Pretty Good Privacy version 2.6.3i - READ ME FIRST

Notes by Stale Schumacher, 1996/01/18

You are looking at the README file for PGP release 2.6.3i. PGP, short for Pretty Good Privacy, is a public key encryption package; with it, you can secure messages you transmit against unauthorized reading and digitally sign them so that people receiving them can be sure they come from you.

About this version

PGP 2.6.3i is not an official PGP version. It is based on the source code for MIT PGP 2.6.2 (the latest official version of PGP) and has been modified for international use. PGP 2.6.3i is probably illegal to use within the USA, but is fine in almost every other country in the world. (However, it should be possible to compile a version of PGP that is legal even inside the USA, see below for details.) This file only explains what is special to version 2.6.3i. For a more thorough installation and usage guide, refer to the file setup.doc and the documentation for PGP 2.6.2, which is included unmodified in the doc/ subdirectory that is created when you unpack the distribution archive.


Until about two years ago, there were only two "real" PGP versions around: PGP 2.3a which was the international freeware version, and 2.4 which was a commercial version sold in USA only. However, this situation changed dramatically in May 1994 when MIT released a special US freeware version of PGP (2.5), in order to put an end to the legal problems surrounding PGP. (PGP 2.3a was believed to be illegal in USA because of patent restrictions.) The new version had a number of limitations to encourage Americans that were using 2.3a to upgrade to the new version. However, these limitations resulted in a well of new PGP versions, more or less professionally put together by well-intending individuals who wanted a more flexible PGP than that offered by MIT. Suddenly, we had ten different PGP versions, not two.

Even though PGP 2.5 and later releases from MIT introduced many bug-fixes and improvements over 2.3a, many non-US users of PGP have been reluctant to upgrade to the new versions because they feel that the PGP developers have abandoned the international PGP community by adding a number of restrictions that are only necessary within the USA. That is why I decided to make PGP 2.6.i (and later 2.6.2i and 2.6.3i): to put an end to all the PGP "hack versions" that flourish, and by giving the non-US users of PGP a version that is more "digestible" than those offered by MIT, and at the same time let them benefit from all the improvements that the new versions have introduced over PGP 2.3a. PGP 2.6.3i is a "real" 2.6 version, as it is based on the code tree for PGP 2.6.2 and not 2.3a. This release fixes a number of bugs present in PGP 2.6.2(i), and adds some new features (see below).

How was it done?

PGP 2.6.3i was put together by taking all the source files from PGP 2.6.2i (which was again based on 2.6.2), modifying them to correct a number of annoying bugs and add some new features, and updating the accompanying text and documentation files. All changes in the source that are not applicable within the USA are enclosed in #ifdef's, thus enabling you to compile a PGP version that is legal to use within the USA. This is accomplished by adding the -DUSA option when building the program, and by linking it with the RSAREF library (rsaglue2) rather than MPILIB (rsaglue1). For a detailed list of all the changes between 2.6.2i and 2.6.3i, see the file pgp263i.dif that is included with the source code distribution.


PGP 2.6.3i is distributed in the following files:
This is the MS-DOS executable release, which includes the executable, support files, and basic documentation.
This is a 32-bit MS-DOS compilation of PGP. If you have a 386 processor or better, this version will give you a slightly better performance than the ordinary (16-bit) MS-DOS version. (
This is the OS/2 executable with documentation and support files.
This is the source code release, which includes all the source code needed to compile PGP and examples of usage. It also contains all the files in except the pgp.exe binary.
This contains exactly the same files as, except that they use Unix rather than MS-DOS line end conventions.
Binaries for other platforms (Amiga, Atari, Macintosh etc.) will probably be available soon after the official release.

Differences between PGP 2.6.3i and 2.6.2

PGP 2.6.3i differs from MIT PGP 2.6.2 in the following ways:
  1. It identifies itself as version 2.6.3i

    This is to clearly distinguish it from other PGP versions. This is important because users within the USA should not use PGP 2.6.3i, and also because script files, shells and other PGP add-ons may need to know exactly how your copy of PGP will behave under different circumstances. If you compile your copy of PGP using the -DUSA option, you will get a version called 2.6.3 instead.

  2. It uses PRZ's MPILIB instead of RSAREF

    PGP 2.3a and earlier versions use a special library for all the RSA encryption/decryption routines, called MPILIB, and written by Philip R. Zimmermann (PRZ), the original author of PGP. However, starting with version 2.5, all official releases of PGP have been using the RSAREF library from RSADSI Inc, a US company that holds the patent on the RSA algorithm in the USA. This change was made in order to make PGP legal to use within the USA.

    Please observe that PGP 2.6.3i does NOT use RSAREF, but rather PRZ's original MPILIB library, which is functionally identical to RSAREF and slightly faster on most platforms. Because 2.6.3i uses MPILIB rather than RSAREF, this PGP version is also able to verify key signatures made with PGP 2.2 or earlier versions. This is not true for MIT PGP, because the RSAREF library only understands the new PKCS signature format introduced in PGP 2.3.

    The use of the MPILIB library is the main reason why PGP 2.6.3i is probably illegal to use within the USA. If you are in the USA, you should compile the source code using the -DUSA option and link it with the RSAREF library rather than MPILIB.

  3. It lets you disable the "legal kludge"

    PGP 2.6.2 contains a "feature" that will cause it to generate keys and messages that are not readable by PGP 2.3a and earlier versions. This is the "legal kludge", and was introduced to encourage users in the USA to upgrade from PGP 2.3a.

    PGP 2.6.3i provides you with a way to disable the "legal kludge". This means that messages and keys generated with PGP 2.6.3i can be used and understood by all existing 2.x versions of PGP. To disable the legal kludge, uncomment the following line in your config.txt file so that it reads:

          legal_kludge = off
    This option may also be set on the command line: "pgp +le=off ". If you compile PGP using the -DUSA option, the legal kludge cannot be disabled.
  4. It allows you to generate keys up to and including 2048 bits

    Because of a bug in PGP 2.6.2, this version would not let you generate keys bigger than 2047 bits on some platforms. This problem has been corrected in PGP 2.6.3i.

  5. It contains a number of bug-fixes

    PGP 2.6.3i also fixes a number of other bugs found in PGP 2.6.2, most notably the signature bug for keys over 2034 bits, as reported by ViaCrypt. PGP 2.6.3i will also let you clearsign messages in 8-bit character sets, such as Russian, Japanese, Korean etc. Many other bugs have also been corrected, see pgp262i.dif and pgp263i.dif for details.

  6. It contains a number of new features

    Version 2.6.3i adds some new functionality to PGP, while maintaining compatibility with older versions, e.g.:

    1. You may now specify additional user IDs from a separate file when encrypting a message to multiple recipients. This is particularly useful on MS-DOS systems, which impose an upper limit of 127 characters on the command line. The command line syntax is:
               pgp -eat filename.txt user1 user2 -@moreusers.txt
      The file moreusers.txt is a normal text file with one key ID or user ID on each line.
    2. Userids can be automatically signed with your secret key when creating keys ('pgp -kg') or adding new userids ('pgp -ke'). This is controlled through the new AutoSign option in the configuration file.
    3. When extracting keys with the 'pgp -kxa' command, PGP 2.6.3i will label the ASCII output with a text similar to that of the 'pgp -kv' keyring listing.
    4. When clearsigning messages, PGP 2.6.3i will add a "Charset:" header to the signature block, explaining which character set was used for creating the signature. This will help the recipient of the message to select correct character conversion when verifying the signature. If he/she is using version 2.6.3i, PGP will automatically choose the correct character set, thereby eliminating a lot of "Bad signature" problems.
  7. It can be compiled on many new platforms

    PGP 2.6.3i has been modified in order to let it compile "out of the box" for such platforms as Amiga, Atari, VMS, IBM mainframes running MVS and Windows NT/Windows 95. Furthermore, the Macintosh port of PGP is now integrated into the main source distribution. PGP 2.6.3i will also compile under MS-DOS using Borland C (MIT PGP 2.6.2 only supports Microsoft C).

  8. It includes updated documentation and language files

    The language files for MIT PGP 2.6.2 had not been updated for a long time. This has been fixed in this version. PGP 2.6.3i comes with a combined translation file for German, French and Spanish. Additional language modules may be downloaded from:

    All the other text and documentation files for PGP 2.6.3i have also been brought up to date, with the exception of PRZ's original PGP Users's Guide from PGP 2.6.2, which is included unmodified in the various distribution archives.
  9. It includes additional PGP tools

    The PGP 2.6.3i source code distribution contains two new tools for use with PGP, called Stealth and PGPSort. Take a look in the contrib/ subdirectory for details. The binary distributions now contain pre- compiled versions of PGPSort and MD5Sum.

Differences between PGP 2.6.3i and 2.6ui

A PGP version that has been very popular among non-US users of PGP is 2.6ui. If you have been using PGP 2.6ui up to now, you should note that PGP 2.6.3i differs from this version in the following ways:
  1. It is a "real" 2.6 version

    PGP 2.6.3i is based on the source code for PGP 2.6.2, whereas PGP 2.6ui is based on the source code for 2.3a. This means that 2.6.3i contains a lot of bug-fixes that are not present in 2.6ui, and it also adds a number of new features that are lacking in 2.6ui.

  2. It doesn't have the version_byte option

    PGP 2.6ui has an option to allow you to choose which message format to use when generating keys and messages. This is the version_byte option, and can be set both in the config.txt file and on the command line:

          version_byte = 2    (use backwards-compatible format, default)
          version_byte = 3    (use new 2.6 format)
    In PGP 2.6.3i, the same is accomplished using the legal_kludge flag:
          legal_kludge = off  (use backwards-compatible format)
          legal_kludge = on   (use new 2.6 format, default)
  3. It doesn't have the armor_version option

    PGP 2.6ui has an option to let you "forge" the version number in the ASCII armored files produced by PGP. In PGP 2.6.3i, the armor_version option is NOT supported, as this is a feature that is heavily misused. If you must change the version number of your keys and messages, you can do so in the language.txt file instead.

Legal Stuff

PGP 2.6.3i is not approved by MIT or PRZ or NSA or the Pope or anyone else. However, it should be possible to use it legally by anyone in the free world (i.e. all countries except USA, France, Iraq and a few others). There are three reasons why people may claim (incorrectly) that PGP 2.6.3i is illegal:
  1. It is based on source code that was illegally exported from the USA

    The ITAR regulations classifies cryptography in the same category as munitions, and so it is very likely that exporting PGP from the USA is considered illegal by US authorities. In the case of PGP 2.6.3i, large portions of the code were written inside the USA, and later exported to the rest of the world. However, this is not a problem, because it is the _export_ that is illegal, not the _use_ of the program. Once the software is (illegally) exported, anyone may use it legally. (I didn't export it, and I strongly recommend that you won't do it either.) As long as you make sure that you get your copy of PGP 2.6.3i from somewhere outside the USA, then you should be on the safe side.

  2. It infringes the RSA patent

    This is not a problem either, because PGP 2.6.3i is not intended for use in the USA (which just happens to be the only country in the world where the RSA patent is valid, and still the validity of this patent is somewhat dubious). If you are inside the USA, you should compile the source using the -DUSA option and link it with the RSAREF library, which will give you a version that identifies itself as PGP 2.6.3.

  3. It violates the MIT license

    The second point in the MIT license for PGP 2.6.2 explicitly forbids anyone to remove the so-called "legal kludge". Still, this is exactly what PGP 2.6.3i does. However, it should be clear that this limitation only refers to the RSAREF versions of PGP. PGP 2.6.3i, on the other hand, does not use RSAREF, and so this point becomes irrelevant. If you still feel uncomfortable about this, take a look at the file przon26i.asc which is included in the distribution archive. This file contains a statement by Phil Zimmermann on PGP 2.6.i, the predecessor to PGP 2.6.3i.

Commercial Use

PGP 2.6.3i may be freely used for non-commercial purposes only. If you want to use PGP for commercial purposes, you need to buy a separate license for the IDEA algorithm used in PGP. IDEA licenses can be purchased from Ascom Systec AG in Switzerland. The fee is charged on a per-user basis as follows:
   1.. 10 users    120 SFr. per copy
  11.. 20 users     80 SFr. per copy 
  21..100 users     60 SFr. per copy
For more information, contact:

Ascom Systec AG
IDEA Licensing
CH-5506 Maegenwil

Phone : +41 62 889 59 54
Fax : +41 62 889 59 54
Email :

Comments and Bug Reports

PGP 2.6.3i was put together by Stale Schumacher <> with the help of many individuals around the world (see the file pgp263i.dif for a list of names). All questions regarding PGP 2.6.3i should be addressed to Please note that PRZ, MIT and the University of Oslo have nothing to do with this release. Comments, bug reports and suggestions for future releases are welcome.

I want to know more!

If you want to find out more about PGP and encryption in general, there are a number of resources available, both on paper and in electronic form. Here are a few, to get you started:





PGP 2.6.3i FAQ PGP FAQs from Where to Get the Latest PGP Program FAQ


alt.anonymous discussion of anonymity and anon remailers alt.anonymous.messages for anonymous encrypted message transfer alt.privacy.clipper Clipper, Capstone, Skipjack, Key Escrow general security discussions index to discussion of PGP discussion of RIPEM key distribution via Usenet alt.society.civil-liberty general civil liberties, including privacy comp.compression discussion of compression algorithms news reports from EFF discussion of EFF related issues comp.patents discussion of S/W patents, including RSA comp.risks some mention of crypto and wiretapping comp.society.privacy general privacy issues announcements of security holes software patents, copyrights, computer laws sci.crypt methods of data encryption/decryption sci.math general math discussion talk.politics.crypto general talk on crypto politics


The Official PGP User's Guide
by Philip R. Zimmermann
MIT Press 1995
ISBN 0-262-74017-6
216 pp. $14.95

PGP: Pretty Good Privacy
by Simson Garfinkel
O'Reilly & Associates 1994
ISBN 1-56592-098-8
430 pp. $24.95

Protect Your Privacy: The PGP User's Guide
by William Stallings
Prentice Hall PTR 1995
ISBN 0-13-185596-4
302 pp. $19.95

Applied Cryptography: Protocols, Algorithms, and Source Code in C
2nd Edition
by Bruce Schneier
John Wiley & Sons 1996
ISBN 0-471-11709-9

E-Mail Security with PGP and PEM: How to Keep Your Electronic Mail Private
by Bruce Schneier
John Wiley & Sons 1995
ISBN 0-471-05318-X

PGP main page
Meine Homepage
UNIX-AG Homepage