Effective Uses of FPGAs for Brute-Force Attack on RC4 Ciphers

This paper presents an effective field-programmable gate array (FPGA)-based hardware implementation of a parallel key searching system for the brute-force attack on RC4 encryption. The design employs several novel key scheduling techniques to minimize the total number of cycles for each key search and uses on-chip memories of the FPGA to maximize the number of key searching units per chip. Based on the design, a total of 176 RC4 key searching units can be implemented in a single Xilinx XC2VP20-5 FPGA chip, which currently costs only a few hundred U.S. dollars. Operating at a 47-MHz clock rate, the design can achieve a key searching speed of 1.07 x 10⁷ keys per second. Breaking a 40-bit RC4 encryption only requires around 28.5 h.