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From: Marc VanHeyningen <mvanheyn@cs.indiana.edu> Subject: RIPEM Frequently Asked Questions Message-ID: <C7vnF5.24u@usenet.ucs.indiana.edu> Organization: Computer Science, Indiana University Date: Mon, 31 May 1993 06:01:53 GMT Lines: 406

Archive-name: ripem/faq Last-update: 30 May 1993 00:00:00 GMT

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".

The PGP section is now new and improved, with more quotations!

I'm now going to post the companion "RIPEM vulnerabilities" article less often, probably every 3 months.

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. Nothing that I say should be considered the opinions of Indiana University or the Computer Science Department; likewise, opinions of other persons quoted in this document should be considered their own, which may or may not represent the opinions of their affiliated institutions.

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?

Riordan's Internet Privacy Enhanced Mail (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 1.0.7 (1.1 RSN); the current version of the Macintosh port of RIPEM is 0.8b1.

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 were some suggestions that this situation may change now that Clinton is in office, but that is looking less and less likely.) 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 welcomed.

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. RIPEM will soon include a stronger system using multiple encryptions with DES.

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; however, thus far it is still regarded as secure.

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. They have already been added to the Macintosh version.

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 the hierarchy of certifying authorities is still developing and thus few people have certificates yet.

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.

11) What about RSADSI/PKP?

RSA Data Security, Inc. (RSADSI) is a California-based company specializing in cryptographic technologies. Public Key Partners (PKP) 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. PKP and RSADSI 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 for users without a direct network connection. Its key verification mechanism is non-hierarchical, which means it's more available today, while probably the best key distribution with RIPEM is to automatically finger the recipient for a public key.

* 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; i.e. it's not a "standard."

* 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 which is not licensed. (See: "DISCLAIMER") (See: "What about RSADSI/PKP?") There are rumors that a PGP-compatible product implemented with RSAREF is in the works.

Some various legal perspectives on using PGP in the U.S.:

``an illegal activity that violates patent and export law.'' - Jim Bidzos <jim@rsa.com>, President of PKP and RSADSI, _Wired_ (the magazine), May/June 1993

``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.''

- Phil Zimmermann <prz@sage.cgd.ucar.edu>, author of PGP, PGP Users' Guide, Volume 2. Phil stopped being openly involved with PGP distribution after being threatened with legal action by PKP.

``PKP can test the validity of its patent and recover its damages, if any, in a suit against the developers and distributors of PGP, if it cares to. [ ... ] It is virtually unheard-of to sue individual end-use consumers of allegedly infringing technology.''

- Eben Moglen <em21@cunixf.cc.columbia.edu>, Professor of Law & Legal History, Columbia University, archived in ftp.informatik.uni-hamburg.de:/pub/virus/misc/pgplegal.zip. Note that PKP has, in fact, threatened some developers and distributors who are within the reach of U.S. law; generally, some agreement has been reached without going to court. This is why, for example, few U.S. FTP sites are willing to carry PGP.

``Using PGP is like having a Morganti weapon; if "they" need a reason to give you a hassle, "they" have one. "They" can be the legal authorities, your sysadmin, or just someone who wants to make trouble for you. [ ... ] The tradeoffs should be considered.''

- Christopher Davis <ckd@eff.org>, System Manager & Postmaster, Electronic Frontier Foundation & Kapor Enterprises, Inc., id <CKD.93Mar18114533@loiosh.eff.org>. Some system administrators have instructed their users that using PGP on their systems is not permitted.

* Both PGP and RIPEM are export-restricted, and may not be lawfully sent outside the U.S. and Canada without an export license. However, PGP is already used and available internationally.

Whether you use PGP or RIPEM or whatever, the documentation to PGP is recommended reading to anyone interested in such issues. Unfortunately, it's difficult to find the documentation separate from the program.

I do not consider PGP and RIPEM to be in ``competition.'' The two programs were designed with different guidelines and priorities, and each does a reasonably decent job of doing what it was written to do. The authors and users of both programs generally share the goal of seeing widespread use of free cryptographic tools to enhance privacy and security. It is unfortunate that they cannot interoperate (yet).

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. It is rumored to be integrated into an existing mail user agent (MH) rather than a stand-alone system, and in beta test.

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

You may wish to check the companion post "ripem-attacks" which discusses some of the more obvious attacks on RIPEM's security and what procedures will minimize the risk. RIPEM's main "weak area" is probably key distribution.