4 Introductory information

3GPP55.236Release 17Specification of A8_V MILENAGE Algorithm: An example algorithm for the key generation function A8_VTS

4.1 Introduction

For VGCS and VBS ciphering in the GSM system the security function A8_V has been specified. The operation of this function falls completely within the domain of an individual operator, and the function is therefore to be specified by each operator rather than being fully standardized. The algorithm specified in this document is an example that may be used by an operator which does not wish to design its own.

The inputs and outputs of the function A8_V is defined in clause 4.4.

4.2 Notation

4.2.1 Bit/byte ordering

All data variables in this specification are presented with the most significant bit (or byte) on the left hand side and the least significant bit (or byte) on the right hand side. Where a variable is broken down into a number of substrings, the leftmost (most significant) substring is numbered 0, the next most significant is numbered 1, and so on through to the least significant. When a variable, with bit length L, is shown in hexadecimal format, bit 0 is the most significant bit of the leftmost hexadecimal digit, and bit L-1 is the least significant bit of the rightmost hexadecimal digit.

4.2.2 List of symbols

See clause 3.2

4.3 List of variables

For V_Ki, VSTK_RAND and VSTK see TS 43.020 [4]

For all f3-function related variables see TS 35.206 [1]

4.4 Algorithm inputs and outputs

The inputs to the algorithm are given in table 1, the output in table 2 below.

Table 1: Inputs to A8_V

Parameter	Size (bits)	Comment
V_Ki	128	Group key V_Ki[0]…V_Ki[127]
VSTK_RAND	36	Random challenge VSTK_RAND[0]…VSTK_RAND[35]

Table 2: Outputs from A8_V

Parameter	Size (bits)	Comment
VSTK	128	Cipher key VSTK[0]…VSTK[127]