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1994-05-20 - Re: D-H key exchange - how does it work?

Header Data

From: “Perry E. Metzger” <perry@imsi.com>
To: hughes@ah.com (Eric Hughes)
Message Hash: 1b567b416f6f4d4d717620eda719dcd4d9ddbeb32ac876afc019e1b5bdd35645
Message ID: <9405201659.AA07058@snark.imsi.com>
Reply To: <9405201655.AA11052@ah.com>
UTC Datetime: 1994-05-20 16:59:38 UTC
Raw Date: Fri, 20 May 94 09:59:38 PDT

Raw message

From: "Perry E. Metzger" <perry@imsi.com>
Date: Fri, 20 May 94 09:59:38 PDT
To: hughes@ah.com (Eric Hughes)
Subject: Re: D-H key exchange - how does it work?
In-Reply-To: <9405201655.AA11052@ah.com>
Message-ID: <9405201659.AA07058@snark.imsi.com>
MIME-Version: 1.0
Content-Type: text/plain



Eric Hughes says:
>    > In addition, changing the modulus can have unpleasant effects on
>    > traffic analysis, if not done properly.
> 
>    Of what sort?
> 
> For D-H, the modulus must be transmitted in the clear.  Unless you use
> a different modulus for each conversation, there is a persistency to
> the moduli that gives rise to a pseudo-identity.

You don't HAVE to transmit the modulus in the clear. Its often
worthwhile to use D-H for key exchange even if both sides know the
other's RSA public keys. Why? Because then the keys used for
conventional session encryption need not be compromised for historical
traffic even if the RSA keys are later compromised.

Perry

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