RE: Authentication Mechanism Matrix (was L2TP vs IPSEC)

[David Jablon <dpj@xxxxxxxxxxxxx>]

Some banter on what kind of authentication method can handle a
small legacy-style shared secret password ...

At 04:44 PM 6/21/00 -0700, CHINNA N.R. PELLACURU wrote:
> [IKE (?)] probably wasn't designed, but to make it secure in this scenario is
> just a matter of implementation (IE. no change to bits on the wire).

Guess again.  My secret is "HRW#54".  That's all I can remember.
I dare you to show me how to use IKE securely with this as the secret key.

... then a diversion into smart-card-enabled kiosks ...

CHINNA:
>Let's assume that, before I stick my smartcard into the machine, I make
>sure that all the software running on the machine is cryptographically
>singed by the vendor [...] and I 
>can verify the signature, and thus make sure that there are no trojan
>software in there. ... 

David:
Amusing, but still irrelevant.

How do you get the SHA-1 hash of the software?
Were you thinking of just asking the software to hand it over?
What if it hands you the signed hash that was computed before the BIG
EVIL PATCH?  As you should guess, I'm not looking for an answer.

... and finally, a "definition" ...

David:
>> Public/private keys and IKE shared secret authentication work just fine
>> with large secret keys.  But for passwords, you need to use either:
>> 
>> 	(1) an authenticated tunnel secured by *something else*,
>> or
>> 	(2) a zero-knowledge password method which tolerates small keys directly.
>> 
>> Or better still, use both. :-)

CHINNA:
>And so what is your cryptographic definition of "user authentication" Vs
>"machine authentication". I don't think you have provided any.

Fine.  Here's my formal definition:

	User authentication needs a secret.
	Machines can remember big ones,
	but people can't.
	Deal with it.

OK, so it's not formal, and not exactly Haiku, but it gets to the point.

---------------------------------------------------
David P. Jablon
Integrity Sciences, Inc.
dpj@xxxxxxxxxxxxxxxxxxxxx
www.IntegritySciences.com