Re: [tcpinc] Eric Rescorla's Discuss on draft-ietf-tcpinc-tcpcrypt-09: (with DISCUSS and COMMENT)
Eric Rescorla <ekr@rtfm.com> Wed, 21 November 2018 21:59 UTC
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From: Eric Rescorla <ekr@rtfm.com>
Date: Wed, 21 Nov 2018 13:59:04 -0800
Message-ID: <CABcZeBP_x91zXJv-F07ptxSduwWq-7va=_hpwW8J1sgDKMh5pA@mail.gmail.com>
To: Daniel B Giffin <dbg@scs.stanford.edu>
Cc: mazieres-nj788xtv7k4q4yq2nedg4eupms@temporary-address.scs.stanford.edu, tcpinc <tcpinc@ietf.org>, Kyle Rose <krose@krose.org>, tcpinc-chairs@ietf.org, "Black, David" <David.Black@dell.com>, IESG <iesg@ietf.org>, draft-ietf-tcpinc-tcpcrypt@ietf.org
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Subject: Re: [tcpinc] Eric Rescorla's Discuss on draft-ietf-tcpinc-tcpcrypt-09: (with DISCUSS and COMMENT)
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On Thu, Nov 8, 2018 at 1:19 PM Daniel B Giffin <dbg@scs.stanford.edu> wrote: > Eric Rescorla wrote: > [..] > > I am not an EC expert, but my impression based on the discussion in TLS > was > > that checking for the zero value for X25519 was not sufficient defense > > against malicious peers if you didn't use the 7748 computations, hence > the > > language in 8446. Do you believe otherwise? > > The draft currently says: > > Key-agreement schemes ECDHE-Curve25519 and ECDHE-Curve448 use the > functions X25519 and X448, respectively, to perform the Diffie-Helman > protocol as described in [RFC7748]. Implementations MUST check > whether the computed Diffie-Hellman shared secret is the all-zero > value and abort if so, as described in Section 6 of [RFC7748]. [...] > > This requires, perhaps too gently, the (Montgomery ladder) > algorithm in RFC 7748. > OK, I did not read it that way. It would be fine with me if you made this sharper. I.e., "Implementations MUST use the Montgomery ladder as specified in [RFC7748] and MUST check whether..." > But it is not clear exactly what "additional checks" are > required (reject all invalid keys?), Yeah, I agree that this isn't maximally clear. and for what purpose > (ensure some "contributory behavior" property?) > Yes. It seems the only observable difference would be that other > algorithms might abort on some invalid DH inputs that the > RFC 7748 algorithm accepts. > > So there are two orthogonal questions here: > > - Should tcpcrypt allow implementations that behave > differently from RFC 7748? > > - Given that tcpcrypt does not depend on any "contributory > behavior" property, is there any use in requiring DH input > validation? > See my response to David. Elsewhere we have been opting for belt and suspenders. -Ekr > If other algorithms are allowed *and* input validation is > required, it seems we will have to explain more clearly what > validation entails. > > d > >
- [tcpinc] Eric Rescorla's Discuss on draft-ietf-tc… Eric Rescorla
- Re: [tcpinc] Eric Rescorla's Discuss on draft-iet… Kyle Rose
- Re: [tcpinc] Eric Rescorla's Discuss on draft-iet… Eric Rescorla
- Re: [tcpinc] Eric Rescorla's Discuss on draft-iet… Kyle Rose
- Re: [tcpinc] Eric Rescorla's Discuss on draft-iet… Eric Rescorla
- Re: [tcpinc] Eric Rescorla's Discuss on draft-iet… Kyle Rose
- Re: [tcpinc] Eric Rescorla's Discuss on draft-iet… Daniel B Giffin
- Re: [tcpinc] Eric Rescorla's Discuss on draft-iet… Daniel B Giffin
- Re: [tcpinc] Eric Rescorla's Discuss on draft-iet… Eric Rescorla
- Re: [tcpinc] Eric Rescorla's Discuss on draft-iet… Eric Rescorla
- Re: [tcpinc] Eric Rescorla's Discuss on draft-iet… Black, David
- Re: [tcpinc] Eric Rescorla's Discuss on draft-iet… Daniel B Giffin
- Re: [tcpinc] Eric Rescorla's Discuss on draft-iet… Daniel B Giffin
- Re: [tcpinc] Eric Rescorla's Discuss on draft-iet… Eric Rescorla
- Re: [tcpinc] Eric Rescorla's Discuss on draft-iet… Kyle Rose
- Re: [tcpinc] Eric Rescorla's Discuss on draft-iet… Eric Rescorla
- Re: [tcpinc] Eric Rescorla's Discuss on draft-iet… Black, David
- Re: [tcpinc] Eric Rescorla's Discuss on draft-iet… Eric Rescorla
- Re: [tcpinc] Eric Rescorla's Discuss on draft-iet… Kyle Rose
- Re: [tcpinc] Eric Rescorla's Discuss on draft-iet… Eric Rescorla
- Re: [tcpinc] Eric Rescorla's Discuss on draft-iet… Kyle Rose
- Re: [tcpinc] Eric Rescorla's Discuss on draft-iet… Black, David
- Re: [tcpinc] Eric Rescorla's Discuss on draft-iet… Daniel B Giffin
- Re: [tcpinc] Eric Rescorla's Discuss on draft-iet… Kyle Rose
- Re: [tcpinc] Eric Rescorla's Discuss on draft-iet… Daniel B Giffin
- Re: [tcpinc] Eric Rescorla's Discuss on draft-iet… Kyle Rose
- Re: [tcpinc] Eric Rescorla's Discuss on draft-iet… Eric Rescorla
- Re: [tcpinc] Eric Rescorla's Discuss on draft-iet… David Mazieres
- Re: [tcpinc] Eric Rescorla's Discuss on draft-iet… Eric Rescorla
- Re: [tcpinc] Eric Rescorla's Discuss on draft-iet… David Mazieres
- Re: [tcpinc] Eric Rescorla's Discuss on draft-iet… Eric Rescorla
- Re: [tcpinc] Eric Rescorla's Discuss on draft-iet… David Mazieres
- Re: [tcpinc] Eric Rescorla's Discuss on draft-iet… Daniel B Giffin
- Re: [tcpinc] Eric Rescorla's Discuss on draft-iet… Eric Rescorla
- Re: [tcpinc] Eric Rescorla's Discuss on draft-iet… Eric Rescorla
- Re: [tcpinc] Eric Rescorla's Discuss on draft-iet… Daniel B Giffin
- Re: [tcpinc] Eric Rescorla's Discuss on draft-iet… Eric Rescorla
- Re: [tcpinc] Eric Rescorla's Discuss on draft-iet… Daniel B Giffin