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RE: src addr/SPI coupling
At 3:33 AM -0400 5/13/01, Andrew Krywaniuk wrote:
> > In the case of multicast traffic, where separate key servers may be
>> controlling keys/SA assignment for different multicast sessions,
>> you'd have to come up with a mechanism to ensure that there are
>> (a) no collisions in SPI assignment across the possible universe of
>> key servers, (b) but still have reasonable randomness to the SPI
>> allocation (the phase 2 SPIs are used as additional randomness
>> in the key derivation), and (c) the SPI space per address is
>> sufficiently
>> large enough for rekeying for some noticeable amount of time (because
>> of (b)).
>
>Are (b) and (c) really a problem? The entropy provided by the SPIs is only
>needed to provide distinct keymat for multiple SAs in the same packet,
>right? A counter in the key derivation would serve the same purpose.
>
There is no security requirement, re key material derivation, for
SPIs to be "random." There is some benefit for DoS purposes to have
them be hard to predict, but RFC 2401 does not mandate randomness. It
merely requires local uniqueness, for demuxing.
steve
References: