Encryption keys: RSA vs. ElGamal

at120 at hushmail.com at120 at hushmail.com
Mon Nov 26 10:56:06 CET 2007


I need to create a subordinate key, which will be used for 
encryption only. I tried to find out how RSA differ from ElGamal by 
searching on the web, but I did not find much useful information. 
There are some pages that explain the algorithms in detail, but I'm 
not smart enough to evaluate their security and efficiency just by 
looking at the algorithms.

So it would be great if someone could tell me how they differ when 
it comes to security and efficiency. I know that "A disadvantage of 
the ElGamal system is that the encrypted message becomes very big, 
about twice the size of the original message", and that both seem 
to be limited to use no larger than 4096-bit keys, but that's all I 
know. Please don't give me "they're both secure enough" or "just 
use the defaults" type of answers, I want detailed information.

Are there any patent issues with ElGamal? The Wikipedia article 
mentions nothing about a patent. I found this: "Although the 
inventor, Taher Elgamal, did not apply for a patent on his 
invention, the owners of the Diffie-Hellman patent (US patent 
4,200,770) felt this system was covered by their patent".

I know that RSA was published in 1977, and the patent on it ran out 
in 2000. ElGamal is from 1984, so if there's a patent on it, will 
it expire/has it expired in 2007?


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