ring. Each ! 602: secret key on a key ring is individually protected with its own pass ! 603: phrase. ! 604: ! 605: Never give your secret key to anyone else. For the same reason, don't ! 606: make key pairs for your friends. Everyone should make their own key ! 607: pair. Always keep physical control of your secret key, and don't risk ! 608: exposing it by storing it on a remote timesharing computer. Keep it ! 609: on your own personal computer. ! 610: ! 611: ! 612: ! 613: Adding a Key to Your Key Ring ! 614: ----------------------------- ! 615: ! 616: To add a public or secret key file's contents to your public or ! 617: secret key ring (note that [brackets] denote an optional field): ! 618: ! 619: pgp -ka keyfile [keyring] ! 620: ! 621: The keyfile extension defaults to ".pgp". The optional keyring file ! 622: name defaults to "pubring.pgp" or "secring.pgp", depending on whether ! 623: the keyfile contains a public or a secret key. You may specify a ! 624: different key ring file name, with the extension defaulting to ! 625: ".pgp". ! 626: ! 627: If the key is already on your key ring, PGP will not add it again. ! 628: All of the keys in the keyfile are added to the keyring, except for ! 629: duplicates. If the key being added has attached signatures ! 630: certifying it, the signatures are added with the key. If the key is ! 631: already on your key ring, PGP just merges in any new certifying ! 632: signatures for that key that you don't already have on your key ring. ! 633: ! 634: ! 635: ! 636: Removing a Key or User ID from Your Key Ring ! 637: -------------------------------------------- ! 638: ! 639: To remove a key or a user ID from your public key ring: ! 640: ! 641: pgp -kr userid [keyring] ! 642: ! 643: This searches for the specified user ID in your key ring, and removes ! 644: it if it finds a match. Remember that any fragment of the user ID ! 645: will suffice for a match. The optional keyring file name is assumed ! 646: to be literally "pubring.pgp". It can be omitted, or you can specify ! 647: "secring.pgp" if you want to remove a secret key. You may specify a ! 648: different key ring file name. The default key ring extension is ! 649: ".pgp". ! 650: ! 651: If more than one user ID exists for this key, you will be asked if ! 652: you want to remove only the user ID you specified, while leaving the ! 653: key and its other user IDs intact. ! 654: ! 655: ! 656: ! 657: Extracting (copying) a Key from Your Key Ring ! 658: --------------------------------------------- ! 659: ! 660: To extract (copy) a key from your public or secret key ring: ! 661: ! 662: pgp -kx userid keyfile [keyring] ! 663: ! 664: This non-destructively copies the key specified by the user ID from ! 665: your public or secret key ring to the specified key file. This is ! 666: particularly useful if you want to give a copy of your public key to ! 667: someone else. ! 668: ! 669: If the key has any certifying signatures attached to it on your key ! 670: ring, they are copied off along with the key. ! 671: ! 672: If you want the extracted key represented in printable ASCII ! 673: characters suitable for email purposes, use the -kxa options. ! 674: ! 675: ! 676: ! 677: Viewing the Contents of Your Key Ring ! 678: ------------------------------------- ! 679: ! 680: To view the contents of your public key ring: ! 681: ! 682: pgp -kv[v] [userid] [keyring] ! 683: ! 684: This lists any keys in the key ring that match the specified user ID ! 685: substring. If you omit the user ID, all of the keys in the key ring ! 686: are listed. The optional keyring file name is assumed to be ! 687: "pubring.pgp". It can be omitted, or you can specify "secring.pgp" ! 688: if you want to list secret keys. If you want to specify a different ! 689: key ring file name, you can. The default key ring extension is ! 690: ".pgp". ! 691: ! 692: To see all the certifying signatures attached to each key, use the ! 693: -kvv option: ! 694: ! 695: pgp -kvv [userid] [keyring] ! 696: ! 697: If you want to specify a particular key ring file name, but want to ! 698: see all the keys in it, try this alternative approach: ! 699: ! 700: pgp keyfile ! 701: ! 702: With no command options specified, PGP lists all the keys in ! 703: keyfile.pgp, and also attempts to add them to your key ring if they ! 704: are not already on your key ring. ! 705: ! 706: ! 707: ! 708: How to Protect Public Keys from Tampering ! 709: ----------------------------------------- ! 710: ! 711: In a public key cryptosystem, you don't have to protect public keys ! 712: from exposure. In fact, it's better if they are widely disseminated. ! 713: But it is important to protect public keys from tampering, to make ! 714: sure that a public key really belongs to whom it appears to belong to. ! 715: This may be the most important vulnerability of a public-key ! 716: cryptosystem. Let's first look at a potential disaster, then at how ! 717: to safely avoid it with PGP. ! 718: ! 719: Suppose you wanted to send a private message to Alice. You download ! 720: Alice's public key certificate from an electronic bulletin board ! 721: system (BBS). You encrypt your letter to Alice with this public key ! 722: and send it to her through the BBS's E-mail facility. ! 723: ! 724: Unfortunately, unbeknownst to you or Alice, another user named ! 725: Charlie has infiltrated the BBS and generated a public key of his own ! 726: with Alice's user ID attached to it. He covertly substitutes his ! 727: bogus key in place of Alice's real public key. You unwittingly use ! 728: this bogus key belonging to Charlie instead of Alice's public key. ! 729: All looks normal because this bogus key has Alice's user ID. Now ! 730: Charlie can decipher the message intended for Alice because he has ! 731: the matching secret key. He may even re-encrypt the deciphered ! 732: message with Alice's real public key and send it on to her so that no ! 733: one suspects any wrongdoing. Furthermore, he can even make ! 734: apparently good signatures from Alice with this secret key because ! 735: everyone will use the bogus public key to check Alice's signatures. ! 736: ! 737: The only way to prevent this disaster is to prevent anyone from ! 738: tampering with public keys. If you got Alice's public key directly ! 739: from Alice, this is no problem. But that may be difficult if Alice ! 740: is a thousand miles away, or is currently unreachable. ! 741: ! 742: Perhaps you could get Alice's public key from a mutual trusted friend ! 743: David who knows he has a good copy of Alice's public key. David ! 744: could sign Alice's public key, vouching for the integrity of Alice's ! 745: public key. David would create this signature with his own secret ! 746: key. ! 747: ! 748: This would create a signed public key certificate, and would show ! 749: that Alice's key had not been tampered with. This requires you have a ! 750: known good copy of David's public key to check his signature. Perhaps ! 751: David could provide Alice with a signed copy of your public key also. ! 752: David is thus serving as an "introducer" between you and Alice. ! 753: ! 754: This signed public key certificate for Alice could be uploaded by ! 755: David or Alice to the BBS, and you could download it later. You ! 756: could then check the signature via David's public key and thus be ! 757: assured that this is really Alice's public key. No impostor can fool ! 758: you into accepting his own bogus key as Alice's because no one else ! 759: can forge signatures made by David. ! 760: ! 761: A widely trusted person could even specialize in providing this ! 762: service of "introducing" users to each other by providing signatures ! 763: for their public key certificates. This trusted person could be ! 764: regarded as a "key server", or as a "Certifying Authority". Any ! 765: public key certificates bearing the key server's signature could be ! 766: trusted as truly belonging to whom they appear to belong to. All ! 767: users who wanted to participate would need a known good copy of just ! 768: the key server's public key, so that the key server's signatures ! 769: could be verified. ! 770: ! 771: A trusted centralized key server or Certifying Authority is ! 772: especially appropriate for large impersonal centrally-controlled ! 773: corporate or government institutions. Some institutional ! 774: environments use hierarchies of Certifying Authorities. ! 775: ! 776: For more decentralized grassroots "guerrilla style" environments, ! 777: allowing all users to act as a trusted introducers for their friends ! 778: would probably work better than a centralized key server. PGP tends ! 779: to emphasize this organic decentralized non-institutional approach. ! 780: It better reflects the natural way humans interact on a personal ! 781: social level, and allows people to better choose who they can trust ! 782: for key management. ! 783: ! 784: This whole business of protecting public keys from tampering is the ! 785: single most difficult problem in practical public key applications. ! 786: It is the "Achilles heel" of public key cryptography, and a lot of ! 787: software complexity is tied up in solving this one problem. ! 788: ! 789: You should use a public key only after you are sure that it is a good ! 790: public key that has not been tampered with, and actually belongs to ! 791: the person it claims to. You can be sure of this if you got this ! 792: public key certificate directly from its owner, or if it bears the ! 793: signature of someone else that you trust, from whom you already have ! 794: a good public key. Also, the user ID should have the full name of ! 795: the key's owner, not just her first name. ! 796: ! 797: No matter how tempted you are-- and you will be tempted-- never, ! 798: NEVER give in to expediency and trust a public key you downloaded ! 799: from a bulletin board, unless it is signed by someone you trust. ! 800: That uncertified public key could have been tampered with by anyone, ! 801: maybe even by the system administrator of the bulletin board. ! 802: ! 803: If you are asked to sign someone else's public key certificate, make ! 804: certain that it really belongs to that person named in the user ID of ! 805: that public key certificate. This is because your signature on her ! 806: public key certificate is a promise by you that this public key ! 807: really belongs to her. Other people who trust you will accept her ! 808: public key because it bears your signature. It may be ill-advised to ! 809: rely on hearsay-- don't sign her public key unless you have ! 810: independent firsthand knowledge that it really belongs to her. ! 811: Preferably, you should sign it only if you got it directly from her. ! 812: ! 813: In order to sign a public key, you must be far more certain of that ! 814: key's ownership than if you merely want to use that key to encrypt a ! 815: message. To be convinced of a key's validity enough to use it, ! 816: certifying signatures from trusted introducers should suffice. But ! 817: to sign a key yourself, you should require your own independent ! 818: firsthand knowledge of who owns that key. Perhaps you could call the ! 819: key's owner on the phone and read the key file to her to get her to ! 820: confirm that the key you have really is her key-- and make sure you ! 821: really are talking to the right person. See the section called ! 822: "Verifying a Public Key Over the Phone" in the Special Topics volume ! 823: for further details. ! 824: ! 825: Bear in mind that your signature on a public key certificate does not ! 826: vouch for the integrity of that person, but only vouches for the ! 827: integrity (the ownership) of that person's public key. You aren't ! 828: risking your credibility by signing the public key of a sociopath, if ! 829: you were completely confident that the key really belonged to him. ! 830: Other people would accept that key as belonging to him because you ! 831: signed it (assuming they trust you), but they wouldn't trust that ! 832: key's owner. Trusting a key is not the same as trusting the key's ! 833: owner. ! 834: ! 835: Trust is not necessarily transferable; I have a friend who I trust ! 836: not to lie. He's a gullible person who trusts the President not to ! 837: lie. That doesn't mean I trust the President not to lie. This is ! 838: just common sense. If I trust Alice's signature on a key, and Alice ! 839: trusts Charlie's signature on a key, that does not imply that I have ! 840: to trust Charlie's signature on a key. ! 841: ! 842: It would be a good idea to keep your own public key on hand with a ! 843: collection of certifying signatures attached from a variety of ! 844: "introducers", in the hopes that most people will trust at least one ! 845: of the introducers who vouch for your own public key's validity. ! 846: You could post your key with its attached collection of certifying ! 847: signatures on various electronic bulletin boards. If you sign ! 848: someone else's public key, return it to them with your signature so ! 849: that they can add it to their own collection of credentials for their ! 850: own public key. ! 851: ! 852: PGP keeps track of which keys on your public key ring are properly ! 853: certified with signatures from introducers that you trust. All you ! 854: have to do is tell PGP which people you trust as introducers, and ! 855: certify their keys yourself with your own ultimately trusted key. ! 856: PGP can take it from there, automatically validating any other keys ! 857: that have been signed by your designated introducers. And of course ! 858: you may directly sign more keys yourself. More on this later. ! 859: ! 860: Make sure no one else can tamper with your own public key ring. ! 861: Checking a new signed public key certificate must ultimately depend ! 862: on the integrity of the trusted public keys that are already on your ! 863: own public key ring. Maintain physical control of your public key ! 864: ring, preferably on your own personal computer rather than on a ! 865: remote timesharing system, just as you would do for your secret key. ! 866: This is to protect it from tampering, not from disclosure. Keep a ! 867: trusted backup copy of your public key ring and your secret key ring ! 868: on write-protected media. ! 869: ! 870: Since your own trusted public key is used as a final authority to ! 871: directly or indirectly certify all the other keys on your key ring, ! 872: it is the most important key to protect from tampering. To detect ! 873: any tampering of your own ultimately-trusted public key, PGP can be ! 874: set up to automatically compare your public key against a backup copy ! 875: on write-protected media. For details, see the description of the ! 876: "-kc" key ring check command in the Special Topics volume. ! 877: ! 878: PGP generally assumes you will maintain physical security over your ! 879: system and your key rings, as well as your copy of PGP itself. If an ! 880: intruder can tamper with your disk, then in theory he can tamper with ! 881: PGP itself, rendering moot the safeguards PGP may have to detect ! 882: tampering with keys. ! 883: ! 884: One somewhat complicated way to protect your own whole public key ring ! 885: from tampering is to sign the whole ring with your own secret key. ! 886: You could do this by making a detached signature certificate of the ! 887: public key ring, by signing the ring with the "-sb" options (see the ! 888: section called "Separating Signatures from Messages" in the PGP ! 889: User's Guide, Special Topics volume). Unfortunately, you would still ! 890: have to keep a separate trusted copy of your own public key around to ! 891: check the signature you made. You couldn't rely on your own public ! 892: key stored on your public key ring to check the signature you made ! 893: for the whole ring, because that is part of what you're trying to ! 894: check. ! 895: ! 896: ! 897: ! 898: How Does PGP Keep Track of Which Keys are Valid? ! 899: ------------------------------------------------ ! 900: ! 901: Before you read this section, be sure to read the above section on ! 902: "How to Protect Public Keys from Tampering". ! 903: ! 904: PGP keeps track of which keys on your public key ring are properly ! 905: certified with signatures from introducers that you trust. All you ! 906: have to do is tell PGP which people you trust as introducers, and ! 907: certify their keys yourself with your own ultimately trusted key. ! 908: PGP can take it from there, automatically validating any other keys ! 909: that have been signed by your designated introducers. And of course ! 910: you may directly sign more keys yourself. ! 911: ! 912: There are two entirely separate criteria PGP uses to judge a public ! 913: key's usefulness-- don't get them confused: ! 914: ! 915: 1) Does the key actually belong to whom it appears to belong? ! 916: In other words, has it been certified with a trusted signature? ! 917: 2) Does it belong to someone you can trust to certify other keys? ! 918: ! 919: PGP can calculate the answer to the first question. To answer the ! 920: second question, PGP must be explicitly told by you, the user. When ! 921: you supply the answer to question 2, PGP can then calculate the ! 922: answer to question 1 for other keys signed by the introducer you ! 923: designated as trusted. ! 924: ! 925: Keys that have been certified by a trusted introducer are deemed ! 926: valid by PGP. The keys belonging to trusted introducers must ! 927: themselves be certified either by you or by other trusted ! 928: introducers. ! 929: ! 930: PGP also allows for the possibility of you having several shades of ! 931: trust for people to act as introducers. Your trust for a key's owner ! 932: to act as an introducer does not just reflect your estimation of ! 933: their personal integrity-- it should also reflect how competent you ! 934: think they are at understanding key management and using good ! 935: judgment in signing keys. You can designate a person to PGP as ! 936: unknown, untrusted, marginally trusted, or completely trusted to ! 937: certify other public keys. This trust information is stored on your ! 938: key ring with their key, but when you tell PGP to copy a key off your ! 939: key ring, PGP will not copy the trust information along with the key, ! 940: because your private opinions on trust are regarded as confidential. ! 941: ! 942: When PGP is calculating the validity of a public key, it examines the ! 943: trust level of all the attached certifying signatures. It computes a ! 944: weighted score of validity-- two marginally trusted signatures are ! 945: deemed as credible as one fully trusted signature. PGP's skepticism ! 946: is adjustable-- for example, you may tune PGP to require two fully ! 947: trusted signatures or three marginally trusted signatures to judge a ! 948: key as valid. ! 949: ! 950: Your own key is "axiomatically" valid to PGP, needing no introducer's ! 951: signature to prove its validity. PGP knows which public keys are ! 952: yours, by looking for the corresponding secret keys on the secret ! 953: key ring. PGP also assumes you ultimately trust yourself to certify ! 954: other keys. ! 955: ! 956: As time goes on, you will accumulate keys from other people that you ! 957: may want to designate as trusted introducers. Everyone else will ! 958: each choose their own trusted introducers. And everyone will ! 959: gradually accumulate and distribute with their key a collection of ! 960: certifying signatures from other people, with the expectation that ! 961: anyone receiving it will trust at least one or two of the signatures. ! 962: This will cause the emergence of a decentralized fault-tolerant web ! 963: of confidence for all public keys. ! 964: ! 965: This unique grass-roots approach contrasts sharply with Government ! 966: standard public key management schemes, such as Internet Privacy ! 967: Enhanced Mail (PEM), which are based on centralized control and ! 968: mandatory centralized trust. The standard schemes rely on a ! 969: hierarchy of Certifying Authorities who dictate who you must trust. ! 970: PGP's decentralized probabilistic method for determining public key ! 971: legitimacy is the centerpiece of its key management architecture. ! 972: PGP lets you alone choose who you trust, putting you at the top of ! 973: your own private certification pyramid. PGP is for people who prefer ! 974: to pack their own parachutes. ! 975: ! 976: ! 977: ! 978: How to Protect Secret Keys from Disclosure ! 979: ------------------------------------------ ! 980: ! 981: Protect your own secret key and your pass phrase carefully. Really, ! 982: really carefully. If your secret key is ever compromised, you'd ! 983: better get the word out quickly to all interested parties (good luck) ! 984: before someone else uses it to make signatures in your name. For ! 985: example, they could use it to sign bogus public key certificates, ! 986: which could create problems for many people, especially if your ! 987: signature is widely trusted. And of course, a compromise of your own ! 988: secret key could expose all messages sent to you. ! 989: ! 990: To protect your secret key, you can start by always keeping physical ! 991: control of your secret key. Keeping it on your personal computer at ! 992: home is OK, or keep it in your notebook computer that you can carry ! 993: with you. If you must use an office computer that you don't always ! 994: have physical control of, then keep your public and secret key rings ! 995: on a write-protected removable floppy disk, and don't leave it behind ! 996: when you leave the office. It wouldn't be a good idea to allow your ! 997: secret key to reside on a remote timesharing computer, such as a ! 998: remote dial-in Unix system. Someone could eavesdrop on your modem ! 999: line and capture your pass phrase, and then obtain your actual secret ! 1000: key from the remote system. You should only use your secret key on a ! 1001: machine that you have physical control over. ! 1002: ! 1003: Don't store your pass phrase anywhere on the computer that has your ! 1004: secret key file. Storing both the secret key and the pass phrase on ! 1005: the same computer is as dangerous as keeping your PIN in the same ! 1006: wallet as your Automatic Teller Machine bank card. You don't want ! 1007: somebody to get their hands on your disk containing both the pass ! 1008: phrase and the secret key file. It would be most secure if you just ! 1009: memorize your pass phrase and don't store it anywhere but your brain. ! 1010: If you feel you must write down your pass phrase, keep it well ! 1011: protected, perhaps even more well protected than the secret key file. ! 1012: ! 1013: And keep backup copies of your secret key ring-- remember, you have ! 1014: the only copy of your secret key, and losing it will render useless ! 1015: all the copies of your public key that you have spread throughout the ! 1016: world. ! 1017: ! 1018: The decentralized non-institutional approach PGP uses to manage ! 1019: public keys has its benefits, but unfortunately this also means we ! 1020: can't rely on a single centralized list of which keys have been ! 1021: compromised. This makes it a bit harder to contain the damage of a ! 1022: secret key compromise. You just have to spread the word and hope ! 1023: everyone hears about it. ! 1024: ! 1025: If the worst case happens-- your secret key and pass phrase are both ! 1026: compromised (hopefully you will find this out somehow)-- you will ! 1027: have to issue a "key compromise" certificate. This kind of ! 1028: certificate is used to warn other people to stop using your public ! 1029: key. You can use PGP to create such a certificate by using the "-kd" ! 1030: command. Then you must somehow send this compromise certificate to ! 1031: everyone else on the planet, or at least to all your friends and ! 1032: their friends, et cetera. Their own PGP software will install this ! 1033: key compromise certificate on their public key rings and will ! 1034: automatically prevent them from accidentally using your public key ! 1035: ever again. You can then generate a new secret/public key pair and ! 1036: publish the new public key. You could send out one package containing ! 1037: both your new public key and the key compromise certificate for your ! 1038: old key. ! 1039: ! 1040: ! 1041: ! 1042: Revoking a Public Key ! 1043: --------------------- ! 1044: ! 1045: Suppose your secret key and your pass phrase are somehow both ! 1046: compromised. You have to get the word out to the rest of the world, ! 1047: so that they will all stop using your public key. To do this, you ! 1048: will have to issue a "key compromise", or "key revocation" certificate ! 1049: to revoke your public key. ! 1050: ! 1051: To generate a certificate to revoke your own key, use the -kd ! 1052: command: ! 1053: ! 1054: pgp -kd your_userid ! 1055: ! 1056: This certificate bears your signature, made with the same key you are ! 1057: revoking. You should widely disseminate this key revocation ! 1058: certificate as soon as possible. Other people who receive it can add ! 1059: it to their public key rings, and their PGP software then ! 1060: automatically prevents them from accidentally using your old public ! 1061: key ever again. You can then generate a new secret/public key pair ! 1062: and publish the new public key. ! 1063: ! 1064: You may choose to revoke your key for some other reason than the ! 1065: compromise of a secret key. If so, you may still use the same ! 1066: mechanism to revoke it. ! 1067: ! 1068: ! 1069: ! 1070: What If You Lose Your Secret Key? ! 1071: --------------------------------- ! 1072: ! 1073: Normally, if you want to revoke your own secret key, you can use the ! 1074: "-kd" command to issue a revocation certificate, signed with your own ! 1075: secret key (see "Revoking a Public Key"). ! 1076: ! 1077: But what can you do if you lose your secret key, or if your secret ! 1078: key is destroyed? You can't revoke it yourself, because you must use ! 1079: your own secret key to revoke it, and you don't have it anymore. A ! 1080: future version of PGP will offer a more secure means of revoking keys ! 1081: in these circumstances, allowing trusted introducers to certify that ! 1082: a public key has been revoked. But for now, you will have to get the ! 1083: word out through whatever informal means you can, asking users to ! 1084: "disable" your public key on their own individual public key rings. ! 1085: ! 1086: Other users may disable your public key on their own public key rings ! 1087: by using the "-kd" command. If a user ID is specified that does not ! 1088: correspond to a secret key on the secret key ring, the -kd command ! 1089: will look for that user ID on the public key ring, and mark that ! 1090: public key as disabled. A disabled key may not be used to encrypt ! 1091: any messages, and may not be extracted from the key ring with the -kx ! 1092: command. It can still be used to check signatures, but a warning is ! 1093: displayed. And if the user tries to add the same key again to his ! 1094: key ring, it will not work because the disabled key is already on the ! 1095: key ring. These combined features will help curtail the further ! 1096: spread of a disabled key. ! 1097: ! 1098: If the specified public key is already disabled, the -kd command will ! 1099: ask if you want the key reenabled. ! 1100: ! 1101: ! 1102: Advanced Topics ! 1103: =============== ! 1104: ! 1105: Most of the "Advanced Topics" are covered in the "PGP User's Guide, ! 1106: Volume II: Special Topics". But here are a few topics that bear ! 1107: mentioning here. ! 1108: ! 1109: ! 1110: Sending Ciphertext Through E-mail Channels: Radix-64 Format ! 1111: ----------------------------------------------------------- ! 1112: ! 1113: Many electronic mail systems only allow messages made of ASCII text, ! 1114: not the 8-bit raw binary data that ciphertext is made of. To get ! 1115: around this problem, PGP supports ASCII radix-64 format for ! 1116: ciphertext messages, similar to the Internet Privacy-Enhanced Mail ! 1117: (PEM) format. This special format represents binary data by using ! 1118: only printable ASCII characters, so it is useful for transmitting ! 1119: binary encrypted data through 7-bit channels or for sending binary ! 1120: encrypted data as normal E-mail text. This format acts as a form of ! 1121: "transport armor", protecting it against corruption as it travels ! 1122: through intersystem gateways on Internet. It also appends a CRC to ! 1123: detect transmission errors. ! 1124: ! 1125: Radix-64 format converts the plaintext by expanding groups of 3 ! 1126: binary 8-bit bytes into 4 printable ASCII characters, so the file ! 1127: grows by about 33%. But this expansion isn't so bad when you ! 1128: consider that the file probably was compressed more than that by PGP ! 1129: before it was encrypted. ! 1130: ! 1131: To produce a ciphertext file in ASCII radix-64 format, just add the ! 1132: "a" option when encrypting or signing a message, like so: ! 1133: ! 1134: pgp -esa message.txt her_userid ! 1135: ! 1136: This example produces a ciphertext file called "message.asc" that ! 1137: contains data in a PEM-like ASCII radix-64 format. This file can be ! 1138: easily uploaded into a text editor through 7-bit channels for ! 1139: transmission as normal E-mail on Internet or any other E-mail ! 1140: network. ! 1141: ! 1142: Decrypting the radix-64 transport-armored message is no different than ! 1143: a normal decrypt. For example: ! 1144: ! 1145: pgp message ! 1146: ! 1147: PGP automatically looks for the ASCII file "message.asc" before it ! 1148: looks for the binary file "message.pgp". It recognizes that the file ! 1149: is in radix-64 format and converts it back to binary before ! 1150: processing as it normally does, producing as a by-product a ".pgp" ! 1151: ciphertext file in binary form. The final output file is in normal ! 1152: plaintext form, just as it was in the original file "message.txt". ! 1153: ! 1154: Most Internet E-mail facilities prohibit sending messages that are ! 1155: more than 50000 bytes long. Longer messages must be broken into ! 1156: smaller chunks that can be mailed separately. If your encrypted ! 1157: message is very large, and you requested radix-64 format, PGP ! 1158: automatically breaks it up into chunks that are each small enough to ! 1159: send via E-mail. The chunks are put into files named with extensions ! 1160: ".as1", ".as2", ".as3", etc. The recipient must concatenate these ! 1161: separate files back together in their proper order into one big file ! 1162: before decrypting it. While decrypting, PGP ignores any extraneous ! 1163: text in mail headers that are not enclosed in the radix-64 message ! 1164: blocks. ! 1165: ! 1166: If you want to send a public key to someone else in radix-64 format, ! 1167: just add the -a option while extracting the key from your keyring. ! 1168: ! 1169: If you forgot to use the -a option when you made a ciphertext file or ! 1170: extracted a key, you may still directly convert the binary file into ! 1171: radix-64 format by simply using the -a option alone, without any ! 1172: encryption specified. PGP converts it to a ".asc" file. ! 1173: ! 1174: If you want to send through an E-mail channel a plaintext file that ! 1175: is signed but not encrypted, PGP will normally convert it all into ! 1176: radix-64 armor, rendering it unreadable to the casual human observer. ! 1177: If the original plaintext message is in text (not binary) form, there ! 1178: is a way to send it through an E-mail channel in such a way that the ! 1179: ASCII armor is applied only to the binary signature certificate, but ! 1180: not to the plaintext message. This makes it possible for the ! 1181: recipient to read the signed message with human eyes, without the aid ! 1182: of PGP. Of course, PGP is still needed to actually check the ! 1183: signature. For further information on this feature, see the ! 1184: explanation of the CLEARSIG parameter in the section "Setting ! 1185: Configuration Parameters: CONFIG.TXT" in the Special Topics volume. ! 1186: ! 1187: ! 1188: Environmental Variable for Path Name ! 1189: ------------------------------------ ! 1190: ! 1191: PGP uses several special files for its purposes, such as your ! 1192: standard key ring files "pubring.pgp" and "secring.pgp", the random ! 1193: number seed file "randseed.bin", the PGP configuration file ! 1194: "config.txt", and the foreign language string translation file ! 1195: "language.txt". These special files can be kept in any directory, by ! 1196: setting the environmental variable "PGPPATH" to the desired pathname. ! 1197: For example, on MSDOS, the shell command: ! 1198: ! 1199: SET PGPPATH=C:\PGP ! 1200: ! 1201: makes PGP assume that your public key ring filename is ! 1202: "C:\PGP\pubring.pgp". Assuming, of course, that this directory ! 1203: exists. Use your favorite text editor to modify your MSDOS ! 1204: AUTOEXEC.BAT file to automatically set up this variable whenever you ! 1205: start up your system. If PGPPATH remains undefined, these special ! 1206: files are assumed to be in the current directory. ! 1207: ! 1208: ! 1209: ! 1210: Setting Configuration Parameters: CONFIG.TXT ! 1211: -------------------------------------------- ! 1212: ! 1213: PGP has a number of user-settable parameters that can be defined in a ! 1214: special configuration text file called "config.txt", in the directory ! 1215: pointed to by the shell environmental variable PGPPATH. Having a ! 1216: configuration file enables the user to define various flags and ! 1217: parameters for PGP without the burden of having to always define ! 1218: these parameters in the PGP command line. ! 1219: ! 1220: With these configuration parameters, for example, you can control ! 1221: where PGP stores its temporary scratch files, or you can select what ! 1222: foreign language PGP will use to display its diagnostics messages and ! 1223: user prompts, or you can adjust PGP's level of skepticism in ! 1224: determining a key's validity based on the number of certifying ! 1225: signatures it has. ! 1226: ! 1227: For more details on setting these configuration parameters, see the ! 1228: appropriate section of the PGP User's Guide, Special Topics volume. ! 1229: ! 1230: ! 1231: ! 1232: Vulnerabilities ! 1233: --------------- ! 1234: ! 1235: No data security system is impenetrable. PGP can be circumvented in ! 1236: a variety of ways. Potential vulnerabilities you should be aware of ! 1237: include compromising your pass phrase or secret key, public key ! 1238: tampering, files that you deleted but are still somewhere on the ! 1239: disk, viruses and Trojan horses, breaches in your physical security, ! 1240: electromagnetic emissions, exposure on multi-user systems, traffic ! 1241: analysis, and perhaps even direct cryptanalysis. ! 1242: ! 1243: For a detailed discussion of these issues, see the "Vulnerabilities" ! 1244: section in the PGP User's Guide, Special Topics volume. ! 1245: ! 1246: ! 1247: Beware of Snake Oil ! 1248: =================== ! 1249: ! 1250: When examining a cryptographic software package, the question always ! 1251: remains, why should you trust this product? Even if you examined the ! 1252: source code yourself, not everyone has the cryptographic experience ! 1253: to judge the security. Even if you are an experienced cryptographer, ! 1254: subtle weaknesses in the algorithms could still elude you. ! 1255: ! 1256: When I was in college in the early seventies, I devised what I ! 1257: believed was a brilliant encryption scheme. A simple pseudorandom ! 1258: number stream was added to the plaintext stream to create ! 1259: ciphertext. This would seemingly thwart any frequency analysis of ! 1260: the ciphertext, and would be uncrackable even to the most resourceful ! 1261: Government intelligence agencies. I felt so smug about my ! 1262: achievement. So cock-sure. ! 1263: ! 1264: Years later, I discovered this same scheme in several introductory ! 1265: cryptography texts and tutorial papers. How nice. Other ! 1266: cryptographers had thought of the same scheme. Unfortunately, the ! 1267: scheme was presented as a simple homework assignment on how to use ! 1268: elementary cryptanalytic techniques to trivially crack it. So much ! 1269: for my brilliant scheme. ! 1270: ! 1271: From this humbling experience I learned how easy it is to fall into a ! 1272: false sense of security when devising an encryption algorithm. Most ! 1273: people don't realize how fiendishly difficult it is to devise an ! 1274: encryption algorithm that can withstand a prolonged and determined ! 1275: attack by a resourceful opponent. Many mainstream software engineers ! 1276: have developed equally naive encryption schemes (often even the very ! 1277: same encryption scheme), and some of them have been incorporated into ! 1278: commercial encryption software packages and sold for good money to ! 1279: thousands of unsuspecting users. ! 1280: ! 1281: This is like selling automotive seat belts that look good and feel ! 1282: good, but snap open in even the slowest crash test. Depending on ! 1283: them may be worse than not wearing seat belts at all. No one ! 1284: suspects they are bad until a real crash. Depending on weak ! 1285: cryptographic software may cause you to unknowingly place sensitive ! 1286: information at risk. You might not otherwise have done so if you had ! 1287: no cryptographic software at all. Perhaps you may never even ! 1288: discover your data has been compromised. ! 1289: ! 1290: Sometimes commercial packages use the Federal Data Encryption ! 1291: Standard (DES), a good conventional algorithm recommended by the ! 1292: Government for commercial use (but not for classified information, ! 1293: oddly enough-- hmmm). There are several "modes of operation" the ! 1294: DES can use, some of them better than others. The Government ! 1295: specifically recommends not using the weakest simplest mode for ! 1296: messages, the Electronic Codebook (ECB) mode. But they do recommend ! 1297: the stronger and more complex Cipher Feedback (CFB) or Cipher Block ! 1298: Chaining (CBC) modes. ! 1299: ! 1300: Unfortunately, most of the commercial encryption packages I've looked ! 1301: at use ECB mode. When I've talked to the authors of a number of ! 1302: these implementations, they say they've never heard of CBC or CFB ! 1303: modes, and didn't know anything about the weaknesses of ECB mode. ! 1304: The very fact that they haven't even learned enough cryptography to ! 1305: know these elementary concepts is not reassuring. These same ! 1306: software packages often include a second faster encryption algorithm ! 1307: that can be used instead of the slower DES. The author of the ! 1308: package often thinks his proprietary faster algorithm is as secure as ! 1309: the DES, but after questioning him I usually discover that it's just ! 1310: a variation of my own brilliant scheme from college days. Or maybe ! 1311: he won't even reveal how his proprietary encryption scheme works, but ! 1312: assures me it's a brilliant scheme and I should trust it. I'm sure ! 1313: he believes that his algorithm is brilliant, but how can I know that ! 1314: without seeing it? ! 1315: ! 1316: In all fairness I must point out that in most cases these products do ! 1317: not come from companies that specialize in cryptographic technology. ! 1318: ! 1319: There is a company called AccessData (87 East 600 South, Orem, Utah ! 1320: 84058, phone 1-800-658-5199) that sells a package for $185 that ! 1321: cracks the built-in encryption schemes used by WordPerfect, Lotus ! 1322: 1-2-3, MS Excel, Symphony, Quattro Pro, Paradox, and MS Word 2.0. It ! 1323: doesn't simply guess passwords-- it does real cryptanalysis. Some ! 1324: people buy it when they forget their password for their own files. ! 1325: Law enforcement agencies buy it too, so they can read files they ! 1326: seize. I talked to Eric Thompson, the author, and he said his ! 1327: program only takes a split second to crack them, but he put in some ! 1328: delay loops to slow it down so it doesn't look so easy to the ! 1329: customer. He also told me that the password encryption feature of ! 1330: PKZIP files can often be easily broken, and that his law enforcement ! 1331: customers already have that service regularly provided to them from ! 1332: another vendor. ! 1333: ! 1334: In some ways, cryptography is like pharmaceuticals. Its integrity ! 1335: may be absolutely crucial. Bad penicillin looks the same as good ! 1336: penicillin. You can tell if your spreadsheet software is wrong, but ! 1337: how do you tell if your cryptography package is weak? The ciphertext ! 1338: produced by a weak encryption algorithm looks as good as ciphertext ! 1339: produced by a strong encryption algorithm. There's a lot of snake ! 1340: oil out there. A lot of quack cures. Unlike the patent medicine ! 1341: hucksters of old, these software implementors usually don't even know ! 1342: their stuff is snake oil. They may be good software engineers, but ! 1343: they usually haven't even read any of the academic literature in ! 1344: cryptography. But they think they can write good cryptographic ! 1345: software. And why not? After all, it seems intuitively easy to do ! 1346: so. And their software seems to work okay. ! 1347: ! 1348: Anyone who thinks they have devised an unbreakable encryption scheme ! 1349: either is an incredibly rare genius or is naive and inexperienced. ! 1350: ! 1351: I remember a conversation with Brian Snow, a highly placed senior ! 1352: cryptographer with the NSA. He said he would never trust an ! 1353: encryption algorithm designed by someone who had not "earned their ! 1354: bones" by first spending a lot of time cracking codes. That did make ! 1355: a lot of sense. I observed that practically no one in the commercial ! 1356: world of cryptography qualified under this criterion. "Yes", he said ! 1357: with a self assured smile, "And that makes our job at NSA so much ! 1358: easier." A chilling thought. I didn't qualify either. ! 1359: ! 1360: The Government has peddled snake oil too. After World War II, the US ! 1361: sold German Enigma ciphering machines to third world governments. ! 1362: But they didn't tell them that the Allies cracked the Enigma code ! 1363: during the war, a fact that remained classified for many years. Even ! 1364: today many Unix systems worldwide use the Enigma cipher for file ! 1365: encryption, in part because the Government has created legal ! 1366: obstacles against using better algorithms. They even tried to ! 1367: prevent the initial publication of the RSA algorithm in 1977. And ! 1368: they have squashed essentially all commercial efforts to develop ! 1369: effective secure telephones for the general public. ! 1370: ! 1371: The principle job of the US Government's National Security Agency is ! 1372: to gather intelligence, principally by covertly tapping into people's ! 1373: private communications (see James Bamford's book, "The Puzzle ! 1374: Palace"). The NSA has amassed considerable skill and resources for ! 1375: cracking codes. When people can't get good cryptography to protect ! 1376: themselves, it makes NSA's job much easier. NSA also has the ! 1377: responsibility of approving and recommending encryption algorithms. ! 1378: Some critics charge that this is a conflict of interest, like putting ! 1379: the fox in charge of guarding the hen house. NSA has been pushing a ! 1380: conventional encryption algorithm that they designed, and they won't ! 1381: tell anybody how it works because that's classified. They want ! 1382: others to trust it and use it. But any cryptographer can tell you ! 1383: that a well-designed encryption algorithm does not have to be ! 1384: classified to remain secure. Only the keys should need protection. ! 1385: How does anyone else really know if NSA's classified algorithm is ! 1386: secure? It's not that hard for NSA to design an encryption algorithm ! 1387: that only they can crack, if no one else can review the algorithm. ! 1388: Are they deliberately selling snake oil? ! 1389: ! 1390: I'm not as certain about the security of PGP as I once was about my ! 1391: brilliant encryption software from college. If I were, that would be ! 1392: a bad sign. But I'm pretty sure that PGP does not contain any ! 1393: glaring weaknesses. The crypto algorithms were developed by people ! 1394: at high levels of civilian cryptographic academia, and have been ! 1395: individually subject to extensive peer review. Source code is ! 1396: available to facilitate peer review of PGP and to help dispel the ! 1397: fears of some users. It's reasonably well researched, and has been ! 1398: years in the making. And I don't work for the NSA. I hope it ! 1399: doesn't require too large a "leap of faith" to trust the security of ! 1400: PGP. ! 1401: ! 1402: ! 1403: PGP Quick Reference ! 1404: =================== ! 1405: ! 1406: Here's a quick summary of PGP commands. ! 1407: ! 1408: ! 1409: To encrypt a plaintext file with the recipient's public key: ! 1410: pgp -e textfile her_userid ! 1411: ! 1412: To sign a plaintext file with your secret key: ! 1413: pgp -s textfile [-u your_userid] ! 1414: ! 1415: To sign a plaintext file with your secret key, and then encrypt it ! 1416: with the recipient's public key: ! 1417: pgp -es textfile her_userid [-u your_userid] ! 1418: ! 1419: To encrypt a plaintext file with just conventional cryptography, type: ! 1420: pgp -c textfile ! 1421: ! 1422: To decrypt an encrypted file, or to check the signature integrity of a ! 1423: signed file: ! 1424: pgp ciphertextfile [-o plaintextfile] ! 1425: ! 1426: To encrypt a message for any number of multiple recipients: ! 1427: pgp -e textfile userid1 userid2 userid3 ! 1428: ! 1429: --- Key management commands: ! 1430: ! 1431: To generate your own unique public/secret key pair: ! 1432: pgp -kg ! 1433: ! 1434: To add a public or secret key file's contents to your public or ! 1435: secret key ring: ! 1436: pgp -ka keyfile [keyring] ! 1437: ! 1438: To extract (copy) a key from your public or secret key ring: ! 1439: pgp -kx userid keyfile [keyring] ! 1440: or: pgp -kxa userid keyfile [keyring] ! 1441: ! 1442: To view the contents of your public key ring: ! 1443: pgp -kv[v] [userid] [keyring] ! 1444: ! 1445: To view the "fingerprint" of a public key, to help verify it over ! 1446: the telephone with its owner: ! 1447: pgp -kvc [userid] [keyring] ! 1448: ! 1449: To view the contents and check the certifying signatures of your ! 1450: public key ring: ! 1451: pgp -kc [userid] [keyring] ! 1452: ! 1453: To edit the userid or pass phrase for your secret key: ! 1454: pgp -ke userid [keyring] ! 1455: ! 1456: To edit the trust parameters for a public key: ! 1457: pgp -ke userid [keyring] ! 1458: ! 1459: To remove a key or just a userid from your public key ring: ! 1460: pgp -kr userid [keyring] ! 1461: ! 1462: To sign and certify someone else's public key on your public key ring: ! 1463: pgp -ks her_userid [-u your_userid] [keyring] ! 1464: ! 1465: To remove selected signatures from a userid on a keyring: ! 1466: pgp -krs userid [keyring] ! 1467: ! 1468: To permanently revoke your own key, issuing a key compromise ! 1469: certificate: ! 1470: pgp -kd your_userid ! 1471: ! 1472: To disable or reenable a public key on your own public key ring: ! 1473: pgp -kd userid ! 1474: ! 1475: --- Esoteric commands: ! 1476: ! 1477: To decrypt a message and leave the signature on it intact: ! 1478: pgp -d ciphertextfile ! 1479: ! 1480: To create a signature certificate that is detached from the document: ! 1481: pgp -sb textfile [-u your_userid] ! 1482: ! 1483: To detach a signature certificate from a signed message: ! 1484: pgp -b ciphertextfile ! 1485: ! 1486: --- Command options that can be used in combination with other ! 1487: command options (sometimes even spelling interesting words!): ! 1488: ! 1489: To produce a ciphertext file in ASCII radix-64 format, just add the ! 1490: -a option when encrypting or signing a message or extracting a key: ! 1491: pgp -sea textfile her_userid ! 1492: or: pgp -kxa userid keyfile [keyring] ! 1493: ! 1494: To wipe out the plaintext file after producing the ciphertext file, ! 1495: just add the -w (wipe) option when encrypting or signing a message: ! 1496: pgp -sew message.txt her_userid ! 1497: ! 1498: To specify that a plaintext file contains ASCII text, not binary, and ! 1499: should be converted to recipient's local text line conventions, add ! 1500: the -t (text) option to other options: ! 1501: pgp -seat message.txt her_userid ! 1502: ! 1503: To view the decrypted plaintext output on your screen (like the ! 1504: Unix-style "more" command), without writing it to a file, use ! 1505: the -m (more) option while decrypting: ! 1506: pgp -m ciphertextfile ! 1507: ! 1508: To specify that the recipient's decrypted plaintext will be shown ! 1509: ONLY on her screen and cannot be saved to disk, add the -m option: ! 1510: pgp -steam message.txt her_userid ! 1511: ! 1512: To recover the original plaintext filename while decrypting, add ! 1513: the -p option: ! 1514: pgp -p ciphertextfile ! 1515: ! 1516: To use a Unix-style filter mode, reading from standard input and ! 1517: writing to standard output, add the -f option: ! 1518: pgp -feast her_userid <inputfile >outputfile ! 1519: ! 1520: ! 1521: ! 1522: Legal Issues ! 1523: ============ ! 1524: ! 1525: For detailed information on PGP licensing, distribution, copyrights, ! 1526: patents, trademarks, liability limitations, and export controls, see ! 1527: the "Legal Issues" section in the "PGP User's Guide, Volume II: ! 1528: Special Topics". ! 1529: ! 1530: PGP uses a public key algorithm claimed by U.S. patent #4,405,829. ! 1531: The exclusive rights to this patent are held by a California company ! 1532: called Public Key Partners, and you may be infringing this patent if ! 1533: you use PGP in the USA. This is explained in the Volume II manual. ! 1534: ! 1535: PGP is "guerrilla" freeware, and I don't mind if you distribute it ! 1536: widely. Just don't ask me to send you a copy. Instead, you can get ! 1537: it yourself from many BBS systems and a number of Internet FTP sites. ! 1538: ! 1539: ! 1540: ! 1541: Acknowledgments ! 1542: ================ ! 1543: ! 1544: I'd like to thank the following people for their contributions to the ! 1545: creation of Pretty Good Privacy. Although I was the author of PGP ! 1546: version 1.0, major parts of later versions of PGP were implemented by ! 1547: an international collaborative effort involving a large number of ! 1548: contributors, under my design guidance. ! 1549: ! 1550: Branko Lankester, Hal Finney and Peter Gutmann all contributed a huge ! 1551: amount of time in adding features for PGP 2.0, and ported it to Unix ! 1552: variants. Hal and Branko made Herculean efforts in implementing my ! 1553: new key management protocols. Branko has spent more time on it than ! 1554: any other contributor to PGP. ! 1555: ! 1556: Hugh Kennedy ported it to VAX/VMS, Lutz Frank ported it to the Atari ! 1557: ST, and Cor Bosman and Colin Plumb ported it to the Commodore Amiga. ! 1558: ! 1559: Translation of PGP into foreign languages was done by Jean-loup ! 1560: Gailly in France, Armando Ramos in Spain, Felipe Rodriquez Svensson ! 1561: and Branko Lankester in The Netherlands, Miguel Angel Gallardo in ! 1562: Spain, Hugh Kennedy and Lutz Frank in Germany, David Vincenzetti in ! 1563: Italy, Harry Bush and Maris Gabalins in Latvia, Zygimantas Cepaitis ! 1564: in Lithuania, Peter Suchkow and Andrew Chernov in Russia, and ! 1565: Alexander Smishlajev in Esperantujo. Peter Gutmann offered to ! 1566: translate it into New Zealand English, but we finally decided PGP ! 1567: could get by with US English. ! 1568: ! 1569: Jean-loup Gailly, Mark Adler, and Richard B. Wales published the ZIP ! 1570: compression code, and granted permission for inclusion into PGP. The ! 1571: MD5 routines were developed and placed in the public domain by Ron ! 1572: Rivest. The IDEA(tm) cipher was developed by Xuejia Lai and James L. ! 1573: Massey at ETH in Zurich, and is used in PGP with permission from ! 1574: Ascom-Tech AG. ! 1575: ! 1576: Charlie Merritt originally taught me how to do decent multiprecision ! 1577: arithmetic for public key cryptography, and Jimmy Upton contributed a ! 1578: faster multiply/modulo algorithm. Thad Smith implemented an even ! 1579: faster modmult algorithm. Zhahai Stewart contributed a lot of useful ! 1580: ideas on PGP file formats and other stuff, including having more than ! 1581: one user ID for a key. I heard the idea of introducers from Whit ! 1582: Diffie. Kelly Goen did most of the work for the initial electronic ! 1583: publication of PGP 1.0. ! 1584: ! 1585: Various contributions of coding effort also came from Colin Plumb, ! 1586: Derek Atkins, and Castor Fu. Other contributions of effort, coding ! 1587: or otherwise, have come from Hugh Miller, Eric Hughes, Tim May, ! 1588: Stephan Neuhaus, and too many others for me to remember right now. ! 1589: Two Macintosh porting projects have been underway, headed by Zbigniew ! 1590: Fiedorwicz and Blair Weiss. ! 1591: ! 1592: Since the release of PGP 2.0, many other programmers have sent in ! 1593: patches and bug fixes and porting adjustments for other computers. ! 1594: There are too many to individually thank here. ! 1595: ! 1596: The development of PGP has turned into a remarkable social ! 1597: phenomenon, whose unique political appeal has inspired the collective ! 1598: efforts of an ever-growing number of volunteer programmers. Remember ! 1599: that children's story called "Stone Soup"? It is getting harder to ! 1600: peer through the thick soup to see the stone at the bottom of the pot ! 1601: that I dropped in to start it all off. ! 1602: ! 1603: ! 1604: ! 1605: About the Author ! 1606: ================ ! 1607: ! 1608: Philip Zimmermann is a software engineer consultant with 18 years ! 1609: experience, specializing in embedded real-time systems, cryptography, ! 1610: authentication, and data communications. Experience includes design ! 1611: and implementation of authentication systems for financial ! 1612: information networks, network data security, key management ! 1613: protocols, embedded real-time multitasking executives, operating ! 1614: systems, and local area networks. ! 1615: ! 1616: Custom versions of cryptography and authentication products and ! 1617: public key implementations such as the NIST DSS are available from ! 1618: Zimmermann, as well as custom product development services. His ! 1619: consulting firm's address is: ! 1620: ! 1621: Boulder Software Engineering ! 1622: 3021 Eleventh Street ! 1623: Boulder, Colorado 80304 USA ! 1624: Phone 303-541-0140 (voice or FAX) (10:00am - 7:00pm Mountain Time) ! 1625: Internet: [email protected] ! 1626: ! 1627: ! 1628:
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