Re: Brute Force DES

[Kevin L Prigge <Kevin.L.Prigge-2@tc.umn.edu>]

Perry E. Metzger said:
> 
> "Peter Trei" writes:
> > The fastest general purpose, freely available des implementation I'm
> > aware of is libdes. by Eric Young. With this, I can do a set_key in 
> > 15.8 us, and an ecb_encrypt in 95 us/block. That adds up to 
> > about 9,000 keytests/sec (this is on a 90 MHz P5, running NT).
> 
> I'll point out that like most DES implementations, Eric's tries to
> spend a lot of time in key setup to save time later on in
> encryption/decryption. This tradeoff would probably be very different
> if you didn't plan on trying more than one or two blocks of decryption
> after getting a key.
> 

For instance if you had a DES encrypted gzipped file. The first 2 bytes
plaintext will be Ox1f8b. You'd only have to try to fully decrypt 
1 out of 65535 keys.

-- 
Kevin L. Prigge                     | "I rarely saw people sitting at
Systems Software Programmer         |  computers producing real code
Internet Enterprise - OIT           |  wearing ties." - Philippe Kahn
University of Minnesota             | (speech at Software Development '90)