Re: [babel] [Last-Call] Secdir last call review of draft-ietf-babel-mac-relaxed-04

[Christian Huitema <[e-mail]>]

On 4/9/2023 4:51 AM, Juliusz Chroboczek wrote:
> Thank you for your review.  I must, however, most respectfully disagree
> with your conclusions: the protocol is not vulnerable to the attacks that
> you describe.
> 
>> In order to relax the packet counter checks used to detect duplicate messages,
>> the draft recommends doing separate checks for packets received in unicast and
>> multicast mode. However, the two modes use the same packet counter. Attackers
>> can replay in multicast mode packets send in unicast mode, and bypass the
>> proposed check.
> No, they cannot.  If a packet originally sent to a unicast address is
> resent to a multicast address, this will be reflected in the pseudo-header
> (RFC 8967 Section 4.1).  Since the pseudo-header participates in HMAC
> computation, this will cause the HMAC test to fail (RFC 8967 Section 4.3,
> first bullet point).

You are correct. I have revised my review.

-- Christian Huitema