Re: [TLS] Wrapping up cached info
"Joseph Salowey (jsalowey)" <jsalowey@cisco.com> Wed, 19 May 2010 14:20 UTC
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Date: Wed, 19 May 2010 07:19:00 -0700
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Thread-Topic: [TLS] Wrapping up cached info
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From: "Joseph Salowey (jsalowey)" <jsalowey@cisco.com>
To: Stefan Santesson <stefan@aaa-sec.com>, mrex@sap.com
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Cc: tls@ietf.org
Subject: Re: [TLS] Wrapping up cached info
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Hi Stefan, To me this sounds like a good approach. I have some questions on whether the hash chosen is dependent upon the cipher suite used below. > -----Original Message----- > From: Stefan Santesson [mailto:stefan@aaa-sec.com] > Sent: Wednesday, May 19, 2010 6:43 AM > To: Stefan Santesson; mrex@sap.com; Joseph Salowey (jsalowey) > Cc: tls@ietf.org > Subject: Re: [TLS] Wrapping up cached info > > Not sure how I should interpret the silence? > > I guess it means that everyone agrees with me :) > > To repeat in short. Here is what I suggest based on the latest traffic: > > 1) A client, caching information also caches what hash algorithm was used > to > calculate the finished message at the time of caching. > [Joe] Will this be the same as the hash function used in the PRF of the cipher suite? It seems that using the same hash might make security analysis a little easier. > 2) On repeated connections, the client indicate cached info by sending a > hash of the cached object using the cached hash algorithm. (No use of FNV > hash) > > 3) The server accepts by returning the received hash instead of the cached > data. > [Joe] In the event that a different cipher suite is used with a different hash would the cached hash still be valid? > 4) The only hash agility provided is that the client will send a hash > algorithm identifier with the hash. > [Joe] This seems sufficient. > 5) The client MUST NOT send more than one hash per cached object, and MUST > used the cached hash algorithm. > > > This solves all issues raised (securely binds the cached data to the > finished calculation) and removes the need for hash agility > Syntactically it just requires adding a hash identifier and adjusting the > vector length for hash data. > > So I basically wander: > - Would this be acceptable? > - Who could NOT live with this solution? > - Who think it is worth the effort to agree on a better solution, and why? > > Regards > > > > > On 10-05-18 12:24 AM, "Stefan Santesson" <stefan@aaa-sec.com> wrote: > > > As Martin pointed out to me privately, the hash used in the finished > > calculation becomes known to the client only after receiving the serer > > hello. > > > > It would therefore be natural for the client to use the hash function > used > > to calculate the finished message at the time when the data was cached. > > > > The client would then indicate which hash algorithm it used and upon > > acceptance, the server will honor the request. > > > > /Stefan > > > > > > On 10-05-17 10:34 PM, "Stefan Santesson" <stefan@aaa-sec.com> wrote: > > > >> Guys, > >> > >> Where I come from we have a say "don't cross the river to get to the > water". > >> And to me this proposal to change the finished calculation is just > that. > >> > >> Look at it. > >> > >> The proposal is to bind the cached data by adding a hash of the cached > data > >> to the finished calculation. > >> > >> The proposal is further to avoid hash agility by picking the hash > algorithm > >> used by TLS's Finished message computation. > >> > >> > >> Now there are two ways to achieve this goal. > >> > >> 1) The crossing the river to get water approach: Exchange FNV hashes > of the > >> cached data in the handshake protocol exchange and then inject hashes > of the > >> same data into the finished calculation through an alteration of the > TLS > >> protocol. > >> > >> > >> 2) The simple approach: Use the hash algorithm of the finished > calculation > >> to hash the cached data (according to the current draft). > >> > >> > >> Alternative 2 securely bind the hashed data into the finished message > >> calculation without altering the algorithm. > >> > >> Alternative 2 requires at most a hash algorithm identifier added to the > >> protocol, if at all. We don't need to add negotiation since we always > use > >> the hash of the finished message calculation. Adding this identifier > would > >> be the only change made to the current draft. > >> > >> Alternative 2 don't require additional security analysis. If the hash > used > >> to calculate the finished message is broken, then we are screwed > anyway. > >> > >> /Stefan > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> On 10-05-17 9:16 PM, "Martin Rex" <mrex@sap.com> wrote: > >> > >>> Joseph Salowey wrote: > >>>> > >>>> I agree with Uri, that if you determine you need SHA-256 then you > should > >>>> plan for hash agility. TLS 1.2 plans for hash agility. > >>>> > >>>> What about Nico's proposal where a checksum is used to identify the > >>>> cached data and the actual handshake contains the actual data hashed > >>>> with the algorithm used in the PRF negotiated with the cipher suite? > >>>> > >>>> This way we don't have to introduce hash agility into the extension, > but > >>>> we have cryptographic hash agility where it matters in the Finished > >>>> computation. Does it solve the problem? > >>> > >>> Yes, I think so. > >>> This approach should solve the issue at the technical level. > >>> > >>> Going more into detail, one would hash/mac only the data that got > >>> actually replaced in the handshake, each prefixed by a (locally > computed) > >>> length field. > >>> > >>> -Martin > >>> _______________________________________________ > >>> TLS mailing list > >>> TLS@ietf.org > >>> https://www.ietf.org/mailman/listinfo/tls > >> > >> > >> _______________________________________________ > >> TLS mailing list > >> TLS@ietf.org > >> https://www.ietf.org/mailman/listinfo/tls > > > > >
- Re: [TLS] Wrapping up cached info Blumenthal, Uri - 0668 - MITLL
- [TLS] Consensus Call: FNV vs SHA1 Joseph Salowey (jsalowey)
- Re: [TLS] Consensus Call: FNV vs SHA1 Simon Josefsson
- Re: [TLS] Consensus Call: FNV vs SHA1 Blumenthal, Uri - 0668 - MITLL
- Re: [TLS] Consensus Call: FNV vs SHA1 Adam Langley
- Re: [TLS] Consensus Call: FNV vs SHA1 Marsh Ray
- Re: [TLS] Consensus Call: FNV vs SHA1 Robert Dugal
- Re: [TLS] Consensus Call: FNV vs SHA1 Stefan Santesson
- Re: [TLS] Consensus Call: FNV vs SHA1 Nicolas Williams
- Re: [TLS] Consensus Call: FNV vs SHA1 Stefan Santesson
- Re: [TLS] Consensus Call: FNV vs SHA1 Martin Rex
- Re: [TLS] Consensus Call: FNV vs SHA1 Jeffrey A. Williams
- Re: [TLS] Consensus Call: FNV vs SHA1 Paul Hoffman
- [TLS] Collisions (Re: Consensus Call: FNV vs SHA1) Nicolas Williams
- [TLS] Nico's suggestions - Re: Consensus Call: FN… Stefan Santesson
- Re: [TLS] Collisions (Re: Consensus Call: FNV vs … Blumenthal, Uri - 0668 - MITLL
- [TLS] Collisions (Re: Nico's suggestions - Re: Co… Nicolas Williams
- Re: [TLS] Collisions (Re: Consensus Call: FNV vs … Nicolas Williams
- Re: [TLS] Consensus Call: FNV vs SHA1 Simon Josefsson
- [TLS] Collisions (Re: Consensus Call: FNV vs SHA1) Nicolas Williams
- Re: [TLS] Collisions (Re: Consensus Call: FNV vs … Nicolas Williams
- Re: [TLS] Collisions (Re: Nico's suggestions - Re… Stefan Santesson
- Re: [TLS] Collisions (Re: Nico's suggestions - Re… Nicolas Williams
- Re: [TLS] Collisions (Re: Consensus Call: FNV vs … Simon Josefsson
- Re: [TLS] Collisions (Re: Nico's suggestions - Re… Stefan Santesson
- Re: [TLS] Collisions (Re: Nico's suggestions - Re… Nicolas Williams
- Re: [TLS] Collisions (Re: Consensus Call: FNV vs … Stefan Santesson
- Re: [TLS] Collisions (Re: Nico's suggestions - Re… Stefan Santesson
- Re: [TLS] Consensus Call: FNV vs SHA1 Hovav Shacham
- Re: [TLS] Collisions (Re: Consensus Call: FNV vs … Simon Josefsson
- Re: [TLS] Consensus Call: FNV vs SHA1 Yoav Nir
- Re: [TLS] Collisions (Re: Nico's suggestions - Re… Martin Rex
- Re: [TLS] Collisions (Re: Nico's suggestions - Re… Nicolas Williams
- Re: [TLS] Collisions (Re: Nico's suggestions - Re… Stefan Santesson
- Re: [TLS] Collisions (Re: Nico's suggestions - Re… Nicolas Williams
- Re: [TLS] Consensus Call: FNV vs SHA1 Nicolas Williams
- Re: [TLS] Collisions (Re: Nico's suggestions - Re… Stefan Santesson
- Re: [TLS] Consensus Call: FNV vs SHA1 Simon Josefsson
- Re: [TLS] Collisions (Re: Nico's suggestions - Re… Nicolas Williams
- Re: [TLS] Consensus Call: FNV vs SHA1 Michael D'Errico
- Re: [TLS] Collisions (Re: Nico's suggestions - Re… Martin Rex
- Re: [TLS] Consensus Call: FNV vs SHA1 Kemp, David P.
- Re: [TLS] Collisions (Re: Nico's suggestions - Re… Nicolas Williams
- Re: [TLS] Consensus Call: FNV vs SHA1 Nicolas Williams
- Re: [TLS] Consensus Call: FNV vs SHA1 Blumenthal, Uri - 0668 - MITLL
- Re: [TLS] Consensus Call: FNV vs SHA1 Nicolas Williams
- Re: [TLS] Collisions (Re: Nico's suggestions - Re… Martin Rex
- Re: [TLS] Collisions (Re: Consensus Call: FNV vs … Kemp, David P.
- Re: [TLS] Collisions (Re: Nico's suggestions - Re… Kemp, David P.
- Re: [TLS] Collisions (Re: Consensus Call: FNV vs … Marsh Ray
- Re: [TLS] Collisions (Re: Nico's suggestions - Re… Nicolas Williams
- Re: [TLS] Collisions (Re: Consensus Call: FNV vs … Nicolas Williams
- Re: [TLS] Collisions (Re: Nico's suggestions - Re… Marsh Ray
- Re: [TLS] Collisions (Re: Nico's suggestions - Re… Marsh Ray
- Re: [TLS] Collisions (Re: Nico's suggestions - Re… Nicolas Williams
- Re: [TLS] Collisions (Re: Consensus Call: FNV vs … Marsh Ray
- Re: [TLS] Collisions (Re: Consensus Call: FNV vs … Nicolas Williams
- Re: [TLS] Collisions (Re: Nico's suggestions - Re… Marsh Ray
- Re: [TLS] [POSSIBLE SPAM] Re: Collisions (Re: Nic… Kemp, David P.
- Re: [TLS] Collisions (Re: Nico's suggestions - Re… Nicolas Williams
- Re: [TLS] [POSSIBLE SPAM] Re: Collisions (Re: Nic… Marsh Ray
- Re: [TLS] [POSSIBLE SPAM] Re: Collisions (Re: Con… Kemp, David P.
- Re: [TLS] Collisions (Re: Nico's suggestions - Re… Marsh Ray
- Re: [TLS] Collisions (Re: Consensus Call: FNV vs … Stefan Santesson
- Re: [TLS] [POSSIBLE SPAM] Re: Collisions (Re: Con… Marsh Ray
- Re: [TLS] Collisions (Re: Nico's suggestions - Re… Stefan Santesson
- Re: [TLS] Collisions (Re: Consensus Call: FNV vs … Marsh Ray
- Re: [TLS] Collisions (Re: Consensus Call: FNV vs … Stefan Santesson
- Re: [TLS] Collisions (Re: Consensus Call: FNV vs … Marsh Ray
- Re: [TLS] Collisions (Re: Nico's suggestions - Re… Simon Josefsson
- Re: [TLS] Collisions (Re: Nico's suggestions - Re… Brian Smith
- Re: [TLS] Collisions (Re: Nico's suggestions - Re… Marsh Ray
- [TLS] Justification Michael D'Errico
- Re: [TLS] Justification Simon Josefsson
- Re: [TLS] Justification Adam Langley
- Re: [TLS] Justification Brian Smith
- Re: [TLS] Justification Michael D'Errico
- Re: [TLS] Justification Adam Langley
- Re: [TLS] Justification Marsh Ray
- Re: [TLS] Justification Brian Smith
- Re: [TLS] [POSSIBLE SPAM] Re: Collisions (Re: Con… Kemp, David P.
- Re: [TLS] Justification Michael D'Errico
- Re: [TLS] Justification Adam Langley
- [TLS] Use HTTP (Re: Justification) Nicolas Williams
- Re: [TLS] Justification Nicolas Williams
- Re: [TLS] Justification Michael D'Errico
- Re: [TLS] Justification Nicolas Williams
- Re: [TLS] Justification Michael D'Errico
- Re: [TLS] Justification Nicolas Williams
- Re: [TLS] Justification Michael D'Errico
- Re: [TLS] Justification Nicolas Williams
- Re: [TLS] Justification Yoav Nir
- Re: [TLS] Justification Michael D'Errico
- Re: [TLS] Justification Martin Rex
- Re: [TLS] Justification Marsh Ray
- Re: [TLS] Justification Stefan Santesson
- Re: [TLS] Justification Martin Rex
- Re: [TLS] Collisions (Re: Nico's suggestions - Re… Yoav Nir
- Re: [TLS] Collisions (Re: Nico's suggestions - Re… Stefan Santesson
- Re: [TLS] Justification Nicolas Williams
- Re: [TLS] Wrapping up cached info Marsh Ray
- Re: [TLS] Collisions (Re: Nico's suggestions - Re… Marsh Ray
- Re: [TLS] Justification Dean Anderson
- [TLS] Wrapping up cached info Stefan Santesson
- Re: [TLS] Wrapping up cached info Nicolas Williams
- Re: [TLS] Wrapping up cached info Simon Josefsson
- Re: [TLS] Wrapping up cached info Nicolas Williams
- Re: [TLS] Justification Stefan Santesson
- Re: [TLS] Justification Nicolas Williams
- Re: [TLS] Justification Nicolas Williams
- Re: [TLS] Wrapping up cached info Marsh Ray
- Re: [TLS] Wrapping up cached info Joseph Salowey (jsalowey)
- Re: [TLS] Wrapping up cached info Marsh Ray
- Re: [TLS] Wrapping up cached info Nicolas Williams
- Re: [TLS] Wrapping up cached info Ben Laurie
- Re: [TLS] Wrapping up cached info Yoav Nir
- Re: [TLS] Wrapping up cached info Nicolas Williams
- Re: [TLS] Wrapping up cached info Marsh Ray
- Re: [TLS] Wrapping up cached info Marsh Ray
- Re: [TLS] Wrapping up cached info Ben Laurie
- Re: [TLS] Wrapping up cached info Martin Rex
- [TLS] Possible alternative to current cached info… Michael D'Errico
- Re: [TLS] Wrapping up cached info (and PRF WTF) Kemp, David P.
- Re: [TLS] Wrapping up cached info (and PRF WTF) Martin Rex
- Re: [TLS] Wrapping up cached info Stefan Santesson
- Re: [TLS] Wrapping up cached info (and PRF WTF) Nicolas Williams
- Re: [TLS] Wrapping up cached info Stefan Santesson
- Re: [TLS] Wrapping up cached info Stefan Santesson
- Re: [TLS] Wrapping up cached info Joseph Salowey (jsalowey)
- Re: [TLS] Wrapping up cached info Stefan Santesson
- Re: [TLS] Wrapping up cached info Michael D'Errico
- Re: [TLS] Wrapping up cached info Marsh Ray
- Re: [TLS] Wrapping up cached info Joseph Salowey (jsalowey)
- Re: [TLS] Wrapping up cached info Joseph Salowey (jsalowey)
- Re: [TLS] Wrapping up cached info Marsh Ray
- Re: [TLS] Wrapping up cached info Nicolas Williams
- Re: [TLS] Wrapping up cached info Stefan Santesson
- Re: [TLS] Wrapping up cached info Michael D'Errico
- Re: [TLS] Wrapping up cached info Michael D'Errico
- Re: [TLS] Wrapping up cached info Kemp, David P.
- Re: [TLS] Wrapping up cached info Nicolas Williams
- Re: [TLS] Wrapping up cached info Nicolas Williams
- Re: [TLS] Wrapping up cached info Ben Laurie
- Re: [TLS] Wrapping up cached info Brian Smith
- Re: [TLS] Wrapping up cached info Stefan Santesson
- Re: [TLS] Wrapping up cached info Martin Rex
- Re: [TLS] Wrapping up cached info Brian Smith
- Re: [TLS] Wrapping up cached info Nicolas Williams
- Re: [TLS] Wrapping up cached info Stefan Santesson
- Re: [TLS] Wrapping up cached info Brian Smith
- Re: [TLS] Wrapping up cached info Brian Smith
- Re: [TLS] Wrapping up cached info Nicolas Williams