Archive-name: ripem/faq
Last-update: 31 Mar 93 22:00:00 -0500

ABOUT THIS POSTING
------------------
This is a listing of likely questions and information about RIPEM, a
program for public key mail encryption.  It (this FAQ, not RIPEM) was
written and will be maintained by Marc VanHeyningen
<mvanheyn@cs.indiana.edu>.  It will be posted to a variety of
newsgroups on a monthly basis; follow-up discussion specific to RIPEM
is redirected to the group alt.security.ripem.

WHAT'S NEW
----------
I am now running a World Wide Web archive of RIPEM information.  It
does not contain much of anything that isn't available elsewhere, but
it has convenient pointers to the most current version of this FAQ and
some other stuff.  The URL is "http://cs.indiana.edu/ripem/dir.html".

This month's version has a fair amount of new pointers to information
on patents and stuff like that.  I've also reordered a few things to
have a more sensible ordering.  I hope I don't have to edit this again
soon. :-)

DISCLAIMER
----------
Nothing in this FAQ should be considered legal advice, or anything
other than one layperson's opinion.  If you want real legal advice,
talk to a real lawyer, preferably one with experience in patent law,
export regulations, or whatever area of law is in question.

LIST OF QUESTIONS
-----------------
1)  What is RIPEM?
2)  How can I get RIPEM?
3)  Will RIPEM run on my machine?
4)  Will RIPEM work with my mailer?
5)  What is RSA?
6)  What is DES?
7)  What is a fingerprint, like MD5?
8)  What is PEM?
9)  What's this about distributing and authenticating keys?
10)  Isn't it a bad idea to use patented algorithms in standards like PEM?
11)  What about RSADSI/PKP?
12)  Why do all RIPEM public keys look very similar?
13)  What is PGP?
14)  What about RPEM?
15)  What is MIME?
16)  What is TIS/PEM?
17)  I have this simple way to defeat the security of RIPEM...

QUESTIONS AND ANSWERS
---------------------

1)  What is RIPEM?

 RIPEM is a (not yet complete, but useful) implementation of Privacy
 Enhanced Mail (PEM).  RIPEM allows your electronic mail to have the
 four security facilities provided by PEM: disclosure protection
 (optional), originator authenticity, message integrity measures, and
 non-repudiation of origin (always).  (See: "What is PEM?")

 RIPEM was written primarily by Mark Riordan <mrr@scss3.cl.msu.edu>.
 Most of the code is in the public domain, except for the RSA routines,
 which are a library called RSAREF licensed from RSA Data Security Inc.

 The current version of RIPEM is 1.0.5; the current version of the
 Macintosh port of RIPEM is 0.7.

2)  How can I get RIPEM?

 RIPEM uses the library of cryptographic routines RSAREF, which is
 considered munitions and thus is export-restricted from distribution
 to persons who are not citizens or permanent residents in the U.S or
 Canada without an export license.  No such license has been obtained
 (nor would one likely be granted unless the RSA key exchange were
 shortened to 512 bits and the symmetric cipher changed to something
 weaker than DES.  There are some suggestions that this situation may
 change now that Clinton is in office.)  The author requests in the
 README file that this law not be violated:

 #Please do not export the cryptographic code in this distribution
 #outside of the USA or Canada.  This is a personal request from me,
 #the author of RIPEM, and a condition of your use of RIPEM.

 Note that RSAREF is not in the public domain, and a license for it is
 included with the distribution.  You should read it before using
 RIPEM.

 RIPEM is available via anonymous FTP to citizens and permanent
 residents in the U.S. from rsa.com; cd to rsaref/ and read the README
 file for info.  Note that the non-RSAREF portion of RIPEM is not a
 product of RSA Data Security, Incorporated; they merely are helping
 distribute it.

 RIPEM, as well as some other crypt stuff, has its "home site" on
 ripem.msu.edu, which is open to non-anonymous FTP for users in the
 U.S. and Canada who are citizens or permanent residents.  To find out
 how to obtain access, FTP there, cd to pub/crypt/, and read the file
 GETTING_ACCESS.  For convenience, binaries for many architectures are
 available here in addition to the full source tree.

3)  Will RIPEM run on my machine?

 Probably.  It has already been ported to MS-DOS and most flavors of
 Unix (SunOS, NeXT, Linux, AIX, ULTRIX, Solaris, etc.)  Ports to
 Macintosh include a standard UNIX-style port and a rather nice
 Mac-like port written by Raymond Lau, author of StuffIt.  More ports
 are expected, and help of users is invited.

4)  Will RIPEM work with my mailer?

 Probably.  How easy and clean the effective interface is will depend
 on the sophistication and modularity of the mailer, though.  The users
 guide, included with the distribution, discusses ways to use RIPEM
 with many popular mailers, including Berkeley, mush, Elm, and MH.
 Code is also included in elisp to allow easy use of RIPEM inside GNU
 Emacs.

 If you make a new interface for RIPEM or create an improvement on one
 in the distribution which you believe is convenient to use, secure,
 and may be useful to others, feel free to post it to alt.security.ripem.

5)  What is RSA?

 RSA is a crypto system which is asymmetric, or public-key.  This means
 that there are two different, related keys: one to encrypt and one to
 decrypt.  Because one cannot (reasonably) be derived from the other,
 you may publish your encryption, or public, key widely and keep your
 decryption, or private, key to yourself.  Anyone can use your public
 key to encrypt a message, but only you hold the private key needed to
 decrypt it.  Note that the "message" sent with RSA is normally just
 the DES key to the real plaintext. (See "What is DES?")

 Note that the above only provides for disclosure protection.  For
 originator authenticity, message integrity, and non-repudiation of
 origin services to be implemented, the fingerprint of the message
 (See "What is a fingerprint, like MD5?") is encrypted with the
 sender's private key.  The recipient, or a dispute-resolving
 authority, can use the sender's public key to decrypt it and confirm
 that the message must have come from the sender and was not altered.

 RSA was named for the three men (Rivest, Shamir and Adleman) who
 invented it.  To find out lots more about RSA and modern cryptography
 in general, ftp to rsa.com and look in pub/faq/.  Some information
 also may be in sci.crypt.

6)  What is DES?

 DES is the Data Encryption Standard, a widely used symmetric, or
 secret-key, crypto system.  Unlike RSA, DES uses the same key to
 encrypt and decrypt messages.  However, DES is much faster than RSA.

 RIPEM uses both DES and RSA; it generates a random key and encrypts
 your mail with DES using that key.  It then encrypts that key with the
 recipient's public RSA key and includes the result in the letter,
 allowing the recipient to recover the DES key.

 DES is sometimes considered weak because it is somewhat old and uses a
 key length considered too short by modern standards.  However, it
 should be reasonably safe against an opponent smaller than a large
 corporation or government agency.  It is not likely that the PEM
 standard will incorporate support for other symmetric ciphers in the
 near future, because there is a strong feeling that PEM should be
 stable so it can become utilized widely without early problems with
 interoperability.

7)  What is a fingerprint, like MD5?

 MD5 is a message digest algorithm produced by RSA Data Security Inc.
 It provides a 128-bit fingerprint, or cryptographically secure hash,
 of the plaintext.  It is cryptographically secure because it is not
 possible (in a reasonable amount of computation) to produce a
 different plaintext which produces the same fingerprint.  Thus,
 instead of signing the entire message with the sender's private key,
 only the MD5 of the message needs to be signed for authentication.

 MD5s can also be exchanged directly for authentication; for example,
 RIPEM public keys include an MD5 of the public key in the file, so
 parties wishing to confirm their keys are authentic via a separate
 channel merely need exchange MD5s of keys and verify their accuracy.

 MD5 is sometimes used for other purposes; for example, it is often
 used to map an input of arbitrary length to 128 bits of data, as a
 passphrase interpreter or cookie generator.

 MD5 is described in its entirety (including an implementation in C) in
 RFC 1321.

 There have been some recent suggestions that MD5 may not be as strong
 a hash as was originally believed; presumably some other hash
 function will be used if this is accepted as true.

8)  What is PEM?

 PEM is Privacy Enhanced Mail, a standard for allowing transfer of
 encrypted electronic mail generated over a long period of time by a
 working group of experts.  It is described in RFCs 1421-1424; these
 documents have been approved and obsolete the old RFCs 1113-1115.

 RIPEM is not really a complete implementation of PEM, because PEM
 specifies certificates for authenticating keys, which RIPEM does not
 handle at this time.  Their addition is planned.

9)  What's this about distributing and authenticating keys?

 For a remote user to be able to send secure mail to you, she must know
 your public key.  For you to be able to confirm that the message
 received came from her, you must know her public key.  It is important
 that this information be accurate; if a "bad guy" convinces her that
 his key is in fact yours, she will send messages which he can read.

 RIPEM allows for three methods of key management: a central server,
 the distributed finger servers, and a flat file.  All three are
 described in the RIPEM users guide which is part of the distribution.
 None of them provide perfect security.  The PEM standard calls for
 key management by certificates; the addition of this feature to RIPEM
 is planned, but chicken-egg issues still exist.

10)  Isn't it a bad idea to use patented algorithms in standards like PEM?

 This issue has been considered in the standards process.  RFC 1310,
 the specification for Internet standards, has a discussion (section
 6) on what specifications for nondiscriminatory availability must be
 met for a patented method to be included in a standard.  RFC 1421
 addresses this issue with regard to the patents covering public-key
 cryptography.

 This does not, of course, mean that all questions are settled or that
 everyone is in agreement.  An interesting exchange on the use of
 patented algorithms in standards with regard to public-key
 cryptography is in the League for Programming Freedom archive
 (available via FTP: ftp.uu.net:/doc/lpf) in the files bidzos.letter
 and bidzos.response.  (Amusingly, the LPF files on ftp.uu.net are
 compressed with a patented algorithm.)

11)  What about RSADSI/PKP?

 RSA Data Security, Inc. (RSADSI) is a California-based company
 specializing in cryptographic technologies.  Public Key Partners is a
 firm which holds exclusive sub-licensing rights of the following U.S.
 patents and all of their corresponding foreign patents:

      Cryptographic Apparatus and Method
      ("Diffie-Hellman")............................... No. 4,200,770

      Public Key Cryptographic Apparatus
      and Method ("Hellman-Merkle").................... No. 4,218,582

      Cryptographic Communications System and
      Method ("RSA")................................... No. 4,405,829

      Exponential Cryptographic Apparatus
      and Method ("Hellman-Pohlig").................... No. 4,424,414

 PKP claims these four patents cover all known methods of public key
 cryptography.  The two businesses are rather closely related (for
 example, the same person, Jim Bidzos, is president of both of them.)
 PKP has licensed this technology to a considerable number of
 companies (IBM, DEC, Motorola, AT&T, Lotus...) for use in their
 products.  PKP has also threatened and filed lawsuits defending their
 patents.

 RIPEM was originally created with no connection to RSADSI other than
 its use of the RSAREF library, and for no reason other than its
 author's desire to see widespread use of public-key cryptography.
 However, after the ball started rolling, people at RSADSI got
 interested.  RSADSI decided to carry RIPEM on its FTP site, and some
 people there started making their own RIPEM keys and contributing
 code.  RIPEM even won the "Best Application Built on RSAREF in 1992"
 award.

12)  Why do all RIPEM public keys look very similar?

 RIPEM public keys begin with a PKCS (Public-Key Cryptography
 Standards) identifier describing various characteristics about the
 key, so the first bunch of characters in your key may be the same as
 those of lots of other people's keys.  This does not mean your keys
 are similar, but only that they are the same class of key, were
 generated with the same program, are of the same length, etc.

13)  What is PGP?

 PGP is another cryptographic mail program called Pretty Good Privacy.
 PGP has been around longer than RIPEM, and works somewhat differently.
 PGP is not compatible with RIPEM in any way, though PGP does also use RSA.

 A few major differences between PGP and RIPEM:

 - PGP has more key management features, particularly for users without
   a direct network connection.

 - RIPEM conforms to the PEM RFCs and thus has a greater probability
   of working with other PEM software.  PGP makes no attempt to be
   compatible with anything other than itself.

 - RIPEM uses RSAREF, a library of RSA routines from RSADSI which
   comes with a license allowing noncommercial use.  PGP uses its own
   implementation of RSA.  PKP claims that it is a violation of its
   patents to "make, use or sell" PGP in the U.S. or Canada without
   either a license or written permission.  (See: "DISCLAIMER")
   (See: "What about RSADSI/PKP?")  Phil Zimmermann, the author of
   PGP, stopped distributing it after being threatened with legal
   action; he believed that a licensing scheme could be arranged, but
   it hasn't happened and there seems little prospect of it happening
   in the future.  He acknowledges in the PGP User's Guide:

   #In fact, if you live in the USA, and you are not a Federal agency, 
   #you shouldn't actually run PGP on your computer, because Public
   #Key Partners wants to forbid you from running my software.  PGP is
   #contraband.

 - Both PGP and RIPEM are export-restricted, and cannot be sent outside
   the U.S. and Canada without an export license.  However, PGP
   already exists on many ftp sites in Europe and other places.

 Whether you use PGP or RIPEM or whatever, the documentation to PGP is
 recommended reading to anyone interested in such issues.
 Unfortunately, it's not distributed separately from the program,
 which can be difficult to find in the U.S. on FTP sites due to
 liability concerns.

14)  What about RPEM?

 RPEM stands for Rabin Privacy Enhanced Mail.  It was similar to RIPEM,
 but used a public-key cipher invented by Rabin (which is not RSA) in
 an attempt to avoid the patents on public-key systems.  It was
 written by Mark Riordan, who later wrote RIPEM.

 Its distribution was halted when, contrary to the beliefs of many
 (including Rabin), PKP claimed that their patents were broad enough
 to cover the cipher employed.  This claim is not universally
 accepted, but was not challenged for pragmatic reasons.

 RPEM is not really used anymore.  It is not compatible with RIPEM or PGP.

15)  What is MIME?

 MIME stands for Multipurpose Internet Mail Extensions, and is
 described in RFC 1341.  You can find out about it in the newsgroup
 comp.mail.mime; a FAQ exists on it.  How PEM should interact with
 MIME is not yet entirely clear; some people use the stopgap solution
 of having a MIME type application/x-ripem in order to send RIPEM
 messages as MIME ones.  I hope some standards will emerge.  Draft
 Internet documents exist on the matter.

16)  What is TIS/PEM?

 Trusted Information Systems is working on a version of Privacy
 Enhanced Mail for general availability.  Last I heard, it was
 rumored to be integrated into an existing mail user agent (MH)
 rather than a stand-alone system, and in beta test.  I don't know
 much more than that.

17)  I have this simple way to defeat the security of RIPEM...