From uri at watson.ibm.com Sat Jul 10 19:05:03 1993 From: uri at watson.ibm.com (uri at watson.ibm.com) Date: Sat, 10 Jul 93 19:05:03 PDT Subject: encrypted email software In-Reply-To: <9307100144.AA14701@toad.com> Message-ID: <9307110204.AA13167@buoy.watson.ibm.com> peter honeyman says: > > still around about why it was changed from 64 bit to 56 bit, > you mean 112 -> 56. this has been resolved -- it seems that longer keys > don't impose any additional complexity on des attacks. although these > attacks were discovered by the open crypto community only a few years ago, > nsa had these techniques in hand long before. the bottom line is that > additional key bits would not make des more secure. double des or triple > des do. Well, first - I believe DES was designed with 64 bit keys in mind, and then due to some technical (unspecified :-) reasons he key was shortened to 56 bits (and 56-bit version was submitted to NBS). While longer key indeed offers little protection against attacks like differential cryptanalysis - it's hard to argue that it can blow brute-force attack out of the water... And I'd be somewhat more concerned about an adversary cracking my DES-encrypted mail via brute force, than tapping my channel and collecting 2^45 of plaintext-ciphertext pairs to deduce my DES [randomly selected] key (:-). N'est pas? > it has long been believed that a dedicated des-cracker is within the budget > of extremely well financed organizations. Well, of course a government (any government :-) could build such a thing... After all, don't they get all those tax money? (:-) -- Regards, Uri uri at watson.ibm.com scifi!angmar!uri N2RIU -----------