- cypherpunks-legacy@lists.ogf.org

Re: Diffie Hellman
by smb＠research.att.com 17 Jul '93

17 Jul '93

What is the best reference to the Diffie Hellman key exchange algorithm? (Preferably on line) Thanks Any decent book on cryptography should explain it. The idea was originally proposed in @article{Diffie76, author = {Whitfield Diffie and Martin E. Hellman}, journal = {IEEE Transactions on Information Theory}, month = {November}, pages = {644--654}, title = {New Directions in Cryptography}, volume = {IT-11}, year = {1976} } The basic idea is simple. Pick a large number p (probably a prime), and a base b that is a generator of the group of integers modulo p. Now, it turns out that given a known p, b, and (b^x) mod p, it's extremely hard to find out x. That's known as the discrete log problem. Here's how to use it. Let two parties, X and Y, pick random numbers x and y, 1 < x,y < p. They each calculate (b^x) mod p and (b^y) mod p and transmit them to each other. Now, X knows x and (b^y) mod p, so s/he can calculate (b^y)^x mod p = (b^(xy)) mod p. Y can do the same calculation. Now they both know (b^(xy)) mod p. But eavesdroppers know only (b^x) mod p and (b^y) mod p, and can't use those quantities to recover the shared secret. Typically, of course, X and Y will use that shared secret as a key to a conventional cryptosystem. The biggest problem with the algorithm, as outlined above, is that there is no authentication. An attacker can sit in the middle and speak that protocol to each legitimate party. One last point -- you can treat x as a secret key, and publish (b^X) mod p as a public key. Proof is left as an exercise for the reader. --Steve Bellovin

1 0

Diffie Hellman
by norm＠netcom.com 17 Jul '93

17 Jul '93

What is the best reference to the Diffie Hellman key exchange algorithm? (Preferably on line) Thanks

1 0

No Subject
by Karl Barrus 17 Jul '93

17 Jul '93

-----BEGIN PGP SIGNED MESSAGE----- This is a touchy topic! It's a tough call, since statements like: > in the UK. I am dismayed that this type of activity is being condoned > by an American Governmental Agency. I can only hope that this operation > is shut down and the responsible parties are reprimanded. I am > extremely disturbed by the thought that my tax money is being used for, > what I consider, unethical, immoral and possibly illegal activities. may be applied to MANY goverment activities: * foreign policy (Iraq, Vietnam, Contras, lots of others) * funding & the NEA * environmentalist concerns * homosexuals * gambling - lots of debate here in TX about the state lottery. Some found it unethical and immoral. Same goes for the greyhound racetrack near Houston. In the end, $$$$$$ won. * our favorite: cryptography > My main concern is that this instance of valid utilization of > "whistleblowing" has been overshadowed by the ravings of virus I'll have to say, though I disagree with your virus position and am saddened by the outcome, I don't see anything wrong with "whistleblowing" in this manner. > Perhaps the remainder of the net is not quite ready to acknowledge > anonymity? As I stated above, I'd really like to hear some of your This seem true. Just a few months ago there was an enormous flap over Julf's anonymous server. But then, like now, the issue was really over statements made and actions taken anonymously. However, anonymity became the focal point. /-----------------------------------\ | Karl L. Barrus | | elee9sf(a)menudo.uh.edu | <- preferred address | barrus(a)tree.egr.uh.edu (NeXTMail) | \-----------------------------------/ -----BEGIN PGP SIGNATURE----- Version: 2.3 iQCVAgUBLEgueYOA7OpLWtYzAQHdaQP/QEnqtm02Hkln0Mse2YccNxqcgB8v+aox 0VlZJDunfQeukSRgpVqMuAIvXPp9LPQGCr/ubAT01gxANtlSUpiVzMkfqDkxJm/b z/W1wKOogNrmWHqpR7GMkjPAVHDgRWG8iRtrpW186HKe+TcH8EH9lVmyYBtYGn78 UIjhYwqSLT4= =FIHB -----END PGP SIGNATURE-----

1 0

subscribe
by baumbach＠atmel.com 17 Jul '93

17 Jul '93

Sorry to send this to the list. (Is it still here?) I would like to resubscribe to cypherpunks, but cannot get a response from cypherpunks-request(a)toad.com . Any help is appreciated, Peter Baumbach baumbach(a)atmel.com ps. Could someone tell me if this reached the list?

1 0

Re: Crypto Conference from Hell
by L. Detweiler 17 Jul '93

17 Jul '93

Dr. David P. Maher, Chief Scientist for AT&T Secure Communications Systems, AT&T >As broadcast and multiple access >technologies are used increasingly for information transmission, and >everyday business is carried out in "cyberspace," structures that >ensure privacy, authenticity, and (often) anonymity must become part >of the natural landscape. wow, is this guy a cypherpunk? Gad, this is really mainstream. NYT, Newsweek, SciAm, and now a cryptographic conference *with* the NSA! We've hit the big time. (Oops, he's from AT&T.) >Wednesday, August 4, 1993 > >8:30-10:30 >CRYPTOGRAPHY POLICY IN THE U.S. YIKES, the fireworks are going to fly at this one. CSSPAB (NIST), EFF, NSA, FBI, SPA all in the same room at the same time. I sure hope there'll be transcripts of this one. It would sure beat all that Congressional testimony by far for rancor per bit! Cryptography meeting of the year?

1 0

Re: Names and Reputations
by norm＠netcom.com 17 Jul '93

17 Jul '93

J. Michael Diehl writes: > This is a good point, but I believe that eventually, people will want to sign > legal documents via pgp and such. So being able to tie a pseudonym to a > reputation to a public key to a REAL LIVE PERSON is very important. I think That is a good point too. Perhaps the laws and practices of Notary Publics may serve for one degree of assurance. They commonly need to know who is asking them to notarize something such as a will. I don't remember how they do this. I suppose that a Notary public should have a published public key that she uses like her seal.

1 0

Names and Reputations
by norm＠netcom.com 17 Jul '93

17 Jul '93

J. Michael Diehl wrote: I'm having a philosophical problem regarding when to sign someone else's public key. It strikes me that while a public key may be properly associated with someone that you know by sight it may more generally be associated with an abstract reputation. Connecting a face to a public key may be less useful than connecting a public key with someone that I recognize by reputation. I don't know Stephen Wolff by sight but I do know him by reputation and have conversed with him by e-mail. If during these conversations we had exchanged public keys, even thru insecure channels, then that would be more reliable than exchanging keys with someone that I met in person who claimed to be Steve Wolff but with whom I did not have time to converse. Steve's reputation with me arose thru a book he wrote. If he had included his private key there it would be better yet. (Public keys had not been invented then.) Having been influenced by Steve's book I would be inclined to accept Steve's opinions in related areas, if they were signed by his private key. I need not know what Steve looks like! In CyberSpace it ultimately seems that the public key supplants ordinary names and all reputations are connected to public keys!

2 1

Re: steganography
by wcs＠anchor.ho.att.com 17 Jul '93

17 Jul '93

I think Kragen's definition of "Steganographically Strong" is a bit overstrong. He suggests that the cyphertext should not be recognizeable by its own program, with no checksums or program-specific delimiters, headers, etc. If checksums become widely used in other data formats (e.g. MIME or whatever), having them used in "innocent-looking-format" is ok. And having a checksum that only checks out if you have the correct key for decrypting the file is relatively ok, assuming you use strong encryption; it's really no more of a giveaway than having the correctly-decrypted plaintext have other recognizeable format, such as all-ascii or MIME or GIF. The request for a feature that corrupted files decrypt to total garbage and not just partial garbage can be implemented using some variant on doubly encrypting the file, e.g. descbc file | reverse-the-file | descbc. Most encryption systems can be used in modes that only trash the corrupted block, modes that trash the corrupted block and all following blocks, or modes that trash the corrupted block and some stuff after it, but eventually resync. The latter are useful for on-line continuous encryption systems like ethernet or T1 encryptors, where you don't want to send out guys with briefcases handcuffed to their arms any time there's a noise burst :-) One wimpy steganography approach I've thought of recently is to use uuencode. Each line starts with an indicator of how many characters are on the line, normally "M" for 64, followed by the characters; you could use variable-length lines with the length encoding your real (cyphertext) data at 6 bits/line. It'd be ugly, and probably noticeable, but you could always demonstrate that it outputs normal genuinely-innocent stuff by running it through uudecode. And it's only a factor of 10 less efficient than hiding it in a GIF! Bill Stewart

1 0

Re: Anonymity takes one on the chin
by peter honeyman 17 Jul '93

17 Jul '93

paul, my thoughts in (extremely) brief: i applaud your resolve to correct what you saw to be wrongdoing. i totally disagree with you on the merits of the case; i think the civil servant runing the bbs (i forget her name) provides a valuable service, and serves the common good. as usual, anonymity is a lightning rod here, although it is largely peripheral to the real issues. peter

1 0

Re: Relation between number theory and cryptography
by collins＠newton.apple.com 17 Jul '93

17 Jul '93

J. Michael Diehl <mdiehl(a)triton.unm.edu> writes: >if we were to add some noise [then] we have added [...] information Perhaps in 'Information Relativity'. With respect to the original system (and by definition), noise is not information. It is only data. Scott Collins | "Few people realize what tremendous power there | is in one of these things." -- Willy Wonka ......................|................................................ BUSINESS. voice:408.862.0540 fax:974.6094 collins(a)newton.apple.com Apple Computer, Inc. 1 Infinite Loop, MS 301-2C Cupertino, CA 95014 ....................................................................... PERSONAL. voice/fax:408.257.1746 catalyst(a)netcom.com ....................................................................... QUOTING. Full text of sources upon request. You may quote if you do the same *and* include this notice so your readers may quote similarly.

2 1