[Sip-security] Re: [Sipping] SIP authentication problem when using RES in Digest-AKA

Hi All,

On 03/15/2002 08:16 AM, ext Jari Arkko wrote:
> John, Greg,
> 
> Thanks for an interesting describing this interesting attack! I believe
> while making draft-niemi the authors have been assuming that we do not
> use the GSM compatibility mode (which I believe is the reason why the RES
> could be only 32 bits). That is, when full AKA is used this isn't a problem.
> 
> So, we could either
> 
> (1) Require the full use of AKA
> (2) Switch to using IK and not RES as input in the Digest process

As far as I understand the authentication/integrity protection schemes 
of 3GPP IMS, the authentication is between the UE and the S-CSCF, and 
the integrity protection is between the UE and the P-CSCF. Therefore I 
can't see a problem in using RES as input for Digest AKA in the 
authentication, and IK as input for the Digest in integrity protection.

The RES would then constitute a one-time password type key, whereas IK 
is a more long term key for integrity protection.

I don't see a need to group the two mechanisms together.

Cheers,
Aki

> Greg, is the IK free of similar limitations when GSM compatibility
> is used?
> 
> Jari
> 
> 
> 
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