Re: [secdir] Secdir review of draft-ietf-ipsecme-implicit-iv-07

Hi Magnus,

Thanks for this review -- I filed a Discuss point about the inconsistency
between the text and the codepoints for whether AES-CTR is covered.

-Ben

On Sun, Oct 13, 2019 at 10:46:30PM -0700, Magnus Nyström wrote:
>  I have reviewed this document as part of the security directorate's
> ongoing effort to review all IETF documents being processed by the IESG.
> These comments were written primarily for the benefit of the security area
> directors.  Document editors and WG chairs should treat these comments just
> like any other last call comments.
> 
> This document defines a mechanism to save on bandwidth in ESP connections
> when certain ciphers have been negotiated by using implicit IVs. The
> savings are limited to 8 bytes for the current version of this document.
> 
> 
> 
>    - Section 2 mentions AES-CCM, AES-CTR, AES-GCM and ChaCha. For all of
>    these ciphers, an 8-byte nonce is used. The mechanism to make the IV
>    implicit is by coupling it to the sequence number. Yet, Section 4 gives two
>    examples of sequence numbers, one  of 4 bytes and one of 8 bytes. This is
>    confusing, presumably only the extended sequence number is usable?
>    - Also, while the Abstract says the memo offers a mechanism to save on
>    the explicit IV also for AES-CTR, and Section 2 includes AES-CTR in its
>    description, Section 4 explicitly states that only AES-CCM, AES-GCM and
>    ChaCha are subject of the optimization in this memo. This is also
>    confusing. Why including AES-CTR in the memo at all if it isn't covered? At
>    the very least it seems the Abstract should be updated.
>    - It would be very helpful and useful to include an example of a
>    handshake with an IIV and the resulting IV in an Appendix; this could
>    assist implementors to get things right.
> 
> 
> (Editorial: English grammar needs some updates/reviews)
> 
> Thanks,
> -- Magnus

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