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Re: [Dcrup] I-D draft-ietf-dcrup-dkim-crypto-06

Jeremy Harris <jgh@wizmail.org> Wed, 13 September 2017 18:47 UTC

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Subject: Re: [Dcrup] I-D draft-ietf-dcrup-dkim-crypto-06
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On 13/09/17 18:41, John R Levine wrote:
> I have sent in a new draft which is intended to take into account all of
> the comments I've seen.

Section 4 says to use the Pure variant of Ed25519, which section 4
of rfc 8032 appears to describe as (my paraphrase) sign only; not
hashing the data handed to it.  What we hand to it is already a
hash, using sha256.

Do I have that right?

The existing interfaces in both GnuTLS and OpenSSL appear to
be aiming towards a Hash version of Ed25519, if I read them right -
and they don't say explicitly what the hash-function is.

For example, https://gnutls.org/reference/gnutls-abstract.html
says, for gnutls_privkey_sign_hash() :-

"Note that, not all algorithm support signing already hashed data. When
 signing with Ed25519, gnutls_privkey_sign_data() should be used."

(I'm assuming that ...sign_data() does a hash and then signs.  I also
fear, reading between some lines, that the hash might not be sha256).


Are we expecting these libraries to enhance their APIs?
Or am I totally off track?
-- 
Thanks,
  Jeremy

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