[IPsec] Comments on draft-ietf-ipsecme-implicit-iv

["Scott Fluhrer (sfluhrer)" <[e-mail]>]

-          Section 4: "Section 3.5 of [RFC6407] explains how repetition MAY BE prevented by using a prefix for each group member"
Actually, RFC6407 just refers to RFC6054; that has the SID in the top 8 bits of the 8 byte sequence number.  Used literally, this doesn't work, as the top 8 bits of the 8 byte sequence number are never expressed in the packet in implicit-iv.  You could put them in the top 8 bits of the 4 byte sequence number (which means you can't use ESN, but it didn't work in the multisender case anyways), but that would mean that each sender would be limited to 16M packets. I believe that these details are distinct enough that (if this is considered a viable alternative) they should be explicitly listed (including the 16M packet restriction).  Alternatively, we can just forbid this transform in the multisender case.


-          Section 6: "The rules of SA payload processing ensure that the responder will never send an SA payload containing the IIV indicator to an initiator that does not support IIV"

I believe that this is stale text; the current draft doesn't use an indicator; instead, it defines separate transforms IDs.


-          Section 8 has "AES-CTR ... [is] likely to implement the implicit IV described in this document"; however the transform ENCR_AES_CTR_IIV is not defined.  Is this intended?  Should we either remove the AES-CTR algorithm from the list of "likely to implement", or should we actually define the transform id for it?