From eichin@cygnus.com Sun Mar 15 09:45:35 1992
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Date: Sun, 15 Mar 92 07:39:34 EST
From: "Mark W. Eichin" <eichin@cygnus.com>
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To: eichin@MIT.EDU
Subject: [smb@ulysses.att.com: Re: encryption]
SUB: [smb@ulysses.att.com: Re: encryption]
SUM: "Mark W. Eichin" <eichin@cygnus.com>->eichin

good bib refs

To: Cryptography-Digest@news-digests.mit.edu
From: smb@ulysses.att.com (Steven Bellovin)
Crossposted-To: alt.security
Subject: Re: encryption
Date: 14 Mar 92 17:37:12 GMT
SUB: Re: encryption
SUM: smb@ulysses.att.com (Steven Bellovin)->Cryptography-Digest@news-digests.mit.edu

In article <1992Mar14.134724.1753@bohemia.metronet.org>, Inelson@bohemia.metronet.org (Ian Nelson) writes:
> 
> Does anyonw know anything about "ELG" or ElGalal encryption?  Are there any
> programs which support it?  I read that it was a public encryption technique
> that used logs instead of prime numbers like RSA.  How would this compare to 
> RSA?  Since the government is behind it, I would think that it would be flawed.

Your paranoia is showing...

Anyway,you're apparently thinking of ElGamal's algorithms, described in

@article{elgamal,
   author = {Taher {ElGamal}},
   journal = {IEEE Transactions on Information Theory},
   month = {July},
   pages = {469--472},
   title = {A Public Key Cryptosystem and a Signature Scheme Based on Discrete L
ogarithms},
   volume = {IT-31},
   year = {1985}
}

They're based on the difficulty of finding discrete logarithms, not
regular ones.  If used correctly -- i.e., picking really good random
numbers during the encryption -- they're believed to be quite secure.  See

@article{nfscrack,
   author = {Brian A. LaMacchia and Andrew M. Odlyzko},
   journal = {Designs, Codes, and Cryptography},
   pages = {46--62},
   title = {Computation of Discrete Logarithms in Prime Fields},
   volume = {1},
   year = {1991},
}

for guidance on the difficulty of solving discrete logs.

Use of this algorithm may infringe on the Diffie-Hellman patent.  Consult
your own attorney for guidance.

RSA Data Security prefers RSA.  When the government proposed use of
a variation of ElGamal's signature scheme (actually, it's a variation
on Schnorr's scheme, I believe), they explained why they thought RSA
was superior.  Check back issues of comp.risks (on csl.sri.com) for
that discussion.

Followups to sci.crypt, please.