SECURITY OF CIPHERING AND INTEGRITY PROTECTION

A network node of a mobile communications network may need to generate at least one new Input Offset Value, IOV value, for use in protecting communications between the network node and a mobile station. The network node then associates a fresh counter value with the or each new IOV value; calculates a Message Authentication Code based on at least the at least one new IOV value, the fresh counter value associated with the or each new IOV value, and a constant indicating that the Message Authentication Code is calculated to protect the new IOV value; and transmits the at least one new IOV value, the fresh counter value associated with the or each new IOV value, and the calculated Message Authentication Code to the mobile station.