Question

Which of the following cannot be kept proprietary by the GSM operator?
A3
A5
A8
All of the above

Can you provide an explanation

Answer 1

Answer.....

GSM stands for Global System for Mobile Communications. It is an open & digital cellular technology used mainly for transmitting mobile voice & data service. GSM uses three different security algorithm called A3, A5, A8.

Every GSM mobile phone has a subscriber identity module (SIM). It is operator dependent smart card which contains A3 & A8 algorithms, IMSI (International Mobile Subscriber Identity) and the authentication key (Ki). The different security algorithm (A3, A5, A8) are programmed into the SIM by the GSM operator at the time of service provisioning the IMSI.

A3 algorithm:- It is a symmetric algorithm used to authenticate each mobile by verifying the user password with the cryptographic key.

A8 algorithm:- cipher key generation algorithm used for ciphering the key. GSM makes use of a ciphering key to protect both user data and signalling on the vulnerable air interface & the algorithm is stored on the SIM card.

A5 algorithm:- ciphering algorithm used for encryption. The A5 algorithm is implemented in the hardware of the mobile phone. A8 algorithm is then along with A5 algorithm is used to encipher or decipher the data. A5 algorithm needs to be used across all GSM network operators.

Both A3 & A8 algorithm are kept and implemented in subscriber identity module. A3 & A8 are different for different network.

Here all the above (A3, A5, A8) cannot be kept proprietary by the GSM operator & none of the algorithms are published by GSM Association. All are discovered by using reverse engineering methods.