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7. PGP

THE CYPHERNOMICON: Cypherpunks FAQ and More, Version 0.666, 1994-09-10, Copyright Timothy C. May. All rights reserved. See the detailed disclaimer. Use short sections under "fair use" provisions, with appropriate credit, but don't put your name on my words.

7.2. SUMMARY: PGP -- Pretty Good Privacy

7.2.1. Main Points

  • PGP is the most important crypto tool there is, having single-handedly spread public key methods around the world
    • many other tools are being built on top of it

7.2.2. Connections to Other Sections

  • ironically, almost no understanding of how PGP works in detail is needed; there are plenty of experts who specialize in that

7.2.3. Where to Find Additional Information

  • newsgroups carry up to date comments; just read them for a few weeks and many things will float by
    • various FAQs on PGP
    • even an entire book, by Simpson Garfinkel:
      • PGP: Pretty Good Privacy by Simson Garfinkel 1st Edition November 1994 (est.) 250 pages (est),ISBN: 1-56592-098-8, $17.95 (est)

7.2.4. Miscellaneous Comments

  • a vast number of ftp sites, URLs, etc., and these change
  • this document can't possibly stay current on these--see the pointers in the newsgroups for the most current sites

7.3. Introduction

7.3.1. Why does PGP rate its own section?

  • Like Clipper, PGP is too big a set of issues not to have its own section

7.3.2. "What's the fascination in Cypherpunks with PGP?"

  • Ironically, our first meeting, in September 1992, coincided within a few days of the release of PGP 2.0. Arthur Abraham provided diskettes of 2.0, complete with laser-printed labels. Version 2.0 was the first truly useful version of PGP (so I hear...I never tried Version 1.0, which had limited distribution). So PGP and Cypherpunks shared a history--and Phil Zimmermann has been to some physical meetings.
  • A practical, usable, understandable tool. Fairly easy to use. In contrast, many other developments are more abstract and do not lend themselves to use by hobbyists and amateurs. This alone ensures PGP an honored place (and might be an object lesson for developers of other tools).

7.3.3. The points here focus on PGP, but may apply as well to similar crypto programs, such as commercial RSA packages (integrated into mailers, commercial programs, etc.).

7.4. What is PGP?

7.4.1. "What is PGP?"

7.4.2. "Why was PGP developed?"

7.4.3. Who developed PGP?

7.5. Importance of PGP

7.5.1. PGP 2.0 arrived at an important time

  • in September 1992, the very same week the Cypherpunks had their first meeting, in Oakland, CA. (Arthur Abraham printed up professional-looking diskette labels for the PGO 2.0 diskettes distributed. A general feeling that we were forming at the "right time.")
  • just 6 months before the Clipper announcement caused a firestorm of interest in public key cryptography

7.5.2. PGP has been the catalyst for major shifts in opinion

  • has educated tens of thousands of users in the nature of strong crypto
  • has led to other tools, including encrypted remailers, experiments in digital money, etc.

7.5.3. "If this stuff is so important, how come not everyone is digitally signing their messages?"

  • (Me, for example. I never sign my messages, and this FAQ is not signed. Maybe I will, later.)
    • convenience, ease of use, "all crypto is economics"
    • insecurity of host Unix machines (illusory)
    • better integration with mailers needed

7.5.4. Ripem appears to be dead; traffic in is almost zero. PGP has obviously won the hearts and minds of the user community; and now that it's "legal"...

7.6. PGP Versions

7.6.1. PGP Versions and Implementations

  • 2.6ui is the version compatible with 2.3
  • What is the difference between versions 2.6 and 2.6ui?
  • "PGP 2.6 is distributed from MIT and is legally available to US and Canadian residents. It uses the RSAREF library. It has code that will prevent interoperation with earlier versions of PGP. "PGP 2.6ui is a modified version of PGP 2.3a which functions almost identically to MIT PGP 2.6, without the "cripple code" of MIT PGP 2.6. It is legally available outside the US and Canada only." [Rat,, 1994-07-03]
    • DOS
      • Versions
      • Pretty Good Shell
  • "When your Microsoft Mail supports an external Editor, you might want to try PGS (Pretty Good Shell), available as PGS099B.ZIP at several ftp sites. It enables you to run PGP from a shell, with a easy way to edit/encrypt files." [HHM LIMPENS, 1994-07-01]
    • Windows
    • Sun
  • "I guess that you should be able to use PGPsendmail, available at' [ (Eric Veldhuyzen), PGP support for Sun's Mailtool?,, 1994-06-29]
  • Mark Grant has been working on a tool to replace Sun's mailtool. "Privtool ("Privacy Tool") is intended to be a PGP-aware replacement for the standard Sun Workstation mailtool program, with a similar user interface and automagick support for PGP-signing and PGP- encryption." [MG, 1994-07-03]
  • "At the moment, the Beta release is available from in /pub/privtool as privtool-0.80.tar.Z, and I've attached the README.1ST file so that you can check out the features and bugs before you download it. ... Currently the program requires the Xview toolkit to build, and has only been compiled on SunOS 4.1 and Solaris 2.1."
    • MacPGP
  • 2.6ui: reports of problems, bombs (remove Preferencs set by previous versions from System folder)
  • "MacPGP 2.6ui is fully compatible with MIT's MacPGP 2.6, but offers several advantages, a chief one being that MacPGP 2.6ui is controllable via AppleScript. This is a very powerful feature, and pre-written AppleScripts are already available. A set of AppleScripts called the Interim Macintosh PGP Interface (IMPI) support encryption, decryption, and signing of files via drag-n- drop, finder selection, the clipboard, all accessible from a system-wide menu. Eudora AppleScripts also exist to interface MacPGP with the mail program Eudora. "MacPGP 2.6ui v1.2 is available via anonymous ftp from: FTP SITE DIRECTORY CONTENTS pub/crypto/macintosh/MacPGP MacPGP 2.6ui, source AppleScripts for 2.6ui are available for U.S. and Canadian citizens ONLY via anonymous ftp from: FTP SITE CONTENTS mpj IMPI & Eudora scripts MacPGP 2.6ui, source [phinely@uhunix.uhcc.Hawaii.Edu (Peter Hinely),, 1994-06-28]
    • Amiga
    • VMS
      • 2.6ui is said to compile and run under VMS.
    • German version
      • MaaPGP0,1T1,1
      • dtp8//dtp,dapmqtadt,gmd,de/ilaomilg/MaaP
      • Ahpiqtoph_Pagalies@hh2.maus.
  • (source: (A.Elbert). by way of (-=Xenon=-), 3-31-94

7.6.2. What versions of PGP exist?

  • PGP 2.7 is ViaCrypt's commercial version of PGP 2.6

7.6.3. PGP 2.6 issues

  • There has been much confusion, in the press and in discussion groups, about the issues surrounding 2.5, 2.6, 2.6ui, and various versions of these. Motivations, conspiracies, etc., have all been discussed. I'm not involved as others on our list are, so I'm often confused too.
  • Here are some comments by Phil Zimmermann, in response to a misleading press report:
  • "PGP 2.6 will always be able to read messages, signatures, and keys from olderversions, even after September 1st. The older versions will not be able to read messages, signatures and keys produced by PGP 2.6 after September 1st. This is an entirely different situation. There is every reason for people to switch to PGP 2.6, because it will be able to handle both data formats, while the older versions will not. Until September, the new PGP will continue to produce the old format that can be read by older versions, but will start producing the new format after that date. This delay allows time for everyone to obtain the new version of PGP, so that they will not be affected by the change. Key servers will still be able to carry the keys made in the old format, because PGP 2.6 will still read them with no problems. " [Phil Zimmermann, 1994-07-07, also posted to Usenet groups] [all dates here refer to 1994]
  • "I developed PGP 2.6 to be released by MIT, and I think this new arrangement is a breakthrough in the legal status of PGP, of benefit to all PGP users. I urge all PGP users to switch to PGP 2.6, and abandon earlier versions. The widespread replacement of the old versions with this new version of PGP fits in with future plans for the creation of a PGP standard." [Phil Zimmermann, 1994-07-07, also posted to Usenet groups]

7.6.4. PGP version 2.6.1

  • "MIT will be releasing Pretty Good Privacy (PGP) version 2.6.1 real soon now. By tomorrow, I think. The MSDOS release filename will be, and the source code will be in The MIT FTP site is net-, in the pub/PGP directory." [corrected by Derek Atkins to be:, not net-] "This new version has a lot of bug fixes over version 2.6. I hope this is the final release of this family of PGP source code. We've been working on an entirely new version of PGP, rewritten from scratch, which is much cleaner and faster, and better suited for the future enhancements we have planned. All PGP development efforts will be redirected toward this new code base, after this 2.6.1 release." [Phil Zimmermann, Cypherpunks list, 1994-09-02]

7.7. Where to Get PGP?

7.7.1. "Where can I get PGP on CompuServe?"

  • Note: I can't keep track of the major ftp sites for the various crypto packages, let alone info on services like this. But, here it is;
    • "Current as of 5-Jul-1994:" GO EURFORUM / Utilities...PGP26UI.ZIP...PGP 2.6ui GO PWOFORUM / New uploads PGP26.ZIP...PGP 2.6 PWOFORUM also has the source code and documentation, plus a number of shell utilities for PGP. Version 2.3a is also still around." [, Kevin Martin, PGP on Compuserve??,, 1994-07-08]

7.7.2. Off line PGP

  • ftp.informatik.uni-
  • another place: Crosspoint: ftp.uni- XP302*.EXE
  • "I highly recommend Offline AutoPGP v2.10. It works seamlessly with virtually any offline mail reader that supports .QWK packets. Shareware registration is $10.00 US. The author is Staale Schumacher, a student at the University of Oslo, is reachable at . The program should be pretty widely available on US bbs's by now. I use the program constantly for bbs mail. It's really quite a slick piece of work. If you have any trouble finding it, drop me a note." [ Brent H. Howatt, PGP in an offline reader?,, 1994-07-05]
    • in /pub/msdos/offline, version 2.11
  • ftp.informatik.uni-

7.7.3. "Should I worry about obtaining and compiling the PGP sources?"

  • Well, unless you're an expert on the internals of PGP, why bother? And a subtle bug in the random number generator eluded even Colin Plumb for a while.
  • The value of the source being available is that others can, if they wish, make the confirmation that the executable correspond to the source. That this can be done is enough for me. (Strategy: Hold on to the code for a while, wait for reports of flaws or holes, then use with confidence.)
  • Signatures can be checked. Maybe timestamped versions, someday.
  • Frankly, the odds are much higher that one's messages or pseudonymous identity will be exposed in others ways than that PGP has been compromised. Slip-ups in sending messages sometimes reveal identities, as do inadvertent comments and stylistic cues.

7.8. How to Use PGP

7.8.1. How does PGP work?

7.8.2. "How should I store the secret part of my key? Can I memorize it?"

  • Modern ciphers use keys that are far beyond memorization (or even typing in!). The key is usually stored on one's home machine, or a machine that is reasonably secure, or on diskette. The passphrase should always be memorized or written down (ugh) in one's wallet or other such place. Secure "dongles" worn around the neck, or a ring or watch, may eventually be used. Smartcards and PDAs are a more likely intermediate solution (many PCs now have PCMCIA card slots).

7.8.3. "How do I sign messages?"

  • cf. the PGP docs
  • however, this has come up on the List, and:
    • pgp -sta +clearsig=on message.txt
  • That's from pgpdoc2.txt. Hope it helps. You might wish to set up your mail
  • user agent to invoke this command upon exiting your default message editor,
  • with "message.txt" set to whatever your editor calls the temporary message
  • file. <Russell Whitaker,, 4-15-94, Cypherpunks>

7.8.4. Why isn't PGP easier to use?

  • Compared to other possible crypto applications (like digital money or voting systems), it is actually very easy to use
    • semantic gap...learning

7.8.5. How should I learn PGP?

7.8.6. "What's the status of PGP integration with other programs?"

  • Editors
    • emacs
  • emacs supports pgp, probably in various flavors (I've seen several reports of different packages)..the built- in language certainly helps
  • Rick Busdiecker has an emacs front end to PGP available
  • Jin S. Choi jsc@monolith.MIT.EDU once described a package he wrote in elisp which supported GNU emacs: "mailcrypt"
  • there are probably many more
    • Mailers
  • That is, are there any mailers that have a good link to PGP? Hooks into existing mailers are needed
    • emacs
  • emacs supports pgp, probably in various flavors (I've seen several reports of different packages)..the built- in language certainly helps
  • Rick Busdiecker has an emacs front end to PGP available
  • Jin S. Choi jsc@monolith.MIT.EDU once described a package he wrote in elisp which supported GNU emacs: "mailcrypt"
  • there are probably many more
    • elm
    • Eudora
    • PGP sendmail, etc.
    • "Get the PGPsendmail Suite, announced here a few days ago. It's available for anonymous ftp from: pub/people/rgooch (Australia) pub/crypto/pgp/PGPsendmail(U.S.A.) src/security (U.K.)... It works by wrapping around the regular sendmail programme, so you get automatic encryption for all mailers, not just Rmail. " [Richard Gooch,, 1994-07-10] + MIME
  • MIME and PGP <Derek Atkins, 4-6-94>
  • [the following material taken from an announcement forwarded to the Cypherpunks list by, 1994-07-05]
  • "MIME [RFC-1341, RFC-1521] defines a format and general framework for the representation of a wide variety of data types in Internet mail. This document defines one particular type of MIME data, the application/pgp type, for "pretty good" privacy, authentication, and encryption in Internet mail. The application/pgp MIME type is intended to facilitate the wider interoperation of private mail across a wide variety of hardware and software platforms.
    • Newsreaders
  • useful for automatic signing/verification, and e-mail from withing newsreader
    • yarn
    • tin
    • The "yarn" newsreader reportedly has PGP built in.

7.8.7. "How often should I change my key or keys?"

  • Hal Finney points out that many people seem to think PGP keys are quasi-permanent. In fact, never changing one's key is an invitation to disaster, as keys may be compromised in various ways (keystroke capture programs, diskettes left lying around, even rf monitoring) and may conceivably be cracked.
  • "What is a good interval for key changes? I would suggest every year or so
  • makes sense, especially if infrastructure can be developed to make it easier
    • to propagate key changes. Keys should be overlapped in time, so that you make
  • a new key and start using it, while continuing to support the old key for a
  • time. <Hal Finney,, 4-15-94, cypherpunks>
  • Hal also recommends that remailer sites change their keys even more frequently, perhaps monthly.

7.9. Keys, Key Signings, and Key Servers

7.9.1. Web of trust vs. heierarchical key management

  • A key innovations of Phil Zimmermann was the use of a "web of trust" model for distributed trust in keys.
    • locality, users bear costs
  • by contrast, government estimates $1-2 B a year to run key certification agencies for a large fraction of the population
  • "PGP is about choice and constructing a web of trust that suits your needs. PGP supports a completely decentralized, personalized web of trust and also the most highly structured bureaucratic centralized scheme you could imagine. One problem with relying solely on a personalized web of trust is that it limitsyour universe of correspondents. We can't expect Phil Zimmermann and a few well-known others to sign everyone's key, and I would not want to limit my private correspondence to just those people I know and trust plus those people whose keys have been signed by someone I know and trust." [William Stallings, SLED key verification,, 1994-0901]

7.9.2. Practical approaches to signing the keys of others

  • sign keys of folks you know and wish to communicate with
    • face-to-face encounters ("Here is my key.")
  • trust--to varying extents--the keys signed by others you know
    • web-of-trust
  • trust--to a lesser extent--the keys of people in key registries

7.9.3. Key Servers

  • There are several major sites which appear to be stable
    • MIT PGP Public Key Server
      • via
  • Vesselin Bontchev at University of Hamburg operates a very stable one: - Ftp: IP:... Dir:.../pub/virus/crypt/pgp/ File:...pubkring.pgp E-Mail:
  • This is a PGP keyserver in Zurich. <Russell Whitaker, 7 April 1994>

7.9.4. Use of PGP key fingerprints

  • "One of the better uses for key fingerprints is for inclusion in signature files and other places that a key itself is too bulky. By widespread dissemination of the fingerprint, the chances of a bogus key being undetected are decreased, since there are more channels for the fingerprint to get to recipients, and more channels for the owner of a key to see any bogus fingerprints out on the net. [Bill Stewart, 1994-08-31]

7.9.5. "How should address changes be handled? Do old keys have to be revoked?"

  • Future versions of PGP may handle better
  • One way is to issue ... "User-id revocation certificates are a good idea and the PGP key format allows for them - maybe one day PGP will do something about it." [Paul Allen,, 1994-07-01]
  • Persistent e-mail addresses is one approach. Some people are using organization like the ACM to provide this (e.g., Phil Zimmermann is Others are using remapping services. For example, "I signed up with the SLED (Stable Large E-mail Database), which is a cross-referencing database for linking old, obsolete E-mail addresses with current ones over the course of time... Anyone using this key will always be able to find me on the SLED by conducting a search with "blbrooks..." as the keyword. Thus my key and associated sigs always remain good... If you are interested in the SLED, its address is" [Robert Brooks,, 1994-0701]

7.9.6. "How can I ensure that my keys have not been tampered with?" + Keep your private key secure

+ if on an unsecured machine, take steps to protect it
  • offlline storage (Perry Metzger loads his key(s) every morning, and removes it when he leaves the machine)
  • memorize your PGP passphrase and don't write it down, at least not anywhere near where the private key is available
  • sealed envelopes with a lawyer, safe deposit boxes, etc., are possibilities
  • given the near-impossibility of recovering one's files if the passphrase is lost permanently, I recommend storing it someplace, despite the slight loss in security (this is a topic of debate...I personally feel a lot more comfortable knowing my memory is backed up somewhere)
  • Colin Plumb has noted that if someone has accesss to your personal keyring, they also probably have access to your PGP program and could make modifications to it directly.
  • Derek Atkins answered a similar question on sci.crypt: "Sure. You can use PGP to verify your keyring, and using the web-of-trust, you can then have it verify your signatures all the keys that you signed, and recurse through your circle-of-friends....To verify that your own key was not munged, you can sign something with your secret key and then try to verify it. This will ensure that your public key wasn't munged." [Derek Atkins, sci.crypt, 199407-06]

7.9.7. "Why are key revocations needed?"

  • Key revocation is the "ebb-of-trust"
  • "There are a number of real reasons. Maybe you got coerced into signing the key, or you think that maybe the key was signed incorrectly, or maybe that person no longer uses that email address, because they lost the account, or that maybe you don't believe that the binding of key to userID is valid for any number of reasons." [Derek Atkins, 4-2894]

7.9.8. "Is-a-person" registries

  • There have been proposals that governments could and should create registries of "legal persons." This is known in the crypto community as "is-a-person" credentialling, and various papers (notably Fiat-Shamir) have dealt with issues
    • of spoofing by malicious governments
    • of the dangers of person-tracking
    • We need to be very careful here!
      • this could limit the spread of 'ad hoc crypto' (by which I mean the use of locally-generated keys for reasons other than personal cash, pseudonyms etc.)
  • any system which "issues" permission slips to allow keys to be generated is dangerous!
    • Could be an area that governments want to get into.
  • a la Fiat-Shamir "passport" issues (Murdoch, Libyan example)
  • I favor free markets--no limitations on which registries I can use

7.9.9. Keyservers (this list is constantly changing, but most share keys, so all one needs is one). Send "help" message. For current information, follow

  • about 6000 keys on the main keyservers, as of 1994-08.
  • and offers public keys by finger (I couldn't get it to work)

7.9.10. "What are key fingerprints and why are they used?"

  • "Distributing the key fingerprint allows J. Random Human to correlate a key supplied via one method with that supplied via another. For example, now that I have the fingerprint for the Betsi key, I can verify whether any other alleged Betsi key I see is real or not...It's a lot easier to read off & cross-check 32-character fingerprints than the entire key block, especially as signatures are added and the key block grows in size." [Paul Robichaux, 1994-08-29]

7.9.11. Betsi

  • Bellcore
  • key signing

7.9.12. on attacks on keyservers...

  • flooding attacks on the keyservers have started; this may be an attempt to have the keyservers shut down by using obscene, racist, sexist phrases as key names (Cypherpunks would not support shutting down a site for something so trivial as abusive, offensive language, but many others would.)
  • "It appears that some childish jerk has had a great time generating bogus PGP keys and uploading them to the public keyservers. Here are some of the keys I found on a keyserver:...[keys elided]..." [,, 1994-09-05]

7.10. PGP Front Ends, Shells, and Tools

7.10.1. Many can be found at this ftp site:

    • for various shells and front-ends for PGP

7.10.2. William Stallings had this to say in a Usenet post:

  • "PGPShell: runs directly on the DOS version, doesn't need Windows. Nice, simple interface. freeware "PGP Winfront: freeware windows front end. Uses a "control panel" style, with many options displayed in a compact fashion. "WinPGP: shareware ($45). Uses a drop-down menu style, common to many Windows applications." [William Stallings, Looking for PGP front end,, 1994-08-31]

7.10.3. Rick Busdiecker has an emacs front end to PGP available

7.10.4. Pr0duct Cypher's tools:

  • ftp.informatik.uni-
    • Pr0duct Cypher's tools, and other tools in general

7.11. Other Crypto Programs And Tools

7.11.1. Other Ciphers and Tools

  • PEM
  • MD5
  • SFS (Secure FileSystem) 1.0
  • "SFS (Secure FileSystem) is a set of programs which create and manage a number of encrypted disk volumes, and runs under both DOS and Windows. Each volume appears as a normal DOS drive, but all data stored on it is encryped at the individual-sector level...SFS 1.1 is a maintenance release which fixes a few minor problems in
  1. 0, and adds a number of features suggested by users. More details on changes are given in in the README file." [Peter Gutmann, sci.crypt, 1994-08-25]
    • not the same thing as CFS!
    • 512-bit key using a MDC/SHS hash. (Fast)
    • only works on a386 or better (says V. Bontchev)
    • source code not available?
    • implemented as a device driver (rather than a TSR, like SecureDrive)
  • "is vulnerable to a special form of attack, which was mentioned once here in sci.crypt and is described in detaills in the SFS documentation. Take a loot at the section "Encryption Considerations"." [Vesselin Bontchev, sci.crypt, 1994-07-01]
  • Comparing SFS to SecureDrive: "Both packages are approximately equal in terms of user interface, but SFS seems to be quite a bit faster. And comments from various people (previous message thread) seems to indicate that it is more "secure" as well." [Bill Couture , sci.crypt, 1994-0703]
    • SecureDrive
      • encrypts a disk (always be very careful!)
  • SecureDrive 1.3D, 128-bit IDEA cypher is based on an MD5 hash of the passphrase
  • implemented as a TSR (rather than a device driver, like CFS)
    • source code available
    • Some problems reported (your mileage may vary)
  • "I have been having quite a bit of difficulty with my encrypted drive mangling files. After getting secure drive 1.3d installed on my hard drive, I find that various files are being corrupted and many times after accessing the drive a bunch of crosslinked files are present." [, 1994-07-01]
  • Others report being happy with, under both DOS and Windows
  • no OS/2 or Mac versions reported; some say an OS/2 device driver will have to be used (such as Stacker for OS/2 uses)
    • SecureDevice
  • "If you can't find it elsewhere, I have it at, but that's at the end of a saturated 64kbps link." [Alan Barrett, 1994-07-01]

7.11.2. MDC and SHS (same as SHA?)

  • "The MDC cyphers are believed to be as strong as it is difficult to invert the cryptographic hash function they are using. SHS was designed by the NSA and is believed to be secure. There might be other ways to attack the MDC cyphers, but nobody who is allowed to speak knows such methods." [Vesselin Bontchev, sci.crypt, 1994-07-01]
  • Secure Hash Standard's algorithm is public, and hence can be analyzed and tested for weaknesses (in strong contrast with Skipjack).
    • may replace MD5 in future versions of PGP (a rumor)
  • Speed of MDC: "It's a speed tradeoff. MDC is a few times faster than IDEA, so SFS is a few times faster than SecureDrive. But MDC is less proven." [Colin Plumb, sci.crypt, 1994-07-04]
    • Rumors of problems with SHA
  • "The other big news is a security problem with the Secure Hash Algorithm (SHA), discussed in the Apr 94 DDJ. The cryptographers at NSA have found a problem with the algorithm. They won't tell anyone what it is, or even how serious it is, but they promise a fix soon. Everyone is waiting with baited breath." [Bruce Schneier, reprot on Eurocrypt '94, 1994-07-01]

7.11.3. Stego programs

  • DOS
  • S-Tools (or Stools?). DOS? Encrypts in .gif and .wav (SoundBlaster format) files. Can set to not indicate encrypted files are inside.
    • Windows
    • Macintosh
      • Stego
      • sound programs
  • marielsn@Hawaii.Edu (Nathan Mariels) has written a program which "takes a file and encrypts it with IDEA using a MD5 hash of the password typed in by the user. It then stores the file in the lowest bit (or bits, user selectable) of a sound file."

7.11.4. "What about "Pretty Good Voice Privacy" or "Voice PGP" and Other Speech Programs?"

  • Several groups, including one led by Phil Zimmermann, are said to be working on something like this. Most are using commercially- and widely-available sound input boards, a la "SoundBlaster" boards.
  • proprietary hardware or DSPs is often a lose, as people won't be able to easily acquire the hardware; a software- only solution (possibly relying on built-in hardware, or readily-available add-in boards, like SoundBlasters) is preferable.
    • Many important reasons to do such a project:
      • proliferate more crypto tools and systems
      • get it out ahead of "Digital Telephony II" and Clipper type systems; make the tools so ubiquitous that outlawing them is too difficult
  • people understand voice communcations in a more natural way than e-,mail, so people who don't use PGP may nevertheless use a voice encryption system
  • Eric Blossom has his own effort, and has demonstrated hardware at Cypherpunks meetings:
  • "At this moment our primary efforts are on developing a family of extensible protocols for both encryption and voice across point to point links. We indend to use existing standards where ever possible. "We are currently planning on building on top of the RFCs for PPP (see RFCs 1549, 1548, and 1334). The basic idea is to add a new Link Control Protocol (or possibly a Network Control Protocol) that will negotiate base and modulus and perform DH key exchange. Some forms of Authentication are already supported by RFCs. We're looking at others." [Eric Blossom, 1994-04-14]
  • Building on top of multimedia capabilities of Macintoshes and Windows may be an easier approach
  • nearly all Macs and Windows machines will be multimedia/audiovisual-capable soon
  • "I realize that it is quite possible to design a secure phone with a Vocoder, a modem and some cpu power to do the encryption, but I think that an easier solution may be on the horizon. ...I believe that Microsoft and many others are exploring hooking phones to PCs so people can do things like ship pictures of their weekend fun to friends. When PC's can easily access phone communications, then developing encrypted conversations should be as easy as programming for Windows :-)." [Peter Wayner, 1993--07-08]

7.11.5. Random Number Generators

  • A huge area...
  • Chaotic systems, pendula
  • may be unexpected periodicities (phase space maps show basins of attraction, even though behavior is seemingly random)

7.11.6. "What's the situation on the dispute between NIST and RSADSI over the DSS?"

  • NIST claims it doesn't infringe patents
  • RSADSI bought the Schnorr patent and claims DSS infringes it
  • NIST makes no guarantees, nor does it indemnify users [Reginald Braithwaite-Lee, talk.politics.crypto, 1994-0704]

7.11.7. "Are there any programs like telnet or "talk" that use pgp?" - "Don't know about Telnet, but I'd like to see "talk"

secured like that... It exists. (PGP-ized ytalk, that is.) Have a look at ftp.informatik.uni-" [Vesselin Bontchev,, 1994-07-4]

7.11.8. Digital Timestamping

  • There are two flavors:
    • toy or play versions
    • real or comercial version(s)
  • For a play version, send a message to "" and it will be timestamped and returned. Clearly this is not proof of much, has not been tested in court, and relies solely on the reputation of the timestamper. (A fatal flaw: is trivial to reset system clocks on computes and thereby alter dates.)
  • "hearsay" equivalent: time stamps by servers that are not using the "widely witnessed event" approach of Haber and Stornetta
  • The version of Haber and Stornetta is of course much more impressive, as it relies on something more powerful than mere trust that they have set the system clocks on their computers correctly!

7.12.1. "What is RSA Data Security Inc.'s position on PGP?"

I. They were strongly opposed to early versions II. objections

  • infringes on PKP patents (claimed infringements, not tested in court, though)
    • breaks the tight control previously seen
  • brings unwanted attention to public key approaches (I think PGP also helped RSA and RSADSI)
    • bad blood between Zimmermann and Bidzos III. objections
  • infringes on PKP patents (claimed infringements, not tested in court, though)
    • breaks the tight control previously seen
  • brings unwanted attention to public key approaches (I think PGP also helped RSA and RSADSI)
    • bad blood between Zimmermann and Bidzos IV. Talk of lawsuits, actions, etc. V. The 2.6 MIT accomodation may have lessened the tension; purely speculative

7.12.2. "Is PGP legal or illegal"?

7.12.3. "Is there still a conflict between RSADSI and PRZ?"

  • Apparently not. The MIT 2.6 negotiations seem to have buried all such rancor. At least officially. I hear there's still animosity, but it's no longer at the surface. (And RSADSI is now facing lawsuits and patent suits.)

7.13. Problems with PGP, Flaws, Etc.

7.13.1. Speculations on possible attacks on PGP

  • There are periodically reports of problems, most just rumors. These are swatted-down by more knowledgeable people, for the most part. True flaws may exist, of course, as in any piece of software.
  • Colin Plumb acknowledged a flaw in the random number generation process in PGP 2.6, to be fixed in later versions.
    • spreading fear, uncertainty and doubt
      • rumors about security of PGP versions
      • selective prosecution of PGP users
      • death threats (a la against Bidzos)
    • sowing confusion in the user community
  • fragmenting it (perhaps via multiple, noninteroperable versions...such as we're beginning to see now?)

7.13.2. What does the NSA know about flaws in PGP?

  • They're not saying. Ironically, this violates the part of their charter that deals with making commercial security stronger. Now that PGP is kosher, they should help to make it stronger, and certainly should not keep mum about weaknesses they know about. But for them to help strengthen PGP is not really too likely.

7.13.3. The PGP timebomb

  • (As I've said elsewhere, it all gets very confusing. Many versions, many sites, many viewpoints, many tools, many shells, many other things. Fortunately, most of it is flotsam.)
  • I take no point of view--for various reasons--on avoiding the "timebomb" by using 2.6ui. Here's someone else's comment: "I would like to take this time to encourage you to upgrade to 2.6ui which will overcome mit's timebomb and not exclude PGP 2.3a from decrypting messages...DON'T USE MIT's 2.6, use PGP 2.6ui available from : /pub/cypherpunks/pgp" [Matrix at Cypherpunks, BLACK THURSAY!,, 1994-09-01]
    • can also be defeated with the "legal kludge":
  • : /pub/virus/crypt/pgp/legal_kludge.txt

7.13.4. Spoofing

  • "Suitable timing constraints, and in particular real-time constraints, can be used to hinder, and perhaps defeat, spoofing attacks. But with a store-and-forward e-mail system (such as PGP is designed to work with) these constraints cannot, in general, be set." [Ken Pizzini , sci.crypt, 1994-07-05]

7.13.5. "How do we know that PGP doesn't have a back door or some other major flaw? After all, not all of us are programmers or cryptologists."

  • Yes, but many of us are. Many folks have analyzed the source code in PGP, have compiled the code themselves (a fairly common way to get the executable), and have examined the random number generators, the selection of primes, and all of the other math.
  • It would take only a single sharp-eyed person to blow the whistle on a conspiracy to insert flaws or backdoors. This has not been done. (Though Colin Plumb ackknowledged a slight weakness in the RNG of 2.6...being fixed.)
  • "While having source code available doesn't guarantee that the program is secure, it helps a lot. Even though many users are not programmers or cryptographers, others are, and many of these will examine the code carefully and publicly yell about weaknesses that they notice or think they notice. For example, apparently there was a big discussion here about the xorbytes() bug in PGP 2.6. Contrast this with a commercial program, where such a bug might go undetected for years." [Paul Rubin,, 1994-09-06]

7.13.6. "Can I run PGP on a machine I don't control, e.g., the campus computer system?"

  • Sure, but the sysops and others may then have access to your key and passphrase. Only machines the user directly controls, and that are adequately firewalled from other machines, offer reasonable amounts of security. Arguing about whether 1024-bit keylengths are "enough" is rather moot if the PGP program is being run on a corportate computer, or a university network. The illusion of security may be present, but no real security. Too many people are kidding themselves that their messages are secure. That their electronic identities cannot be spoofed.
  • I'm not interested in the various elm and emacs PGP packages (several such shells and wrappers exist). Any sysop can not only obtain your secret key, stored on hissystem, but he can also capture your passphrase as you feed it to the PGP program (assuming you do...many people automate this part as well). Since this sysop or one of his cronies can then compromise your mail, sign messages and contracts as "you," I consider this totally unacceptable. Others apparently don't.
  • What can be done? Many of us only run PGP on home machines, or on machines we directly control. Some folks who use PGP on such machines at least take steps to better secure things...Perry Metzger, for example, once described the multi-stage process he went through each day to reload his key material in a way he felt was quasi-safe.
  • Until the "Internet-in-a-box" or TIA-type products are more widespread, many people will be connecting home or office machines to other systems they don't control. (To put this in sharper focus: do you want your electronic money being run out of an account that your sysop and his friends can monitor? Not hardly. "Electronic purses," which may be smart cards, Newton-like PDAs, or dongle-like rings or pendants, are clearly needed. Another entire discussion.)

7.14. The Future of PGP

7.14.1. "Does PGP help or hurt public key methods in general and RSA Data Security Inc. in particular?"

  • The outcome is not final, but on balance I think the position of RSADSI is helped by the publicity PGP has generated. Users of PGP will "graduate" to fully-licensed versions, in many cases. Corporations will then use RSADSI's products.
  • Interestingly, PGP could do the "radical" things that RSADSI was not prepared to do. (Uses familiar to Cypherpunks.)
    • bypassing export restrictions is an example of this
    • incorporation into experimental digital cash systems
  • Parasitism often increases the rate of evolution. Certainly PGP has helped to light a fire under RSADSI.

7.14.2. Stealth PGP

  • Xenon, Nik, S-Tools,

7.14.3. "Should we work on a more advanced version, a Really Good Privacy?"

  • easier said than done...strong committment of time
  • not clear what is needed...

7.14.4. "Can changes and improvements be made to PGP?"

  • I consider it one of the supreme ironies of our age that Phil Zimmermann has denounced Tom Rollins for making various changes to a version of PGP he makes available.
    • Issues:
      • Phil's reputation, and that of PGP
      • intellectual property
      • GNU Public license
      • the mere name of PGP
  • Consider that RSA said much the same thing, that PGP would degrade the reputation of public key (esp. as Phil was an "amateur," the same exact phrasing PRZ uses to criticize Tom Rollins!)
    • I'm not taking a stand here...I don't know the details. Just some irony.

7.15. Loose Ends

7.15.1. Security measures on login, passwords, etc.

  • Avoid entering passwords over the Net (such as in rlogins or telnets). If someone or some agent asks for your password, be paranoid.
  • Can use encrypted telnet, or something like Kerberos, to avoid sending passwords in the clear between machines. Lots of approaches, almost none of them commonly used (at least I never see them).