Re: [sidr] Stephen Farrell's Discuss on draft-ietf-sidr-bgpsec-protocol-21: (with DISCUSS and COMMENT)

while i would also like to see less use of sha-1 in new network protocols...
limiting the SKI length to a fixed 20 bytes is not really a bad idea for implementation efficiency and interoperability.
as Sean points out, rfc7093's straight forward (leftmost 160 bits --20bytes) of a SHA-2 algorithm digest works well for the use of a hash value in this particular context (generating Key Identifiers)..
mA      From: Sean Turner <sean@sn3rd.com>
 To: Stephen Farrell <stephen.farrell@cs.tcd.ie> 
Cc: sidr-chairs@ietf.org; draft-ietf-sidr-bgpsec-protocol@ietf.org; The IESG <iesg@ietf.org>; m.waehlisch@fu-berlin.de; sidr@ietf.org
 Sent: Wednesday, January 4, 2017 10:48 AM
 Subject: Re: [sidr] Stephen Farrell's Discuss on draft-ietf-sidr-bgpsec-protocol-21: (with DISCUSS and COMMENT)

> On Jan 4, 2017, at 08:53, Stephen Farrell <stephen.farrell@cs.tcd.ie> wrote:
> 
> Stephen Farrell has entered the following ballot position for
> draft-ietf-sidr-bgpsec-protocol-21: Discuss
> 
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> Please refer to https://www.ietf.org/iesg/statement/discuss-criteria.html
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> The document, along with other ballot positions, can be found here:
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> 
> 
> ----------------------------------------------------------------------
> DISCUSS:
> ----------------------------------------------------------------------
> 
> 
> 
> I have a couple of fairly straightforward things I'd
> like to briefly discuss...
> 
> (1) 3.2/Figure 7: A fixed 20 byte SKI being a sha-1 hash
> of the public key is a bad plan, for all the usual
> reasons. Why is it ok for that to be hardcoded here when
> it could change if/when new alg choices are made for the
> RPKI? If it is not too late then I think you should add a
> length or alg field to that. If it is too late to do that,
> then are we really ok that you will need to rev the BGPsec
> version number in order to get rid of all sha-1 code from
> your implementation? That seems like a bad plan for a new
> protocol.

Not sure it absolutely needs a length field; if the RPKI does ever decide to change to another hash algorithm for SKI, e.g., SHA-256/384/512, or to change to a hash of the SubjectPublicKeyInfo they could always the procedures from https://datatracker.ietf.org/doc/rfc7093/ to generate the values for a 20-byte value.  

spt
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