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determining the initialization vector in CBC mode


RFC2409 states:

     In phase 1, material for the initialization vector (IV material)
     CBC mode encryption algorithms is derived from a hash of a
     concatenation of the initiator's public Diffie-Hellman value and
     responder's public Diffie-Hellman value using the negotiated hash
     algorithm. This is used for the first message only.

Do I assume SKEYID_e is the key for the hash alforithmi.e.

    IV  = prf(SKEYID_e, g^xi | g^xr)

Any input would be appreciated.


Peadar Harmon