Wimax standards and Security The Wimax

FIGURE 12.9
The mutual authorization process between an SS and the BS.

3. 
   The BS provides the authenticated SS with the AK, and then a KEK and message authentication keys are derived from this AK.
   
4. 
   The BS provides the authenticated SS with the identities (i.e., the SAIDs) and properties of SAs from which the SS can obtain the encryption key information for subsequent transport connections.
   

Figure 12.9 shows the mutual authorization process between an SS and the BS. Similar to PKMv1, the SS sends an authorization request message to the target BS, requesting an AK immediately after sending the authentication information message. The authentication information message is the same as that in PKMv1. As compared to the authorization request message in PKMv1, an SS running PKMv2 adds a 64-bit random number N_S in the authorization request message. This N_S is returned in the authorization reply message from the BS to the SS in securing the authentication process. PKMv2 also adds a 64-bit random number N_B, the BS’s X.509 certificate, and BS’s signature in the authorization reply message. The random numbers N_S and N_B are included in the exchange, and both the SS and BS can check the replied numbers to ensure the time freshness of the message, and thus to prevent the replay attack. Table 12.1 summarizes the contents in the authorization request and autho- rization reply messages.

TABLE 12.1
Authorization Request and Authorization Reply messages
Authorization Request Message Authorization Reply Message

The manufacturer-issued X.509 The BS’s X.509 certificate, used to verify the BS’s certificate identity

The security capabilities the requesting A pre-PAK encrypted with the SS’s public key SS supports A 4-bit PAK sequence number
The SS’s basic CID, which is the The lifetime of the pre-PAK first static CID the BS assigns to an The identities (i.e., the SAIDs)
SS during initial ranging The 64-bit random number generated by the SS A 64-bit random number N_S generated A 64-bit random number N_B generated by the BS
by the SS The BS’s signature




AK = Dot16KDF (PAK, SS MAC Address | BSID | PAK | “PAK’’, 160)



FIGURE 12.10
AK derivation in RSA-based authorization.

2.