An Improved Hardware Implementation of the Grain Stream Cipher

A common approach to protect confidential information is to use a stream cipher which combines plain text bits with a pseudo-random bit sequence. Among the existing stream ciphers, Non-Linear Feedback Shift Register (NLFSR)-based ones provide the best trade-off between cryptographic security and hardware efficiency. In this paper, we show how to further improve the hardware efficiency of the Grain stream cipher. By transforming the NLFSR of Grain from its original Fibonacci configuration to the Galois configuration and by introducing new hardware solutions, we double the throughput of the 80 and 128-bit key 1 bit/cycle architectures of Grain with no area and power penalty.