Authentication & Encryption Essay

1329 WordsJul 20, 20116 Pages
Authentication & Encryption Introduction Authentication Procedures Ciphering Procedures Home Introduction Authentication - Whenever a MS requests access to a network, the network must authenticate the MS. Authentication verifies the identity and validity of the SIM card to the network and ensures that the subscriber is authorized access to the network. Encryption - In GSM, encryption refers to the process of creating authentication and ciphering crypto-variables using a special key and an encryption algorithm. Ciphering - Ciphering refers to the process of changing plaintext data into encrypted data using a special key and a special encryption algorithm. Transmissions between the MS and the BTS on the Um link are enciphered. Ki - The Ki is the individual subscriber authentication key. It is a 128-bit number that is paired with an IMSI when the SIM card is created. The Ki is only stored on the SIM card and at the Authentication Center (AuC). The Ki will never be transmitted across the network on any link. RAND - The RAND is a random 128-bit number that is generated by the AuC when the network requests to authenticate a subscriber. The RAND is used to generate the Signed Response (SRES) and Kc crypto-variables. Signed Response - The SRES is a 32-bit crypto-variable used in the authentication process. The MS is challenged by being given the RAND by the network, the SRES is the expected correct response. The MS receives the RAND as a challenge and uses it to calculate the SRES. The SRES is passed up to the network to as a response to the challenge. A3 Algorithm - The A3 algorithm computes a 32-bit Signed Response (SRES). The Ki and RAND are inputted into the A3 algorithm and the result is the 32-bit SRES. The A3 algorithm resides on the SIM card and at the AuC. A8 Algorithm - The A8 algorithm computes a 64-bit ciphering key (Kc).

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