Subject: [SIP] SIP gateways and authentication

From: "James A. Donald" <[email-masked]>
Date: Sat, 02 Sep 2000 09:51:32 -0700

--
From: Henry Sinnreich [mailto:[email-masked]]:
 > > Am not sure such complexity is jutified for phone calls having the
 > > cost close to e-mail.

At 10:10 AM 9/1/2000 -0500, Brian Stucker wrote:
 > Cheap or not, do you really want to start chipping away at the image
 > that people have that a phone call is ubiquitous, reliable, and
 > (relatively) secure transaction in their minds? It took decades > of
 > marketing and technical performance to get to that point, why not
 > try to maintain that in the future?

Possibly you understood Henry Sinnreich as referring to the computational 
cost of preventing offline dictionary attacks.

I understood him to be referring to the user experience.

The user experience should of course be unaffected by the defence against 
dictionary attack, if that defense is correctly implemented, but he is 
correct to claim there is a computational cost,

In the scheme I described, there is one public key operation per pair of 
entities interacting, per logon session, not several public key operations 
per interaction.

Several public key operations per interaction would indeed be an 
unacceptable expense.  One public key operation per pair of interacting 
entities per logon session, not per message, is unlikely to be a 
significant expense.

A single https web page takes many public key operations, typically eight 
to twelve per web page, and this has been a significant, but tolerable, 
barrier to the deployment of https.

To implement security at a cost similar to that of https would indeed be an 
unacceptable cost, because of the large number of very small interactions 
we expect.  The proposal I described was designed to minimize the cost of 
public key operations, to keep them to a level much lower than those of https.

     --digsig
          James A. Donald
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      F4BXeae+tmDuVH7AGWuWikXT20fqIq6Narhv2/0C
      4gHoCmYD2HS/uDHpSCaIQuLuU707H/TjqyEoPD2s1

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From: Stephen Thomas <[email-masked]>
Date: Wed, 20 Sep 2000 15:21:43 -0400

Relatively far from the topic, but it seemed worthwhile to clear up any 
potential misinformation.

At 12:51 PM 2000-09-02, James A. Donald wrote:
>to twelve per web page

This is simply not true. For the first Web page retrieved from a server, 
the client (browser) has to do at least one decryption to validate the 
server's certificate and one encryption to encrypt the session key. The 
server then has to do one decryption to recover the session key. (The 
client may have to do more than one decryption if it needs to validate 
multiple levels in a certificate hierarchy.) That's it, and once the 
session key has been exchanged, it can be used for subsequent pages (either 
through HTTP persistence or SSL session re-use).

Stephen

____________________________________________________________________
Stephen Thomas                                       +1 404 872 4887
TransNexus, Chief Technical Officer    [email-masked]