Hi All,

Forgive me if this has been discussed and I missed it.  But, to
improve quantum resistance should the draft recommend AES-256 over
AES-128?  I realize that the RFC 4493 construction specifically uses
AES-128, but is there any barrier to using AES-256?

Similarly, the draft says that the "MAC tag SHOULD be 128 bits long"
but doesn't describe any situations where the MAC tag would be another
length.  Given that a tags that are not an integer multiple of 32-bit
words violate RFC 5905 and it appears that MAC tags that are not
128-bits in length also violate RFC 5905.  (In practice ntp.org's ntpd
handles MAC tags up to 160-bits in length gracefully, but RFC 5905 appears
to restrict MAC tag length to 128-bits.)

If there are situations where the MAC tags MAY be a length other than
128-bits, it would probably be useful to articulate the criteria for
acceptable MAC tag lengths.

Cheers,
Matt



On Wed, Aug 09, 2017 at 04:53:43AM +0000, Karen O'Donoghue wrote:
> Folks,
> 
> This begins a three week working group last call (WGLC) for "Message 
> Authentication Code for the Network Time Protocol"
> https://datatracker.ietf.org/doc/draft-ietf-ntp-mac/
> 
> Please review and provide comments to the mailing list by no later than 31 
> August 2017. Earlier comments and discussion would be appreciated. Please 
> note that the chairs will be using this WGLC to determine consensus to move 
> this document forward to the IESG.
> 
> Also, as a reminder, we have migrated the working group mailing list to IETF 
> infrastructure. Please respond to [email protected]<mailto:[email protected]>.
> 
> Regards,
> Karen and Dieter

> _______________________________________________
> ntp mailing list
> [email protected]
> https://www.ietf.org/mailman/listinfo/ntp


-- 
Matthew Van Gundy, Technical Leader
Advanced Security Initiatives Group
Cisco Systems, Inc.

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