Re: [TLS] New Cached info draft
Stefan Santesson <stefan@aaa-sec.com> Tue, 30 March 2010 18:10 UTC
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Date: Tue, 30 Mar 2010 20:08:46 +0100
From: Stefan Santesson <stefan@aaa-sec.com>
To: mrex@sap.com
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Thread-Topic: [TLS] New Cached info draft
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Cc: tls@ietf.org
Subject: Re: [TLS] New Cached info draft
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Martin, On 10-03-30 6:23 PM, "Martin Rex" <mrex@sap.com> wrote: > Stefan Santesson wrote: >> >> The most important reason being that the server need to reply with the same >> extension that the client sends, everything else is a violation of TLS. > > To me it sounded like Brian disliked the ServerHelloExtension > to be allowed empty on the initial discovery, rather than telling > the client for which handshake data the server supports caching. > > I do not think that he suggested to not return the extension _and_ > replace cached data. > I interpreted the ServerCachedInformation structure as a separate extension sent only by the server. > >> On 10-03-30 5:34 PM, "Brian Smith" <brian@briansmith.org> wrote: >> >>> * The draft says that CachedInformation.cached_info can be up to (2^16-1)*9 >>> = 590KB in size. extension_data can't be larger than 64KB, so the max bound >>> for the CachedInformation.cached_info array must be 7281 or less. But, >>> really, sending more than a few hashes per type of cached info is likely to >>> run into DoS countermeasures. It would be better to have the specification >>> require and/or at least recommend that there not be more than one (or at >>> most a few) hashes per information type in the client hello. > > To me, allowing the client to cache distinct values for the same > server leads to cache management problems. How should a client expire > outdated content from his cache? If the client only caches one item > per "server:port" pair, then expiring of outdated cached information > is a non-issue. > > It's a non-issue in any case. A timer for example works well. Nothing prevents the client to refuse caching more than one object per type and server, but that restriction doesn't strike me as necessary. >> >>> * The draft says "A present non-empty digest_value indicates that the server >>> will honor caching of objects of the specified type that matches the present >>> digest value." I don't see why this is necessary. The server should always >>> be supporting the digests of the values that it most recently returned, for >>> the information items it claims to support, so the semantics for empty >>> digest_values in the server extension are good enough. > > I would also appreciate semantics as suggested here. > Allow the server to return a ServerHelloExtension that explicitly list > the types of information for which the server supports caching, but > _without_ a digest_value, both on discovery and on actual use of > the caching extension by the client, so that the server does not > have to pre-calculate this data of future handshake message > while it is composing ServerHello. > The server doesn't have to send digest values in current draft. > > -Martin
- Re: [TLS] New Cached info draft Stefan Santesson
- Re: [TLS] New Cached info draft Stefan Santesson
- [TLS] New Cached info draft Stefan Santesson
- Re: [TLS] New Cached info draft Kemp, David P.
- Re: [TLS] New Cached info draft Adam Langley
- Re: [TLS] New Cached info draft Stefan Santesson
- Re: [TLS] New Cached info draft Stefan Santesson
- Re: [TLS] New Cached info draft Marsh Ray
- Re: [TLS] New Cached info draft Marsh Ray
- Re: [TLS] New Cached info draft Stefan Santesson
- Re: [TLS] New Cached info draft Stefan Santesson
- Re: [TLS] New Cached info draft Stefan Santesson
- Re: [TLS] New Cached info draft Simon Josefsson
- Re: [TLS] New Cached info draft Stefan Santesson
- Re: [TLS] New Cached info draft Adam Langley
- Re: [TLS] New Cached info draft Brian Smith
- Re: [TLS] New Cached info draft Brian Smith
- Re: [TLS] New Cached info draft Stefan Santesson
- Re: [TLS] New Cached info draft Martin Rex
- Re: [TLS] New Cached info draft Stefan Santesson
- Re: [TLS] New Cached info draft Brian Smith
- Re: [TLS] New Cached info draft Martin Rex
- Re: [TLS] New Cached info draft Stefan Santesson
- Re: [TLS] New Cached info draft Brian Smith
- Re: [TLS] New Cached info draft Stefan Santesson
- Re: [TLS] New Cached info draft Stefan Santesson
- Re: [TLS] New Cached info draft Michael D'Errico
- Re: [TLS] New Cached info draft Marsh Ray
- Re: [TLS] New Cached info draft Brian Smith
- Re: [TLS] New Cached info draft Adam Langley
- Re: [TLS] New Cached info draft Stefan Santesson
- Re: [TLS] New Cached info draft Martin Rex
- Re: [TLS] New Cached info draft Martin Rex
- Re: [TLS] New Cached info draft Marsh Ray
- Re: [TLS] New Cached info draft Martin Rex