Methods, systems, and computer programs for performing key agreement operations in a communication system are described. In some aspects, a wireless network operator accesses a secret key associated with a mobile device. A key derivation function (KDF) is evaluated based on the secret key to produce a key derivation key, and the KDF is evaluated based on the key derivation key to produce an output value. A session key and a challenge value are obtained based on the output value. In some aspects, the mobile device receives the challenge value and accesses a secret key. A KDF is evaluated based on the secret key to produce a key derivation key, and the KDF is evaluated based on the key derivation key to produce an output value. A response value and a session key are obtained based on the output value. The response value is transmitted to the wireless network operator.