Re: [TLS] Connection ID Draft

[Matt Caswell <[e-mail]>]

On 17/10/17 22:35, Martin Thomson wrote:
> On Tue, Oct 17, 2017 at 9:26 PM, Fossati, Thomas (Nokia -
> GB/Cambridge, UK) <[e-mail]> wrote:
>> The following case (NAT box reboot) is problematic:
>>
>> 1. Application '1' on host A (A.1) uses DTLS+CID with application '1' on
>>    host B (B.1);
>> 2. Application '2' on host A (A.2) uses plain-old DTLS with B.1;
>> 3. The NAT box reboots (all previous 5-tuple mappings are lost);
>> 4. B.1 receives a record from A.1 (whose 5-tuple has changed in the
>>    meanwhile);
>>
>> How is B.1 supposed to correctly interpret the bytes starting at offset
>> +11?  (For what it knows, it could be CID from A.1 or the length field
>> from A.2.)
> 
> I don't think that this is a problem.
> 
> connection = five_tuples.lookup(packet.five_tuple)
> if (!connection) {
>   connection = connection_ids.lookup(packet[connection_id_offset:connection_id_offset+connection_id_length])
> }

Just skimming this old thread...doesn't this fail in the case where the
five tuple has been reused? In that case five_tuples.lookup will return
an old stale connection which the server thinks is still valid so we
never get to lookup the connection id. With an explicit marking we would
not fail in this scenario.

Matt