RFR 8211018: Session Resumption without Server-Side State

[Jamil Nimeh]

I think we're overstating the "otherwise" case.  A client that uses this 
strict 4507 format would initially send a ticket that looks like { 00 23 
00 02 00 00 } to which our server would reject this extension (since the 
final 00 00 would be interpreted as a ticket when the client did not 
intend it to be so).  The result of this SHOULD be that the server 
responds with a ServerHello that doesn't have the SessionTicket extension.

That doesn't mean that resumption cannot happen.  It just means that 
resumption happens using the usual session ID lookup approach and the 
server is caching the session rather than letting the client do the 
work.  Given that this is a degenerate case for what (I hope) is a small 
subset of older clients, I think using server-cached sessions is OK.

I don't believe we should ever find ourselves in a case where the 
strict-4507 client actually gets a real ticket from our server, and in 
turn should never hand us a ticket thinking that resumption could 
actually take place via said ticket.

On the client side, we cannot know ahead of time that the server is 
strict-4057, so we have to send a 5077 style SessionTicket extension.  
The server will probably not like that and not assert SessionTicket in 
its server hello.  So our client should fall back to using the session 
ID to support resumption, and the server should follow suit by caching 
the session.

--Jamil

On 6/5/2019 2:28 PM, Xuelei Fan wrote:
> I don’t know if there are any deployment of RFC 4507.  If not, we are safe; otherwise there are interop problems for session resumption.
>
> Xuelei
>
>> On Jun 5, 2019, at 2:19 PM, Jamil Nimeh <jamil.j.nimeh at oracle.com> wrote:
>>
>> Hi Xuelei,
>>
>> Given that 4507 is obsoleted in favor of 5077 is there really that much value to supporting this older/broken extension format?  Do we know of clients that still adhere to 4507?  Otherwise it seems better to stick to 5077 and the approach in TLS 1.3 and not try to go back and support an earlier obsoleted approach to this feature.
>>> These lines took me to the cooperation behaviors between RFC 5077 and RFC 4507.  It looks like we don't support RFC 4507 format of SessionTicket extension.  As RFC 5077 and RFC 4507 use the same extension ID for different extension format.  There are potential compatibility issues, and make session resumption impossible.  I would like to have a workaround to accept both formats.  For example, using the a cookie at the beginning of the ticket, as described in appendix-A of RFC 5077.
>>>
>>>
>>> I will review the rest of this class in the afternoon or tomorrow.
>>>
>>> Thanks,
>>> Xuelei
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