[tcpm] Re: Feedback on draft-ietf-tcpm-tcp-ao-algs-00

[Eric Biggers <[e-mail]>]

On Tue, Apr 28, 2026 at 03:23:59PM +0000, Bonica, Ron wrote:
> Eric,
> 
> Thanks for the review. I suspect that we will trim the list of proposed algorithms. Version-00 of the draft was just a starting point.
> 
> You say:
> 
> "I suggest simplifying the proposal to just HMAC-SHA256 for now.  That's the only one that seems like an obvious choice.  Indeed, SHA-256 is the usual replacement for the outdated SHA-1."
> 
> Do you mean HMAC-SHA256-128? Or do you really mean HMAC-SHA256?
> 
> I propose HMAC-SHA256 in draft-bonica-tcpm-tcp-ao-long-algs<https://datatracker.ietf.org/doc/draft-bonica-tcpm-tcp-ao-long-algs/>. But if we go there, we need to solve the problem identified in TCP Extended Options<https://datatracker.ietf.org/doc/draft-bonica-tcpm-extended-options/>.

By "HMAC-SHA256-128" you just mean HMAC-SHA256 with the output truncated
to 128 bits, right?  I wasn't implying that you wouldn't need to do that
truncation.  The TCP options header doesn't have enough space for the
full output, after all.

Note that the full HMAC-SHA256 output still must be used in the KDF.

- Eric