No abstract

KASUMI is an eight-round Fiestel network that produces 64-bit output data from 64-bit input data using a 128-bit key. Three functions, FL, FO, FI , are involved in each round and each function has its respective keys KL, KO, KI. This work proposed the modifications in existing KASUMI block cipher, which can reduce time delay for generating 64-bit encrypted data. Also, we proposed a modification in FL functions: FL(a) and FL(b) of the existing KASUMI block cipher. Rijndael's 32-bit S-box is introduced in FL (a) function of standard FL function so that it can only work with 16-bit data. The second modification is introduced in the FL(b) function by adding a third stage where XOR and shift operations are involved before the final concatenation of two 16-bit data inside the standard FL function. In addition, the FI function uses S7 and S9 tables only one time instead of two times in the existing KASUMI block cipher, which leads to reduce the overall time delay. The performance improvement of the proposed algorithm over the conventional algorithm is verified by simulation results.

ZUC is stream-cipher which generates 32-bit key-stream by using 128-bit initial key and 123-bit initial vector. It encrypts the plaintext data to produce cipher-text data. The 128-EEA3 encryption and 128-EIA3 authentication algorithms are based on ZUC which are specified for use in 3GPP cellular communications systems. The algorithm is divided in three stages: LFSR (Linear Feedback Shift Register), Bit Reorganization (BR) and, Non-Linear Function. In this paper, we are going to discuss about our modifications proposed for LFSR along with small change in operation of Non-linear Function which can reduce time for generating key-stream. Many attacks based on weakness of LFSR due to its linearity are proposed which in turn makes ZUC susceptible to various attacks based on LFSR. As we know in the structure of LFSR, non-linearity is provided in last block of LFSR by feedback operation while all other being clocked with previous value of LFSR, so we have introduced bit-shifting and circular shift operations on few blocks of LFSR output of which will be taken as input to other blocks of LFSR.