ETSI TS 135 206 defines the specification of MILENAGE algorithm which is an authentication algorithm for mobile networks.
It defines 'OPc' as below:
a 128-bit value derived from OP and K and used within the computation of the functions.
According to mentioned standard it is calculated as below:
OPc = OP ⊕ E(OP,K)
which E(x,k) = the result of applying the Rijndael encryption algorithm to the 128-bit value x under the 128-bit key k.
My question is about the method to calculate OPc without direct access to OP value. Since OP value is stored in devices such as HSM and mobile operators do not allow their vendors to access this key directly and allow them to encrypt values using it by HSM APIs.
So I want to know are there any methods which I can calcualte the OPc value in case I have OP inside and HSM and know the K value?
