A8 (algorithm)

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The key production algorithm A8 computes the key Kc (64 bits) in GSM nets from the secret participant key AI (128 bits) and a random number EDGE (128 bits). The Kc is used for the coding algorithm A5 for the coding of the air interface. The A8 is both in the Authentication center (AuC) and implemented on SIM of the participant. Kc (session key) is stored in the SIM and in the HLR. A suitable algorithm can be selected by the network carrier freely and is not standardized therefore not in GSM. The interface for the algorithm however is standardized. Nevertheless there is example implementations of the portable radio network carrier combination GSMA. Since the authentication algorithm A3 and the A8 have the same initial parameters, these are called frequently together implemented A3/A8, also admits as COMP128.