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RE: Some comments on Digest Auth

From: Paul Leach <paulle@microsoft.com>
Date: Tue, 20 Jan 1998 12:49:33 -0800
Message-Id: <5CEA8663F24DD111A96100805FFE6587203988@red-msg-51.dns.microsoft.com>
To: Yaron Goland <yarong@microsoft.com>, "'dmk@research.bell-labs.com'" <dmk@research.bell-labs.com>
Cc: http-wg@cuckoo.hpl.hp.com


> ----------
> From: 	dmk@research.bell-labs.com[SMTP:dmk@research.bell-labs.com]
> Sent: 	Monday, January 19, 1998 11:13 AM
> To: 	Yaron Goland
> Cc: 	http-wg@cuckoo.hpl.hp.com
> Subject: 	RE: Some comments on Digest Auth
> 
> Yaron Goland <yarong@microsoft.com> wrote:
> 
>   > ASSUMPTION: Avoiding replay attacks is important enough to most
> implementers
>   > that either the standard will require or implementers will voluntarily
>   > refuse to accept the same nonce twice.
>   > 
>   > GOAL OF THIS MESSAGE: To demonstrates that the current digest auth
>   > mechanism, from the point of view of performance in situations where
> we wish
>   > to prevent replay attacks, is unacceptably sub-optimal.
> 
> Ah, excellent that you set those forth, because I disagree with the
> assumption.
> 
> The purpose of Digest is to replace Basic, with its cleartext
> passwords.  Basic is already subject to replay attacks.  Digest should
> be no more susceptible, and it isn't more susceptible.  By clever
> choice of time-limited nonces, it can easily be less so.  But it isn't
> perfect.  We've known that for a long time.
> 
> So let me hark back to the discussion of a few weeks ago.  Let's not
> try to make Digest do something it was not intended to do.  Let's
> hold replay-proof Digest for digest-ng discussions.
> 
No.

A replayable Digest is just as bad as Basic.

Paul
Received on Wednesday, 21 January 1998 04:59:07 EST

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