Re: [Cfrg] Formal request from TLS WG to CFRG for new elliptic curves
Simon Josefsson <simon@josefsson.org> Wed, 16 July 2014 21:39 UTC
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From: Simon Josefsson <simon@josefsson.org>
To: "Paterson, Kenny" <Kenny.Paterson@rhul.ac.uk>
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Date: Wed, 16 Jul 2014 23:39:41 +0200
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Subject: Re: [Cfrg] Formal request from TLS WG to CFRG for new elliptic curves
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I'm reviewing the selection criteria. Some of the requirements are rather fine-grained and poorly justified, and appear to limit the search space. If taken literally, I believe they exclude some good candidates and steer the selection into a rather small field of available options. I'm fine with R1-R3. "Paterson, Kenny" <Kenny.Paterson@rhul.ac.uk> writes: > Intellectual Property > > R4. Required: available worldwide under reasonable and well > understood licensing terms [1] > > R5. Desired: available worldwide under royalty-free licensing > terms [1] I believe non-royalty-free licensing terms is a nonstarter. I suggest collapsing this into: R4'. Required: available for worldwide implementation (by both proprietary and free open source software) and use under well understood and royalty-free licensing terms > Interoperability > > R6. Desired: can be used with current software implementations > (using different curve parameters) of TLS, PKIX, SSH, and IKE [4] > > R7. Desired: can be used within current ECC standards of TLS, > PKIX, SSH, and IKE [4] I do not see why these are desirable properties, so I disagree they should be a selection criteria. These properties restricts the search space. I would prefer if the CFRG are at liberty to recommend the best alternative even if it is clearly not re-usable in existing software or standards. I would go even further saying that one of the reasons for doing this excercise is that the existing software and standards are not sufficient. On the topic of interoperability, I would propose to add the following, to me, more important property: Rx. Desired: either a clear algorithm description exists (with clarity on byte-ordering etc) or multiple interoperable implementations are available. If some alternative does not appear to be sufficiently specified or widely implemented, the CFRG could take on driving a document to clarify the solution. > Security > > R8. Required: amenable to constant-time implementations, to avoid > side channel attacks [2] > > R9. Required: resist twist attacks [2] > > R10. Required: curve parameters should have good provenance; > random curves should be provably pseudorandom [5] > > R11. Desired for key exchange: resist invalid curve attacks [2]; > note that complete addition laws help and are thus desirable [2]. > (Note that the use of ephemeral keys also resist such attacks.) Instead of R8-R11, I suggest to summarize this more generally as: R8'. Required: the solution should be secure against reasonable and well-understood threats, including (but not limited to and necessarily not all of) brute-force, side-channel, invalid-curve, twist attacks, or maliciously chosen curve parameters. Designing against security threats is a balance, and I would say that there are no perfect solutions. Every solution will have some area where they perform less well compared to some other solution. I believe the overall choice(s) should reflect well-balanced alternatives with strong advantages and some understood disadvantages. > R12. Required for PAKE: indistinguishability of curve points from > random strings [2] I do not see why this is a desirable property for TLS, or other IETF areas, so I disagree it should be a requirement. /Simon
- [Cfrg] Formal request from TLS WG to CFRG for new… Paterson, Kenny
- Re: [Cfrg] Formal request from TLS WG to CFRG for… Watson Ladd
- Re: [Cfrg] Formal request from TLS WG to CFRG for… Michael Hamburg
- Re: [Cfrg] Formal request from TLS WG to CFRG for… Ben Laurie
- Re: [Cfrg] Formal request from TLS WG to CFRG for… Johannes Merkle
- Re: [Cfrg] Formal request from TLS WG to CFRG for… Watson Ladd
- Re: [Cfrg] Formal request from TLS WG to CFRG for… Michael Hamburg
- Re: [Cfrg] Formal request from TLS WG to CFRG for… Joseph Salowey (jsalowey)
- Re: [Cfrg] Formal request from TLS WG to CFRG for… Andy Lutomirski
- Re: [Cfrg] Formal request from TLS WG to CFRG for… Simon Josefsson
- Re: [Cfrg] Formal request from TLS WG to CFRG for… Dan Harkins
- Re: [Cfrg] Formal request from TLS WG to CFRG for… Benjamin Black
- Re: [Cfrg] Formal request from TLS WG to CFRG for… Benjamin Black
- Re: [Cfrg] Formal request from TLS WG to CFRG for… Benjamin Black
- Re: [Cfrg] Formal request from TLS WG to CFRG for… Igoe, Kevin M.
- Re: [Cfrg] Formal request from TLS WG to CFRG for… Paterson, Kenny
- Re: [Cfrg] Formal request from TLS WG to CFRG for… Joseph Salowey (jsalowey)
- Re: [Cfrg] Formal request from TLS WG to CFRG for… Benjamin Black
- Re: [Cfrg] Formal request from TLS WG to CFRG for… Benjamin Black
- Re: [Cfrg] Formal request from TLS WG to CFRG for… Watson Ladd
- Re: [Cfrg] Formal request from TLS WG to CFRG for… Paterson, Kenny
- Re: [Cfrg] Formal request from TLS WG to CFRG for… Manuel Pégourié-Gonnard
- Re: [Cfrg] Formal request from TLS WG to CFRG for… Nigel Smart
- Re: [Cfrg] Formal request from TLS WG to CFRG for… Salz, Rich
- Re: [Cfrg] Formal request from TLS WG to CFRG for… Tanja Lange
- Re: [Cfrg] Formal request from TLS WG to CFRG for… Michael Hamburg
- Re: [Cfrg] Formal request from TLS WG to CFRG for… Nigel Smart
- Re: [Cfrg] Formal request from TLS WG to CFRG for… Watson Ladd
- Re: [Cfrg] Formal request from TLS WG to CFRG for… Michael Hamburg
- Re: [Cfrg] Formal request from TLS WG to CFRG for… Patrick Longa Pierola
- Re: [Cfrg] Formal request from TLS WG to CFRG for… Brian LaMacchia
- Re: [Cfrg] Formal request from TLS WG to CFRG for… Andrey Jivsov
- Re: [Cfrg] Formal request from TLS WG to CFRG for… Watson Ladd
- Re: [Cfrg] Formal request from TLS WG to CFRG for… Andrey Jivsov
- Re: [Cfrg] Formal request from TLS WG to CFRG for… David McGrew
- Re: [Cfrg] Formal request from TLS WG to CFRG for… Watson Ladd
- Re: [Cfrg] [TLS] Formal request from TLS WG to CF… Salz, Rich
- Re: [Cfrg] Formal request from TLS WG to CFRG for… Joachim Strömbergson
- Re: [Cfrg] [TLS] Formal request from TLS WG to CF… Benjamin Black
- Re: [Cfrg] [TLS] Formal request from TLS WG to CF… Peter Gutmann