Section: 4.4.3.3 Integrity protection and verification
Content: The sender shall use its locally stored NAS COUNT as input to the integrity protection algorithm. The receiver shall use the NAS sequence number included in the received message (or estimated from the 5 bits of the NAS sequence number received in the message) and an estimate for the NAS overflow counter as defined in clause 4.4.3.1 to form the NAS COUNT input to the integrity verification algorithm. The algorithm to calculate the integrity protection information is specified in 3GPP TS 33.401[ 3GPP System Architecture Evolution (SAE); Security architecture ]  [19], and the integrity protection shall include octets 6 to n of the security protected NAS message, i.e. the sequence number IE and the NAS message IE. The integrity protection of the SERVICE REQUEST message is defined in clause 9.9.3.28. In addition to the data that is to be integrity protected, the constant BEARER ID, DIRECTION bit, NAS COUNT and NAS integrity key are input to the integrity protection algorithm. These parameters are described in 3GPP TS 33.401[ 3GPP System Architecture Evolution (SAE); Security architecture ]  [19]. After successful integrity protection validation, the receiver shall update its corresponding locally stored NAS COUNT with the value of the estimated NAS COUNT for this NAS message. Integrity verification is not applicable when EIA0 is used.