Re: [TLS] Cached-info substitution

Adam Langley <> Fri, 19 February 2010 16:51 UTC

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Date: Fri, 19 Feb 2010 11:52:58 -0500
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From: Adam Langley <>
To: Brian Smith <>
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Subject: Re: [TLS] Cached-info substitution
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On Fri, Feb 19, 2010 at 11:44 AM, Brian Smith <> wrote:
> I had been making the (apparently incorrect) assumption that only one
> CachedObject per CachedInformationType value was allowed in the client
> hello. I thought the intention here was to have the client always cache/send
> the value for each information type that was most recently received from the
> server (perhaps out-of-band). Is there a need for more flexibility than
> that? AFAICT, for the uses identified so far, there isn't.

I had interpreted the draft to mean that multiple possible
CachedObjects with the same type could be presented.

I can imagine some use cases where this would be helpful: an
organisation which can multiple serving clusters for the same domain
name, where each cluster has a different certificate. Or when a new
certificate was being rolled out to a number of servers, but clients
were getting load balanced between them.

However, given that this is only an optimisation, these cases might be
sufficiently unimportant that we can forbid multiple CachedObjects
with the same type and reap the benefits in a simpler substitution
scheme. I think I would be happy with that unless some particularly
compelling use case arises.