Key agreement for wireless communication
Methods, systems, and computer programs for performing key agreement operations in a communication system are described. In some aspects, a wireless network operator receives a mobile device identifier and accesses a secret key associated with the mobile device. A message authentication code function is evaluated based on the secret key to produce an output value. A session key and a challenge value are obtained based on the output value. In some aspects, a mobile device accesses a secret key in response to receiving the challenge value from the wireless network operator. A message authentication code function is evaluated based on the secret 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.
1. A method performed by a computer system of a wireless network operator, the method comprising:
the computer system receiving an identifier of a mobile device; the computer system obtaining a challenge:
the computer system accessing, based on the identifier, a secret key stored in a database, the secret key associated with the mobile device;
the computer system evaluating a message authentication code (MAC) function based on the secret key and the challenge to produce an output value;
the computer system obtaining a session key and an expected response based on the output value;
the computer system transmitting a message to the mobile device, the message including the challenge:
the computer system receiving from the mobile device a response generated by the mobile device based on the secret key and the challenge; and
in response to determining that the response received from the mobile device matches the expected response, utilizing a secure communication channel with the mobile device that utilizes the session key.
2. The method of claim 1 , wherein obtaining the session key comprises obtaining a plurality of session keys, and the plurality of session keys include a ciphering key and an integrity key.
3. The method of claim 2 , wherein:
the computer system obtaining the challenge comprising obtaining a random challenge value before evaluating the MAC function;
the method further comprising:
the computer system generating a second message that includes the ciphering key, the integrity key, the random challenge value, and the expected response value; and
the computer system transmitting the second message to a wireless station of a wireless network.
4. The method of claim 1 , wherein the MAC function is evaluated by evaluating a key derivation function (KDF) that includes the MAC function.
5. The method of claim 4 , wherein the KDF is evaluated on a plurality of input values including:
the secret key; and
an output length that specifies a bit-length of the output value.
6. The method of claim 5 , wherein the computer system obtaining the challenge comprises obtaining a random challenge value after receiving the identifier of the mobile device.
7. The method of claim 1 , wherein generating the session key based on the output value includes:
the computer system evaluating the MAC function based on the output value to produce another output value; and
the computer system generating the session key and the expected response based on the other output value.
8. The method of claim 1 , further comprising:
the computer system obtaining a MAC based on the secret key;
the computer system accessing a sequence value associated with the mobile device; and
the computer system generating a server authentication token based on the MAC and the sequence value.
9. A wireless network operator system comprising:
a communication interface operable to receive an identifier of a mobile device, and a response from the mobile device;
data processing apparatus operable to:
obtain a challenge;
access, based on the identifier, a secret key stored in a database, the secret key associated with the mobile device;
evaluate a message authentication code (MAC) function based on the secret key and the challenge to produce an output value;
obtain a session key and an expected response based on the output value;
transmit a message to the mobile device, the message including the challenge;
determine that the response from the mobile device matches the expected response, wherein the response received from the mobile device is based on the secret key and the challenge;
in response to determining that the response received from the mobile device matches the expected response, utilize a secure communication channel with the mobile device that utilizes the session key.
10. The wireless network operator system of claim 9 , wherein obtaining the session key comprises obtaining a plurality of session keys, and the plurality of session keys include a ciphering key and an integrity key.
11. The wireless network operator system of claim 10 , wherein:
obtaining the challenge comprising obtaining a random challenge value before evaluating the MAC function; and
the data processing apparatus is further operable to:
generate a second message that includes the ciphering key, the integrity key, the random challenge value, and the expected response value; and
wherein the communication interface is operable to transmit the second message to a wireless station of a wireless network.
12. The wireless network operator system of claim 9 , wherein the MAC function is evaluated by evaluating a key derivation function (KDF) that includes the MAC function.
13. The wireless network operator system of claim 12 , wherein the KDF is evaluated on a plurality of input values including:
the secret key; and
an output length that specifies a bit-length of the output value.
14. The wireless network operator system of claim 13 , wherein obtaining the random value comprising obtaining a random challenge value.
15. The wireless network operator system of claim 9 , wherein the data processing apparatus is further operable to:
obtain a MAC based on the secret key;
access a sequence value associated with the mobile device; and
generate a server authentication token based on the MAC and the sequence value.
16. A method performed by a mobile device, the method comprising:
the mobile device accessing a secret key in response to receiving a challenge value from a wireless network operator system;
the mobile device evaluating a message authentication code (MAC) function based on the secret key and the challenge value to produce an output value;
the mobile device obtaining a response value and a session key based on the output value; and
the mobile device transmitting the response value to the wireless network operator system;
in response to the wireless network operator system determining that the response value matches an expected response value, utilizing a secure communication channel to communicate with the wireless network operator system, the communication utilizing the session key.
17. The method of claim 16 , wherein obtaining the session key comprises the mobile device obtaining a plurality of session keys, and the plurality of session keys include a ciphering key and an integrity key.
18. The method of claim 16 , wherein the MAC function is evaluated by evaluating a key derivation function (KDF) that includes the MAC function.
19. The method of claim 18 , wherein the KDF is evaluated on a plurality of input values including:
the secret key;
the challenge value; and
an output length that specifies a bit-length of the output value.
20. The method of claim 16 , further comprising:
the mobile device obtaining a MAC based on the secret key and the challenge value;
the mobile device accessing a sequence value previously stored on the mobile device; and
the mobile device generating a mobile device authentication token based on the MAC and the sequence value.