Subject: [TLS] DTLS cookie and session resumption.

From: Fabrice Gautier <[email-masked]>
Date: Fri, 20 Dec 2013 10:25:16 -0800

Hi,

Is it safe for a DTLS server not to perform a cookie verification and
send a ClientHelloVerifyRequest message if the ClientHello sessionID
point to a session that can be resumed successfully ?

I'm assuming it's not in general. For example, an attacker could first
perform a full connection, then DDOS the server with resumption
attempts.

-- Fabrice

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From: Nikos Mavrogiannopoulos <[email-masked]>
Date: Mon, 23 Dec 2013 13:46:35 +0100

> perform a full connection, then DDOS the server with resumption

Or the attacker could sniff one session ID and then flood the server
using it.

regards,
Nikos

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From: Martin Thomson <[email-masked]>
Date: Mon, 23 Dec 2013 09:01:43 -0800

> perform a full connection, then DDOS the server with resumption

That's true in general, as Nikos points out.  That said, if you are
using something like ICE [RFC5245], this can be avoided by limiting
the number of DTLS connections to one for each remote ICE username
fragment.