Re: [Cfrg] Point format endian (was: Adoption of draft-ladd-spake2 as a RG document)

Peter Gutmann <pgut001@cs.auckland.ac.nz> Mon, 26 January 2015 10:20 UTC

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From: Peter Gutmann <pgut001@cs.auckland.ac.nz>
To: "'cfrg@irtf.org'" <cfrg@irtf.org>
Thread-Topic: [Cfrg] Point format endian (was: Adoption of draft-ladd-spake2 as a RG document)
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Date: Mon, 26 Jan 2015 10:20:34 +0000
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Subject: Re: [Cfrg] Point format endian (was: Adoption of draft-ladd-spake2 as a RG document)
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Mike Hamburg <mike@shiftleft.org>; writes:

>But will the endian complicate the implementation of the new curves?

Given that every single crypto bignum representation that I'm aware of (X.509,
S/MIME, PGP, SSH, TLS, OCSP, CMP, TSP, and many more) are all big-endian,
there are probably lots of crypto libraries that simply don't have little-
endian import/export routines.  Looking at BN_bn2bin()/BN_bin2bn() from one
widely-used library that powers half the Internet (and mobile phone market),
it only supports the big-endian format.  So that's automatic non-support for
the world's most widely-used crypto library outside of MS CryptoAPI (which
doesn't expose its bignum library).

I can't believe we're even having this endless discussion.  The universal
standard for external representations of bignums in IETF protocols is big-
endian.  Even the PGP and S/MIME, and SSH and TLS, folks have managed to agree
on that one.

Peter.