Subject: [secdir] Secdir review of draft-ietf-isis-hmac-sha-07

From: "Carl Wallace" <[email-masked]>
Date: Mon, 8 Dec 2008 08:05:55 -0500

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 draft defines a new authentication type for IS IS and describes how
to use HMAC-SHAx with this authentication type.  The draft is well
written and the security considerations section looks good to me.  A few
minor comments:

The definition of Authentication Key in section 2 states that the length
of the key "depends upon the authentication algorithm".  Section 3.3
describes how to prepare keys of various lengths, allowing the length of
the key to vary independent of the algorithm.  
 
Given RFC5304, is MD5 allowed or disallowed with this authentication
type?  Seems like the doc should state one way or another.

Section 3.3 items (2) and (3) might benefit from clarifying that Ko is
padded with zeroes to be B bytes in length and that || means
concatenate.  

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From: "Bhatia, Manav (Manav)" <[email-masked]>
Date: Mon, 8 Dec 2008 21:31:36 +0530

Hi Carl,

Thanks for the review.

> the key to vary independent of the algorithm.  

Following the terminology used in Sec 3.3, the key referred to in Sec 2
is Ko, while the key being mentioned in section 3.3 is K. 

Since Ko is the cryptographic key used with the hash function, it is
*this* key that is associated with the Security Association. However,
this is internal to the implementation and the user is unaware of this.
The user enters the Key K, and Section 3.3 describes how the user
entered key needs to be converted into the cryptographic key being used
the crypto mathematics.

> type?  Seems like the doc should state one way or another.

This mechanism described in this draft is used in addition to 5304. We
do mention this in the Abstract. We can make it more explicit.

> padded with zeroes to be B bytes in length and that || means

Ko is L octets long, where L is the length of the hash function being
used. We do mention that if K is less than L, then Ko is set to K with
zeroes appended to the end of K such that Ko is L octets long. Refer to
(1) of Sec 3.

Cheers, Manav