Re: DES Key Decryption Time
To: Ali Saifullah Khan <firstname.lastname@example.org> From: Valdis.Kletnieks@vt.edu Date: Wed, 09 Apr 2003 14:09:42 -0400
On Wed, 09 Apr 2003 22:17:42 +0500, Ali Saifullah Khan <email@example.com> said:
> What is the approx. number of clock cycles required to decrypt a 56-bit DES
> key / signature ?
In general, difficult to predict.
Assuming a really smart hardware implementation, you can probably get it
down to around 32 cycles (assuming a PAL to do the S-box and other stuff),
doing each of 16 rounds in 2 cycles. A really good software implementation
will need more, and a stupid implementation will require even more. (I'm
handwaving about key setup here...)
In addition, there's key initialization issues - very rarely is DES used to
encrypt only one block. So you usually take a big hit in setting up the
keys on the first block, and then subsequent blocks take a much smaller hit.
Also, note that "clock cycles" is *always* a total crock when trying to
compare across different architectures - the *SAME* instruction can take
a different number of cycles on a Pentium-4, a Pentium-3, a Crusoe chip - and
those are all the same software architecture. Comparing it to cycle count
on a MIPS or Power3 chipset would be a total loss. Then add in issues like
instruction parallelism and cache structure.....
- application/pgp-signature attachment: stored