Re: Matt Blaze: Paul Kocher's timing attack

["Angelos D. Keromytis" <kermit@soscorp.com>]

In message <199512110440.AA11632@interlock.ans.net>, "Perry E. Metzger" writes:
>
>The attack in question is quite general and probably works for both
>Photuris and SKIP -- both should be changed around in the light of
>Kocher's attack.
>
Most certainly works for both.
One solution (in Photuris at least) is to always wait until the closest x
second multiple (i'd say x = 5) after the exponentation has finished. So, if
exponentation starts at time Y and finishes at Y + 7, the packet should be
transmitted no sooner than Y + 10. Essentially, packet transmission delay
(the time between receiving an EXCHANGE_RESPONSE and sending an IDENTIFICATION)
should be independent from the actual exponentation time. Note that the attack
only works on the exchange mentioned above.
-Angelos

PS. The paper implies that the same attack can be pulled on symetric
cryptosystems as well, but no analysis is done.

---

References:

• Matt Blaze: Paul Kocher's timing attack
• From: "Perry E. Metzger" <perry@piermont.com>

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