Re: [Ipsec] Question about Integrity Checksum Data

So if I'm using the UI suite VPN-A, whenever I'm using IKEv1 I will use 
the integrity algorithm SHA1 (with a 160-bit checksum field), but 
whenever I'm using IKEv2 I will use the SHA1_96 integrity algorithm 
(with a 96-bit checksum field).

Is this correct?

On May 30, 2005, at 1:43 AM, Paul Hoffman wrote:

> At 7:25 AM +0300 5/29/05, Yoav Nir wrote:
>> It is strange.  If you read RFC 4109 (algorithms for IKEv1) or the 
>> IANA registry, it says just MD5 or SHA1, and in fact implementations 
>> of IKEv1 did use the full checksum (128 or 160 bits).
>
> Nothing strange so far.
>
>> However, the UI-suites document and the algorithms document show only 
>> the _96 version of these algorithms. Is this difference intentional? 
>> Does this mean that for an IKEv1 implementation to support the VPN-A 
>> suite it would need to have a new algorithms for integrity?
>
> Because we changed from not negotiating the actual PRF in IKEv1 to 
> negotiating it in IKEv2, the UI-suites document had to pick between 
> one of the two wordings; I chose the IKEv2 wording.
>
> In IKEv1, it says:
>
>    All of these attributes are mandatory and MUST be negotiated. In
>    addition, it is possible to optionally negotiate a psuedo-random
>    function ("prf").  (There are currently no negotiable pseudo-random
>    functions defined in this document. Private use attribute values can
>    be used for prf negotiation between consenting parties). If a "prf"
>    is not negotiation, the HMAC (see [KBC96]) version of the negotiated
>    hash algorithm is used as a pseudo-random function. Other non-
>    mandatory attributes are described in Appendix A. The selected hash
>    algorithm MUST support both native and HMAC modes.
>
> Thus, when you negotiate a hash algorithm of "SHA1", you are really 
> negotiating the PRF of "HMAC-SHA1" and the use of SHA1 in other places 
> in the protocol. Maybe instead of:
>    Pseudo-random function   HMAC-SHA1 [RFC2104]
> I could have said:
>    Hash (IKEv1) or pseudo-random function (IKEv2)   SHA1 [SHA1] or 
> HMAC-SHA1 [RFC2104]
> but that would be harder to understand.
>
> --Paul Hoffman, Director
> --VPN Consortium

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