Cryptographic Functions A3, A8 and A5in GSM Protocol

The components A3 , A8 , and A5.

• A3 : one-way function.

• A8 : one-way function.

• A5 : one-way encryption/decryption algorithm using Kc.

A5/1: Western Europe, A5/2: other countries (GSM MoU is attempting to establish

A5/2 as the global standard)

A3

A8

A5/2

SRES

(32 bits)

RAND

(128 bits)

Ki

(128 bits)

Kc(64 bits)

Authentication

Privacy

TDMA Frame

No. (22 bits)

Data Stream

(114 bits)

Ciphertext

114 bits

• The repeated cycle of TDMA Frame No. is 3 hrs 28 min 53 sec 760 msec (Range: 0~2,715,647).

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