Re: [TLS] WGLC for draft-ietf-tls-cross-sni-resumption

Martin Thomson <> Tue, 10 August 2021 02:39 UTC

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Date: Tue, 10 Aug 2021 12:38:21 +1000
From: "Martin Thomson" <>
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Subject: Re: [TLS] WGLC for draft-ietf-tls-cross-sni-resumption
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This document is mostly fine.

The text on use of client certificates isn't particularly clear.  The key piece of information that a reader is going to need is that a resumed connection will include any (and potentially all) client authentication.

I found the meat of the flag definition hard to follow.  There is a lot of 2119 language, but very little of it relates to the operation of this extension.  Some is just restatement of RFC 8446, which comes with real risks and should be avoided.  I think that what this needs to say is:

1. What the protocol mechanism is: (a flag in NST)
2. What sending that signal means.  For example, "The flag is an assertion from the server that all servers that answer to the names in the certificate are able to use this ticket."
3. What the client might do with that.  For example, "If a client would accept the certificate for a new connection, it can/MAY attempt resumption even if the server name differs from the server name of the original connection." <- that might be the only 2119 language you need in the entire document, though I'm not sure you even need that.

Then talk about consequences (this is currently in Security Considerations and is mostly good, though not all of this belongs in a section with that title):

1. What if the server is wrong in its assertion.   For example, "A server that wrongly advertises this flag could cause clients to waste tickets on connection attempts where resumption will not be successful."
2. Why the server might choose not to do this: need to coordinate across a deployment, it could be wrong, certificate bloat, key compromise scope, etc... (the existing text on this is fine)
3. What the client needs to consider before exercising this option (tracking -> partitioning, client authn)

On Sat, Jul 17, 2021, at 09:55, Christopher Wood wrote:
> This is the working group last call for the "Transport Layer Security 
> (TLS) Resumption across Server Names" draft, available here:
> Please review this document and send your comments to the list by July 
> 30, 2021. The GitHub repository for this draft is available here:
> Thanks,
> Chris, on behalf of the chairs
> _______________________________________________
> TLS mailing list