From: uri@watson.ibm.com
Date: Sat, 10 Jul 93 19:05:03 PDT
To: honey@citi.umich.edu (peter honeyman)
Subject: Re: encrypted email software
In-Reply-To: <9307100144.AA14701@toad.com>
Message-ID: <9307110204.AA13167@buoy.watson.ibm.com>
MIME-Version: 1.0
Content-Type: text/plain


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@watson.ibm.com      scifi!angmar!uri 	N2RIU
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