Re: [Dcrup] draft-ietf-dcrup-dkim-crypto-00

[Jim Fenton <[e-mail]>]

On 5/19/17 11:48 AM, John R Levine wrote:
>> Speaking as an individual, I'd like to emphasize what Mark said. 
>> ECDH is a key exchange protocol, not a signing protocol.  For
>> elliptic curve signatures, the document should use
>> https://datatracker.ietf.org/doc/draft-ietf-curdle-cms-eddsa-signatures/
>> which is now in IESG last call.  Note that the hash mechanism is
>> implicit in the signature algorithm.
>
> That's fine, like I said I don't purport to be a crypto expert.  Even
> better, send text.
>
>> The key fingerprint needs more clarification.  For 25519 keys, there
>> is a "natural and obvious" byte representation, but for RSA keys what
>> is being fingerprinted?  The DER OCTET STRING?
>
> IIM had key fingerprints.  Perhaps Jim can tell us what it did.

>From https://www.ietf.org/archive/id/draft-fenton-identified-mail-02.txt :

The fingerprint is created as follows: create the binary
representation of the RSA exponent (e) and modulus (n) and
concatenate them as e|n.  Run this value through SHA1 over the
full length and convert the first 12 bytes of the output of the
SHA1 operation to base 64.  That is, base64 (TRUNC (SHA1 ((e|n)),12)

-Jim