On Apr 24, 2009, at 7:50 AM, Robert J. Hansen wrote:
allen.schu...@gmail.com wrote:
What is the difference between DH/DSS and ElGamel/DSS? I was
reading up
on S/MIME v3 and PGP/MIME differences when that came up.
I don't know how it's used in the S/MIME standard. However, the
Elgamal
encryption algorithm is often misnamed the Diffie-Hellman encryption
algorithm.
The DH key exchange algorithm (DHKEA) came first, way back in the
'70s.
Then an Egyptian-American named Taher Elgamal did some groundbreaking
work in generalizing DHKEA, discovering the mathematical roots of
why it
worked as well as it does, and in the process developed a whole family
of algorithms. This family is often called the "Elgamal family." He
also developed the Elgamal encryption and signing algorithms.
It is my understanding that the correct name for what OpenPGP uses is
the Elgamal encryption algorithm. I don't know why PGP Corporation
calls it Diffie-Hellman encryption; it seems to be an idiosyncratic
usage.
It's historical. Back in the late 1990s, the PGP developers were
offered a free patent license if they called it Diffie-Hellman. Now
that the patent has expired, though, it's a little hard to change
their product without confusing a bunch of customers who would see
their "Diffie-Hellman" keys suddenly become "Elgamal" keys.
David
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