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PGP Frequently Asked Questions with Answers, Part 1/3

( Part1 - Part2 - Part3 )
[ Usenet FAQs | Web FAQs | Documents | RFC Index | Schools ]
Archive-name: pgp-faq/part1
Posting-Frequency: monthly
Last-modified: 22 June 1995

See reader questions & answers on this topic! - Help others by sharing your knowledge
-----BEGIN PGP SIGNED MESSAGE-----

                     Frequently Asked Questions
                          alt.security.pgp
                            25 May 1995

========================================================================
                       IMPORTANT DISCLAIMER!

     The use of PGP raises  a number of political  and legal
     issues.  I AM NOT a lawyer and AM NOT qualified to give
     any legal opinions.  Nothing in this document should be
     interpreted  as legal advice.   If you  have any  legal
     questions concerning the use of PGP, you should consult
     an  attorney who  specializes in  patent and/or  export
     law.   In any case,  the law  will vary from country to
     country.
========================================================================

Introduction

This is the list of Frequently Asked Questions for the Pretty Good
Privacy (PGP) encryption program written by Phillip Zimmermann.  It
is one of two FAQ lists for the newsgroup alt.security.pgp.

The other FAQ list is the "Where to Get PGP" FAQ, which is written and
maintained by Michael Paul Johnson <mpj@netcom.com>.  It covers many
topics this one does not; in particular, it contains more complete
information on sites that distribute PGP and the legal and technical
questions surrounding its distribution.  You may get a current copy
from:

  ftp://ftp.csn.net/mpj/getpgp.asc

This FAQ is slanted towards the DOS or Unix users of PGP and many of
the examples given may only apply to them.  For other systems, I would
like to direct your attention to the following documents:

  MAC: "Here's How to MacPGP!" by Xenon <an48138@anon.penet.fi>
  Archimedes PGP comes with its own PGPhints file.
  Send e-mail to pgpinfo@mantis.co.uk for a list of PGP tips.

It should be noted that most of the questions and answers concerning
PGP apply equally well to the ViaCrypt(tm) version.

Material for this FAQ has come from many different sources.  It would
be difficult to name each of the contributors individually, but I
would like to thank them as a group for their assistance.

A current copy of this FAQ can be retrieved from my WWW home page:

  http://www.prairienet.org/~jalicqui/pgpfaq.txt

or via FTP:

  ftp://ftp.prairienet.org/pub/providers/pgp/

The ? indicates the file format: clearsigned text (txt), gzipped
version of clearsigned text (txt.gz), PGP-signed-and-compressed binary
(pgp), or ASCII armored PGP-signed-and-compressed file (asc).

The PGP FAQ is also posted to news.answers and alt.answers, and can be
found in any of the standard FAQ repositories in the three-part form
it is posted in.

Permission is granted to copy, archive, or otherwise make this FAQ
available in any way you please, with only the following restriction:
that in every place where this FAQ may be accessed, it must also be
reasonably easy for a user to access a copy of the FAQ with its PGP
signature(s) from me intact.  This ensures that uncorrupted copies of
the FAQ get propagated where those who care can check them, and also
preserves attributions, etc.  If you HTMLize this document, you can
tag the two links mentioned above if you want to avoid storing
multiple copies of the FAQ.

Future plans for the FAQ:

 - Mac section!
 - hypertexting it and making it available in various forms (LaTeX,
   HTML, texinfo, or some such)

Any corrections or suggestions should be sent to me.

Jeff Licquia
jalicqui@prairienet.org

========================================================================

Table of Contents

  1.  Introductory Questions
  1.1.  What is PGP?
  1.2.  Why should I encrypt my mail?  I'm not doing anything illegal!
  1.3.  What are public keys and private keys?
  1.4.  How much does PGP cost?
  1.5.  Is encryption legal?
  1.6.  Is PGP legal?
  1.7.  What's the current version of PGP?
  1.8.  Is there an archive site for alt.security.pgp?
  1.9.  Is there a commercial version of PGP available?
  1.10. Is PGP available as a programming library, so I can write
        programs that use it?
  1.11. What platforms has PGP been ported to?
  1.12. Where can I obtain PGP?
  1.13. I want to find out more!

  2.  Very Common Questions and Problems
  2.1.  Why can't a person using version 2.2 read my version 2.3 message?
  2.2.  Why can't a person using version 2.3 read my version 2.6 message?
  2.3.  Why does PGP complain about checking signatures every so often?
  2.4.  Why does it take so long to encrypt/decrypt messages?
  2.5.  How do I create a secondary key file?
  2.6.  How does PGP handle multiple addresses?
  2.7.  Where can I obtain scripts to integrate pgp with my email or news
        reading system?
  2.8.  How can I decrypt messages I've encrypted to others?
  2.9.  Why can't I generate a key with PGP for Unix?
  2.10. When I clearsign a document in PGP, it adds a "dash-space" to
        several of my lines.  What gives?

  3.  Security Questions
  3.1.  How secure is PGP?
  3.2.  Can't you break PGP by trying all of the possible keys?
  3.3.  How secure is the conventional cryptography (-c) option?
  3.4.  Can the NSA crack RSA?
  3.5.  Has RSA ever been cracked publicly?  What is RSA-129?
  3.6.  How secure is the "for your eyes only" option (-m)?
  3.7.  What if I forget my pass phrase?
  3.8.  Why do you use the term "pass phrase" instead of "password"?
  3.9.  What is the best way to crack PGP?
  3.10. If my secret key ring is stolen, can my messages be read?
  3.11. How do I choose a pass phrase?
  3.12. How do I remember my pass phrase?
  3.13. How do I verify that my copy of PGP has not been tampered with?
  3.14. I can't verify the signature on my new copy of MIT PGP with my
        old PGP 2.3a!
  3.15. How do I know that there is no trap door in the program?
  3.16. I heard that the NSA put a back door in MIT PGP, and that they
        only allowed it to be legal with the back door.
  3.17. Can I put PGP on a multi-user system like a network or a mainframe?
  3.18. Can I use PGP under a "swapping" operating system like Windows
        or OS/2?
  3.19. Why not use RSA alone rather than a hybrid mix of IDEA, MD5, & RSA?
  3.20. Aren't all of these security procedures a little paranoid?
  3.21. Can I be forced to reveal my pass phrase in any legal proceedings?

  4.  Keys
  4.1.  Which key size should I use?
  4.2.  Why does PGP take so long to add new keys to my key ring?
  4.3.  How can I extract multiple keys into a single armored file?
  4.4.  I tried encrypting the same message to the same address two different
        times and got completely different outputs. Why is this?
  4.5.  How do I specify which key to use when an individual has 2 or more
        public keys and the very same user ID on each, or when 2 different
        users have the same name?
  4.6.  What does the message "Unknown signator, can't be checked" mean?
  4.7.  How do I get PGP to display the trust parameters on a key?
  4.8.  How can I make my key available via finger?

  5.  Message Signatures
  5.1.  What is message signing?
  5.2.  How do I sign a message while still leaving it readable?
  5.3.  Can't you just forge a signature by copying the signature
        block to another message?
  5.4.  Are PGP signatures legally binding?

  6.  Key Signatures
  6.1.  What is key signing?
  6.2.  How do I sign a key?
  6.3.  Should I sign my own key?
  6.4.  Should I sign X's key?
  6.5.  How do I verify someone's identity?
  6.6.  How do I know someone hasn't sent me a bogus key to sign?
  6.7.  What's a key signing party?
  6.8.  How do I organize a key signing party?

  7.  Revoking a key
  7.1.  My secret key ring has been stolen or lost, what do I do?
  7.2.  I forgot my pass phrase. Can I create a key revocation certificate?

  8.  Public Key Servers
  8.1.  What are the Public Key Servers?
  8.2.  What public key servers are available?
  8.3.  What is the syntax of the key server commands?

  9.  Bugs

  10. Recommended Reading

  11. General Tips

  Appendix I    - PGP add-ons and Related Products
  Appendix II   - Glossary of Cryptographic Terms
  Appendix III  - Cypherpunks
  Appendix IV   - Testimony of Philip Zimmermann to Congress
  Appendix V    - Announcement of Philip Zimmermann Defense Fund
  Appendix VI   - A Statement from ViaCrypt Concerning ITAR

========

1.    Introductory Questions

========

1.1.  What is PGP?

PGP is a program that gives your electronic mail something that it
otherwise doesn't have: Privacy. It does this by encrypting your mail
so that nobody but the intended person can read it. When encrypted,
the message looks like a meaningless jumble of random characters. PGP
has proven itself quite capable of resisting even the most
sophisticated forms of analysis aimed at reading the encrypted text.

PGP can also be used to apply a digital signature to a message without
encrypting it.  This is normally used in public postings where you
don't want to hide what you are saying, but rather want to allow
others to confirm that the message actually came from you. Once a
digital signature is created, it is impossible for anyone to modify
either the message or the signature without the modification being
detected by PGP.

While PGP is easy to use, it does give you enough rope so that you can
hang yourself. You should become thoroughly familiar with the various
options in PGP before using it to send serious messages. For example,
giving the command "PGP -sat <filename>" will only sign a message, it
will not encrypt it. Even though the output looks like it is
encrypted, it really isn't. Anybody in the world would be able to
recover the original text.

========

1.2. Why should I encrypt my mail?  I'm not doing anything illegal!

You should encrypt your e-mail for the same reason that you don't
write all of your correspondence on the back of a post card. E-mail is
actually far less secure than the postal system. With the post office,
you at least put your letter inside an envelope to hide it from casual
snooping. Take a look at the header area of any e-mail message that
you receive and you will see that it has passed through a number of
nodes on its way to you. Every one of these nodes presents the
opportunity for snooping.  Encryption in no way should imply illegal
activity.  It is simply intended to keep personal thoughts personal.

Xenon <an48138@anon.penet.fi> puts it like this:

Crime? If you are not a politician, research scientist, investor, CEO,
lawyer, celebrity, libertarian in a repressive society, investor, or
person having too much fun, and you do not send e-mail about your
private sex life, financial/political/legal/scientific plans, or
gossip then maybe you don't need PGP, but at least realize that
privacy has nothing to do with crime and is in fact what keeps the
world from falling apart. Besides, PGP is FUN. You never had a secret
decoder ring? Boo!  -Xenon (Copyright 1993, Xenon)

========

1.3.  What are public keys and private keys?

With conventional encryption schemes, keys must be exchanged with
everyone you wish to talk to by some other secure method such as face
to face meetings, or via a trusted courier.  The problem is that you
need a secure channel before you can establish a secure channel!  With
conventional encryption, either the same key is used for both
encryption and decryption or it is easy to convert either key to the
other. With public key encryption, the encryption and decryption keys
are different and it is impossible for anyone to convert one to the
other. Therefore, the encryption key can be made public knowledge, and
posted in a database somewhere. Anyone wanting to send you a message
would obtain your encryption key from this database or some other
source and encrypt his message to you. This message can't be decrypted
with the encryption key. Therefore nobody other than the intended
receiver can decrypt the message. Even the person who encrypted it can
not reverse the process. When you receive a message, you use your
secret decryption key to decrypt the message. This secret key never
leaves your computer. In fact, your secret key is itself encrypted to
protect it from anyone snooping around your computer.

========

1.4.  How much does PGP cost?

Nothing! (Compare to ViaCrypt PGP at $98!)  

It should be noted, however, that in the United States, some freeware
versions of PGP *MAY* be a violation of a patent held by Public Key
Partners (PKP).  The MIT and ViaCrypt versions specifically are not in
violation; if you use anything else, it's your risk.  See below
(question 1.6) for more information on the patent situation.

Also, the free versions of PGP are free only for noncommercial use.
If you need to use PGP in a commercial setting (and you live in the
United States or Canada), you should buy a copy of ViaCrypt PGP.
ViaCrypt PGP has other advantages as well, most notably a limited
license to export it to foreign branch offices.  See below, under
question 1.10, for information on how to contact ViaCrypt.

If you need to use PGP for commercial use outside the United States or
Canada, you should contact Ascom Systec AG, the patent holders for IDEA.
They have sold individual licenses for using the IDEA encryption in
PGP.  Contact:

  Erhard Widmer
  Ascom Systec AG
  Dep't. CMVV
  Gewerbepark
  CH-5506 Maegenwil
  Switzerland
  IDEA@ascom.ch

  ++41 64 56 59 83 (Fax ++41 64 56 59 90)

========

1.5.  Is encryption legal?

In much of the civilized world, encryption is either legal, or at
least tolerated. However, there are a some countries where such
activities could put you in front of a firing squad! Check with the
laws in your own country before using PGP or any other encryption
product. A couple of the countries where encryption is illegal are
France, Iran, and Iraq.

*** NEWS FLASH ***

On April 3, 1995, Boris Yeltsin issued a decree formally banning
encryption with methods not approved by the state.  This would,
presumably, include PGP.  Thus, Russia must be added to the short list
above.

*** END NEWS FLASH ***

The legal status of encryption in many countries has been placed on
the World Wide Web.  You can access it from:

  http://web.cnam.fr/Network/Crypto/

========

1.6.  Is PGP legal?

In addition to the comments about encryption listed above, there are a
couple of additional issues of importance to those individuals
residing in the United States or Canada.  

First, there is a question as to whether or not PGP falls under ITAR
regulations which govern the exporting of cryptographic technology
from the United States and Canada. This despite the fact that
technical articles on the subject of public key encryption have been
available legally worldwide for a number of years.  Any competent
programmer would have been able to translate those articles into a
workable encryption program.  A lawsuit has recently been filed by the
EFF challenging the ITAR regulations; thus, they may be relaxed to
allow encryption technology to be exported.

Second, older versions of PGP (up to 2.3a) were thought to be
violating the patent on the RSA encryption algorithm held by Public
Key Partners (PKP), a patent that is only valid in the United States.
This was never tested in court, however, and recent versions of PGP
have been made with various agreements and licenses in force which
effectively settle the patent issue.  So-called "international"
versions and older versions (previous to ViaCrypt PGP 2.4), however,
are still considered in violation by PKP; if you're in the USA, use
them at your own risk!

========

1.7.  What's the current version of PGP?

You would think that's an easy question to answer!

At the moment, there are four different "current" versions of PGP.
All of these are derived, more or less, from a common source base: PGP
2.3a, the last "guerillaware" version of PGP.  Negotiations to make
PGP legal and "legitimate" have resulted in the differing versions
available; all of them, for the most part, are approximately
equivalent in functionality, and they can all work with each other in
most respects.

MIT PGP 2.6.2 is the current "official" freeware version.  It has been
developed both with Phil Zimmermann's approval and active involvement.
It contains several bug fixes and enhancements over 2.3a, and it
avoids the patent question surrounding other versions of PGP by using
the RSAREF library for some of its functions.  This library was
developed by RSA Data Security, Inc., and is (basically) free for
noncommercial use.  As part of MIT's agreement with RSADSI, all
versions of MIT PGP generate encrypted messages that cannot be
decrypted with PGP 2.3a or previous versions.

ViaCrypt PGP 2.7.1 is the current "official" commercial version.  It
is available from ViaCrypt, a company out of Arizona, and also has
Phil's approval and involvement.  See below for details on this
version.

PGP 2.6.2i ("international") is a version of PGP developed from the
source code of MIT PGP, which was exported illegally from the United
States at some point.  Basically, it is MIT PGP 2.6.2, but it uses the
old encryption routines from PGP 2.3a; these routines perform better
than RSAREF and in addition do not have the usage restrictions in the
RSAREF copyright license.  It also contains some fixes for bugs
discovered since the release of MIT PGP 2.6.2.

PGP 2.6ui ("unofficial international") is PGP 2.3a with minor
modifications made so it can decrypt files encrypted with MIT PGP.  It
does not contain any of the MIT fixes and improvements; it does,
however, have other improvements, most notably in the Macintosh
version.

========

1.8.  Is there an archive site for alt.security.pgp?

laszlo@instrlab.kth.se (Laszlo Baranyi) says:

"My memory says that ripem.msu.edu stores a backlog of both
alt.security.pgp, and sci.crypt. But that site is ONLY open for ftp
for those that are inside US."

========

1.9.  Is there a commercial version of PGP available?

Yes; by arrangement with the author of PGP, a company called ViaCrypt
is marketing a version of PGP that is almost identical to the freeware
version. Each can read or write messages which the other can
understand.

ViaCrypt reports:

- -----
If you are a commercial user of PGP in the USA or Canada, contact
Viacrypt in Phoenix, Arizona, USA.  The commercial version of PGP
is fully licensed to use the patented RSA and IDEA encryption
algorithms in commercial applications, and may be used in
corporate and government environments in the USA and Canada.  It
is fully compatible with, functionally the same as, and just as
strong as the freeware version of PGP. Due to limitations on
ViaCrypt's RSA distribution license, ViaCrypt only distributes
executable code and documentation for it, but they are working on
making PGP available for a variety of platforms.  Call or write
to them for the latest information.  The latest version number
for Viacrypt PGP is 2.7.  [Note: Since this statement was issued,
ViaCrypt has updated ViaCrypt PGP to 2.7.1.]

Here is a brief summary of Viacrypt's currently-available
products:

1. ViaCrypt PGP for Windows (3.1).   Prices start at $124.98

2. ViaCrypt PGP for Macintosh, 680x0 or PowerPC, System 6.04 or   
   later.    Prices start at $124.98

3. ViaCrypt PGP for MS-DOS.  Prices start at $99.98

4. ViaCrypt PGP for UNIX.  Includes executables for the following
   platforms:

     SunOS 4.1.x (SPARC)
     Solaris 2.3
     IBM RS/6000 AIX
     HP 9000 Series 700/800 UX
     SCO 386/486 UNIX
     SGI IRIX
     AViiON DG-UX(88/OPEN)

   Prices start at $149.98

     Executables for the following additional platforms are
     available upon request for an additional $30.00 charge.

     BSD 386
     Ultrix MIPS DECstation 4.x
     DEC Alpha OSF/1
     NeXTSTEP

5. ViaCrypt PGP for WinCIM/CSNav.  A special package for users of 
   CompuServe.  Prices start at $119.98

If you wish to place an order please call 800-536-2664 during the
hours of 8:30am to 5:00pm MST, Monday - Friday.  We accept VISA,
MasterCard, AMEX and Discover credit cards.

If you have further questions, please feel free to contact me.

Best Regards,
Paul E. Uhlhorn
Director of Marketing, ViaCrypt Products
Mail:       9033 N. 24th Avenue
            Suite 7
            Phoenix, AZ  85021-2847
Phone:      (602) 944-0773
Fax:        (602) 943-2601
Internet:   viacrypt@acm.org
Compuserve: 70304,41
- -----

They have also reported recently that they have gained a general
export license for exporting ViaCrypt PGP to foreign subsidiaries of
USA-based companies.  Contact ViaCrypt for details.

========

1.10. Is PGP available as a programming library, so I can write
      programs that use it?

Not yet.  PGP 3.0, when it is released, is supposed to have support
for doing this.  The PGP development team has even released a
preliminary API for the library; you can get it from:

  ftp://ftp.netcom.com/pub/dd/ddt/crypto/crypto_info/

The development team has expressed that this is not a definitive spec;
some of it is already out of date.  It's good for getting the general
idea, though.  Send comments concerning the spec to pgp@lsd.com.

In the meantime, you can write your programs to call the PGP program
when necessary.  In C, for example, you would likely use the system()
or spawn...() functions to do this.

========

1.11. What platforms has PGP been ported to?

PGP has been ported successfully to many different platforms,
including DOS, the Macintosh, OS/2, Unix (just about all flavors),
VMS, the Atari ST, Archimedes, and the Commodore Amiga.  A Windows NT
port is reportably in the works as well.

If you don't see your favorite platform above, don't despair!  It's
likely that porting PGP to your platform won't be too terribly
difficult, considering all the platforms it has been ported to.  Just
ask around to see if there might in fact be a port to your system, and
if not, try it!

PGP's VMS port, by the way, has its own Web page:

  http://www.tditx.com/~d_north/pgp.html

========

1.12. Where can I obtain PGP?

PGP is very widely available, so much so that a separate FAQ has been
written for answering this question.  It is called, "WHERE TO GET THE
PRETTY GOOD PRIVACY PROGRAM (PGP)"; it is posted in alt.security.pgp
regularly, is in the various FAQ archive sites, and is also available
from:

  ftp://ftp.csn.net/mpj/getpgp.asc

However, I will describe below the ways to get the differing versions
of PGP from their source sites.  Please refer to the above document
for more information.

MIT PGP 2.6.2:

Due to the ITAR regulations (described above), MIT has found it
necessary to place PGP in an export-controlled directory to prevent
people outside the United States from downloading it.  If you are in
the USA, you may follow these directions:

Telnet to net-dist.mit.edu and log in as "getpgp".  You will then be
given a short statement about the regulations concerning the export of
cryptographic software, and be given a series of yes/no questions to
answer.  If you answer correctly to the questions (they consist mostly
of agreements to the RSADSI and MIT licenses and questions about
whether you intend to export PGP), you will be given a special
directory name in which to find the PGP code.  At that point, you can
FTP to net-dist.mit.edu, change to that directory, and access the
software.  You may be denied access to the directories even if you
answer the questions correctly if the MIT site cannot verify that your
site does in fact reside in the USA.

Further directions, copies of the MIT and RSAREF licenses, notes, and
the full documentation are freely available from:

  ftp://net-dist.mit.edu/pub/PGP/

An easier method of getting to the PGP software is now available on
the World Wide Web at the following location:

  http://bs.mit.edu:8001/pgp-form.html

ViaCrypt PGP 2.7.1:

ViaCrypt PGP is not generally available for FTP; it is commercial
software.  It is, furthermore, not available outside the United States
or Canada except under special circumstances.  See above (question
1.9) for contact information.

PGP 2.6.2i:

As Norway is not limited by ITAR, no hoops are needed to get this
version:

  http://www.ifi.uio.no/~staalesc/PGP/home.html
  ftp://ftp.ox.ac.uk/pub/crypto/pgp/

You may also get it via mail by sending a message to
hypnotech-request@ifi.uio.no with your request in the subject:

  GET pgp262i[s].[zip | tar.gz]

Specify the "s" if you want the source code.  Putting ".zip" at the
end gets you the files in the PKZIP/Info-ZIP archive format, while
putting "tar.gz" at the end gets the files in a gzipped tar file.

PGP 2.6ui:

  ftp://ftp.mantis.co.uk/pub/cryptography/
  http://www.mantis.co.uk/pgp/pgp.html

This link is also an excellent resource for other information about PGP.

A note on ftpmail:

    For those individuals who do not have access to FTP, but do have access
    to e-mail, you can get FTP files mailed to you.  For information on
    this service, send a message saying "Help" to ftpmail@decwrl.dec.com.
    You will be sent an instruction sheet on how to use the ftpmail
    service.

========

1.13.  I want to find out more!

If this FAQ doesn't answer your question, there are several places for
finding out information about PGP.

Web/Mosaic/Lynx:

    Fran Litterio's Crypto Page (from the Virtual Library)
      http://draco.centerline.com:8080/~franl/crypto.html
    Using Microsoft Windows with PGP
      http://www.lcs.com/winpgp.html
    Derek Atkins' Official Bug List for MIT PGP
      http://www.mit.edu:8001/people/warlord/pgp-faq.html
    The Phil Zimmermann Legal Defense Fund Page
      http://www.netresponse.com/zldf
    The MCIP/Macintosh Cryptography Page
      http://uts.cc.utexas.edu/~grgcombs/htmls/crypto.html
    Jeff Licquia's Home Page
      http://www.prairienet.org/~jalicqui

FTP Sites:

    ftp://ripem.msu.edu/pub/crypt/
    ftp://ftp.dsi.unimi.it/pub/security/crypt/
    ftp://ftp.csua.berkeley.edu/pub/cypherpunks/

News Groups:

    alt.anonymous               Discussion of anonymity and anon remailers
    alt.anonymous.messages      For anonymous encrypted message transfer
    alt.privacy.clipper         Clipper, Capstone, Skipjack, Key Escrow
    alt.security                general security discussions
    alt.security.index          index to alt.security
    alt.security.pgp            discussion of PGP
    alt.security.ripem          discussion of RIPEM
    alt.security.keydist        key distribution via Usenet
    alt.society.civil-liberty   general civil liberties, including privacy
    comp.compression            discussion of compression algorithms
    comp.org.eff.news           News reports from EFF
    comp.org.eff.talk           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
    comp.security.announce      announcements of security holes
    misc.legal.computing        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

========

2.   Very Common Questions and Problems

========

2.1. Why can't a person using version 2.2 read my version 2.3 message?

You might try adding "+pkcs_compat=0" to your command line as follows:
"pgp -seat +pkcs_compat=0 <filename>" By default, versions 2.3 and
later of PGP uses a different header format that is not compatible
with earlier versions of PGP. Inserting this option into the command
will force PGP to use the older header format. You can also set this
option in your config.txt file, but this is not recommended, as the
newer versions of PGP cannot understand the old signature format.

========

2.2. Why can't a person using version 2.x read my version 2.6 message?

You are probably using MIT PGP, or possibly some other version of PGP
with the "legal_kludge" option turned off.

As part of the agreement made to settle PGP's patent problems, MIT PGP
changed its format slightly to prevent PGP 2.4 and older versions
from decrypting its messages.  This format change was written into MIT
PGP to happen on September 1, 1994.  Thus, all messages encrypted with
MIT PGP after that date are unreadable by 2.4 (and earlier).

The best route here is for your friend to upgrade to a newer version
of PGP.  Alternatively, if you are using a non-MIT version, look up
the "legal_kludge" option in your documentation; you should be able to
configure your copy of PGP to generate old-style messages.

========

2.3. Why does PGP complain about checking signatures every so often?

Version 2.3a introduced the "pkcs_compat" option, allowing the format
of signatures to change slightly to make them more compatible with
industry standards.  (See question 2.1.)  MIT PGP, because it uses the
RSAREF library, is unable to understand the old signature format, so
it therefore ignores the signature and warns you that it is doing so.

This problem comes up mostly with old key signatures.  If your key
contains such old signatures, try to get those people who signed your
key to resign it.

If an old signature is still vitally important to check, get a non-MIT
version of PGP to check it with, such as ViaCrypt's.

========

2.4. Why does it take so long to encrypt/decrypt messages?

This problem can arise when you have placed the entire public key ring
from one of the servers into the pubring.pgp file. PGP may have to
search through several thousand keys to find the one that it is after.
The solution to this dilemma is to maintain 2 public key rings. The
first ring, the normal pubring.pgp file, should contain only those
individuals that you send messages to quite often. The second key ring
can contain ALL of the keys for those occasions when the key you need
isn't in your short ring. You will, of course, need to specify the key
file name whenever encrypting messages using keys in your secondary
key ring. Now, when encrypting or decrypting messages to individuals
in your short key ring, the process will be a LOT faster.

========

2.5. How do I create a secondary key file?

First, let's assume that you have all of the mammoth public key ring
in your default pubring.pgp file. First, you will need to extract all
of your commonly used keys into separate key files using the -kx
option. Next, rename pubring.pgp to some other name. For this example,
I will use the name "pubring.big". Next, add each of the individual
key files that you previously created to a new pubring.pgp using the
- -ka option. To encrypt a message to someone in the short default file,
use the command "pgp -e <file> <userid>". To encrypt a message to
someone in the long ring, use the command "pgp -e
+pubring=c:\pgp\pubring.big <file> <userid>". Note that you need to
specify the complete path and file name for the secondary key ring. It
will not be found if you only specify the file name.

========

2.6. How does PGP handle multiple addreses?

When encrypting a message to multiple addresses, you will notice that
the length of the encrypted file only increases by a small amount for
each additional address.  The reason that the message only grows by a
small amount for each additional key is that the body of the message
is only encrypted once using a random session key and IDEA. It is only
necessary then to encrypt this session key once for each address and
place it in the header of the message. Therefore, the total length of
a message only increases by the size of a header segment for each
additional address. (To avoid a known weakness in RSA when encrypting
the same message to multiple recipients, the IDEA session key is
padded with different random data each time it is RSA- encrypted.)

========

2.7. Where can I obtain scripts to integrate pgp with my email or news
reading system?

There are many scripts and programs available for making PGP easier to
use.  See below, in Appendix I, for a list of such programs.

A set of scripts was distributed with PGP for doing this.  Since these
scripts were considered out of date, they have been removed from the
MIT distribution.

========

2.8. How can I decrypt messages I've encrypted to others?

With conventional encryption, you can read the message by running PGP
on the encrypted file and giving the pass phrase you used to encrypt.

With regular encryption, it's impossible unless you encrypted to
yourself as well.  Sorry!

There is an undocumented setting, EncryptToSelf, which you can set in
your CONFIG.TXT or on the command line to "on" if you want PGP to
always encrypt your messages to yourself.  Be warned, though; if your
key is compromised, this means that the "cracker" will be able to read
all the message you sent as well as the ones you've received.

========

2.9. Why can't I generate a key with PGP for Unix?

Most likely this is caused because PGP can't create the public and
private key ring files.  If PGPPATH isn't defined, PGP will try to put
those files in the subdirectory ".pgp" off your home directory.  It
will not create the directory if needed, so if the directory's not
there already, PGP will crash after generating the key.

There are two solutions: set the PGPPASS environment variable to point
to the location of your key rings, or run a "mkdir $HOME/.pgp" before
generating your key.

========

2.10. When I clearsign a document in PGP, it adds a "dash-space" to
several of my lines.  What gives?

PGP does this because of the "-----BEGIN PGP MESSAGE-----" (and
related) headers it uses to mark the beginning of PGP messages.  To
keep it from getting confused, it tacks a "- " to the beginning of
every line in the regular text which has a dash at the start.  It
strips the extra dash and space when you check the message's
signature, and writes the original text to the output.


-----BEGIN PGP SIGNATURE-----
Version: 2.6.2

iQCVAwUBL+kAVLnwkw8DU+OFAQGTaQP/am6VQIXoSRvYsxw9ncyPmZDN+t/0r1+0
osArYuWC167qo+hIBUcEwabRiLt2TvbTG91qjqTOUwkU+qB/eAj96ozHlN22AmmR
7ufvJAR4HjJFB+QBv5aFVB3/FTPoupDCnA6L79O4xXFHoBhxukYSJ5zswAZdVSbZ
bY8ALveqhpY=
=9GgA
-----END PGP SIGNATURE-----

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