Re: [TLS] First TLS cached information draft posted
Simon Josefsson <simon@josefsson.org> Tue, 09 June 2009 13:41 UTC
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From: Simon Josefsson <simon@josefsson.org>
To: martin.rex@sap.com
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Date: Tue, 09 Jun 2009 15:41:27 +0200
In-Reply-To: <200906091223.n59CNqov028494@fs4113.wdf.sap.corp> (Martin Rex's message of "Tue, 9 Jun 2009 14:23:52 +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: >> >> Martin Rex <Martin.Rex@sap.com> writes: >> >> >Simon Josefsson wrote: >> >> >> >> Good point, but how would a client know whether a server replaced the >> >> cached information with a hash or not if there is no signaling whether >> >> this happened or not? >> > >> > The client knows which Hash it would find, if the server would sent >> > the hash, so it could check for that. Even a collision of the >> > hash and the original handshake data would not cause a problem >> > with this "heuristical" determination. >> > >> > I'm wondering about the following: we should give a strong recommendation >> > about the minimum size of an object in order for caching to make any >> > sense at all, like >= 2x the size of the hash. >> > >> > Maybe the minimum size should be rather 3x hash size, considering >> > the rest of the protocol overhead. >> >> This seems like a good idea -- and it solves the problem in the client >> to identify whether the server replaced the data or not. If the minimum >> size is 3x hash size, the client can look at the length of the data. If >> it is longer than 3x hash size, it knows the server opted out from >> sending the hash. If it is shorter than 3x hash size, it knows the >> server actually did replace the data with a hash value. > > 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. /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