Re: [TLS] First TLS cached information draft posted
Simon Josefsson <simon@josefsson.org> Tue, 09 June 2009 14:00 UTC
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From: Simon Josefsson <simon@josefsson.org>
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Date: Tue, 09 Jun 2009 16:00:21 +0200
In-Reply-To: <200906091352.n59DqX3N004203@fs4113.wdf.sap.corp> (Martin Rex's message of "Tue, 9 Jun 2009 15:52:33 +0200 (MEST)")
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Cc: TLS@ietf.org
Subject: Re: [TLS] First TLS cached information draft posted
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Martin Rex <Martin.Rex@sap.com> writes: > Simon Josefsson wrote: >> > >> > Not quite. >> > >> > The caching extension is supposed to be generic, and the to-be-cached >> > real data may in some situations be quite short or even the same size >> > than the hash value (probably not for the server certificate caching, >> > but maybe for the list of certification authorities in the certificate >> > request message, which consists of distinguished names only, and >> > there could be just one very short DName (or none at all with TLS v1.1+) >> >> Then why use the extension? The point of the extension, as I understood >> it, is to replace large data with a small hash of the same data. If the >> data is small, the extension doesn't serve any purpose and should not be >> used. That is why I liked your suggestion to limit the use of the >> extension when the data is larger than 3x hash size. > > Look at this: > > Server supports caching of certificate_authorities list and runs with > a large list > > Client connects, caches the long list and announces the hash of the > cached information on future reconnects > > Server configuration is updated, certificate_authorities list > is cut down and now only contains one very short name. > > Client connects again (having still cached the previous long list), > server indicates to support caching of that value in principle, > but returns the real data since the hash proposed by the client > no longer matches. > > Client should now realize that the short data is the new real > data, should probably drop the cached value, and refrain from > further caching of the short value. Right. That is how I think it should work as well. I believe that adding a limit of 4x hash size (or similar) is still useful, though, since it would be pointless for the client in your example to update its cached hash with a hash of the new string, and send that hash in the future. Doing so would result in a handshake that is potentially _larger_ than if the cached data were sent. /Simon
- Re: [TLS] First TLS cached information draft post… Stefan Santesson
- Re: [TLS] First TLS cached information draft post… Simon Josefsson
- Re: [TLS] First TLS cached information draft post… Stefan Santesson
- Re: [TLS] First TLS cached information draft post… Martin Rex
- [TLS] First TLS cached information draft posted Stefan Santesson
- Re: [TLS] First TLS cached information draft post… Simon Josefsson
- Re: [TLS] First TLS cached information draft post… Stefan Santesson
- Re: [TLS] First TLS cached information draft post… Stefan Santesson
- Re: [TLS] First TLS cached information draft post… Simon Josefsson
- Re: [TLS] First TLS cached information draft post… Simon Josefsson
- Re: [TLS] First TLS cached information draft post… Simon Josefsson
- Re: [TLS] First TLS cached information draft post… Simon Josefsson
- Re: [TLS] First TLS cached information draft post… Martin Rex
- Re: [TLS] First TLS cached information draft post… Simon Josefsson
- Re: [TLS] First TLS cached information draft post… Martin Rex
- Re: [TLS] First TLS cached information draft post… Simon Josefsson
- Re: [TLS] First TLS cached information draft post… Martin Rex
- Re: [TLS] First TLS cached information draft post… Martin Rex
- Re: [TLS] First TLS cached information draft post… Simon Josefsson
- Re: [TLS] First TLS cached information draft post… Simon Josefsson
- Re: [TLS] First TLS cached information draft post… Simon Josefsson
- Re: [TLS] First TLS cached information draft post… Min Huang
- Re: [TLS] First TLS cached information draft post… Min Huang
- Re: [TLS] First TLS cached information draft post… Simon Josefsson
- Re: [TLS] First TLS cached information draft post… Martin Rex
- Re: [TLS] First TLS cached information draft post… Simon Josefsson
- Re: [TLS] First TLS cached information draft post… Stefan Santesson
- Re: [TLS] First TLS cached information draft post… Stefan Santesson
- Re: [TLS] First TLS cached information draft post… Stefan Santesson
- Re: [TLS] First TLS cached information draft post… Stefan Santesson
- Re: [TLS] First TLS cached information draft post… Martin Rex
- Re: [TLS] First TLS cached information draft post… Martin Rex
- Re: [TLS] First TLS cached information draft post… Stefan Santesson
- Re: [TLS] First TLS cached information draft post… Stefan Santesson