Re: SAFE Forum--some comments

["Mark M." <markm@voicenet.com>]

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On Wed, 3 Jul 1996, Bill Frantz wrote:

> I hear this as the server sends out a key which the client uses to encrypt
> the username/password.  This algorithm makes less sense than the one I
> thought I heard at the SAFE forum on Monday which was:

True.  That algorithm is completely useless.

> 
> (1) The server sends out a challenge/salt (different each time)
> (2) The client uses a secure hash to compute hash(salt||password) and
> returns the username and the hash.
> (3) The server computes hash(salt||password) and compares the hashes.
> 
> Given that there is still some interest in algorithms and protocols on this
> list, can you describe what is really happening?

That one makes more sense.  If the salt is completely random, then an attacker
will not be able to use a replay attack.  Since the password is hashed, there
is no way to find it out given the output.  This does require the server to
maintain a list of cleartext passwords, but that's not any worse then Kerberos
which requires a KDC store everyone's DES key.

- -- Mark

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