Re: Questions about Version Negotiation Concerning Possible Handshake Interruption

[<[e-mail]>]

On 10/02/2018 10:00, Kazuho Oku wrote:
>> >  Alternatively, what about a "no fallback" mode for sensitive applications
>> >  like DNS ?
 >
> I agree that providing such an option would narrow the attack window.
> The other option is to let the client propose multiple versions and
> the server select one, as proposed in my previous mail.
>
> But even if we do that, there's still the chance of an attacker
> injecting a Handshake packet that contains a corrupt ServerHello
> message. In such case, the client would fail to complete the handshake
> with the server.

Yes, but this weakens the threat from outright intrusion to mere DOS, right ?

If so, note that the attacker may always follow its packet-of-death with a 
flood, making the receiver-side UDP socket overflow and eventually drop the 
legitimate server's response. In this case, not even a TLS context backup will 
be able to recover. Agreed, that's a heavier sword for a thicker shield, but 
that's doable ;)

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