Modifying authentication techniques in mobile communication systems

Milenage algorithm applies the block cipher Rijnadael (AES) with 128 bit key and 128 bit block size. This algorithm is used in the 3GPP authentication and key generation functions (f1, f1*, f2, f3, f4, f5 and f5*) for mobile communication systems (GSM/UMTS/LTE). In this paper a modification of Milenage algorithm is proposed through a dynamic change of S-box in AES depending on secret key. To get a new secret key for every authentication process we add the random number (RAND) transmitted from the authentication center (AUC) to the contents of the fixed stored secret key (Ki) and thus the initialization of the AES will be different each new authentication process. For every change in secret key a new S-box is derived from the standard one by permuting its rows and columns with the help of a new designed PN sequence generator. A complete simulation of modified Milenage and PN sequence generator is done using Microcontroller (PIC18F452). Security analysis is applied using Avalanche test to compare between the original and modified Milenage. Tests proved that the modified algorithm is more secure than the original one due to the dynamic behavior of S-box with every change of the secret key and immunity against linear and differential cryptanalysis using Avalanche tests. This makes the modified Milenage more suitable for the applications of authentication techniques specially for mobile communication systems.