Section: 6.4.3.1 NAS input parameters to integrity algorithm
Content: The input parameters to the NAS 128-bit integrity algorithms as described in Annex D shall be set as follows. The KEY input shall be equal to the KNASint key. The BEARER input shall be equal to the NAS connection identifier. The DIRECTION bit shall be set to 0 for uplink and 1 for downlink. The COUNT input shall be constructed as follows: COUNT := 0x00 || NAS COUNT Where NAS COUNT is the 24-bit NAS UL COUNT or the 24-bit NAS DL COUNT value, depending on the direction, that is associated to the current NAS connection identified by the value used to form the BEARER input. A NAS COUNT shall be constructed as follows: NAS COUNT := NAS OVERFLOW || NAS SQN Where - NAS OVERFLOW is a 16-bit value which is incremented each time the NAS SQN is incremented from the maximum value. - NAS SQN is the 8-bit sequence number carried within each NAS message. The use and mode of operation of the 128-bit integrity algorithms are specified in Annex D.