Subject: Re: [SIP] Re: SIP gateways and authentication

From: "James A. Donald" <[email-masked]>
Date: Fri, 01 Sep 2000 08:25:00 -0700

--
At 09:59 AM 8/31/2000 -0700, Michael Thomas wrote:
 > It looks like your argument is not with the SIP WG but with the CAT
 > WG.

To be useful, encryption must be integral with a communications 
protocol.  To be secure, a communications protocol must be integral with 
encryption.

 > I'm sure a lot of folks there would be willing to entertain (or not)
 > this argument. In particular, the assertion that that Kerberos is
 > inherently subject to dictionary attacks looks more like an
 > indictment against symmetric key cryptography in general, rather
 > than Kerberos in particular.

There is nothing special about symmetric key cryptography that makes it 
particularly subject to dictionary attacks.  In all public key solutions, 
the public keys are used to set up a symmetric key that is not subject to 
dictionary attacks.

It is probably possible to set up a system with properties similar to those 
that I outlined using nothing but symmetric key cryptography, though it 
would be more complex, hence harder to understand and harder to get right.

Existing symmetric key solutions (Kerberos) are vulnerable to dictionary attack

Existing public key solutions are hard to use and unpopular.

These are properties of the particular implementations, and the particular 
tasks for which they are used, not a property of the underlying 
technology.   The technology is merely a tool.  It is what one makes with 
the tool that has particular properties, like being hard to use, or being 
vulnerable to particular attacks

     --digsig
          James A. Donald
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      xirSvfQvSQVFCs8dj58C5bSdC21fv2EaGyNzr8wn
      4x8kyGomth1BRtbAUDUQHnw3q8MGtTv7Mb395WWQ4

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---

From: Michael Thomas <[email-masked]>
Date: Fri, 1 Sep 2000 09:32:10 -0700 (PDT)

James A. Donald writes:
 > In all public key solutions, 

   False. A public key solution that chose bad
   symmetric keys would be subject to dictionary
   attacks and much more.

 > understand and harder to get right.

   FSVO "more".
 
 > Existing symmetric key solutions (Kerberos) are vulnerable to

   This is a ludicrous strawman. People choose
   dictionary attackable symmetric keys, not
   Kerberos. 

   Talk about babies and bathwater...

		Mike