5 An alternative algorithm (informative)

3GPP55.205Release 17Specification of the GSM-MILENAGE algorithms: An example algorithm set for the GSM Authentication and Key Generation Functions A3 and A8TS

The GSM-MILENAGE algorithms defined in section 3 are obtained by applying standard 3G-to-2G conversion functions defined in [4] to the outputs of the UMTS MILENAGE algorithms.

If there is no desire to retain this compatibility with UMTS MILENAGE used in its 2G mode, a much simpler and more efficient algorithm would be to set TEMP = EKi (RAND), where E is the 128-bit block cipher used as a basic building block in MILENAGE, i.e. TEMP = the result of encrypting RAND using the key K_i; then choose non-overlapping substrings of TEMP to be SRES and K_C, e.g. SRES = TEMP[0]…TEMP[31] and K_C = TEMP[64]…TEMP[127].

This alternative does not form any part of the GSM-MILENAGE algorithms; it is included just for information.