Cost-Effective Architectures for RC5 Brute Force Cracking

J. Buček, J. Hlaváč, M. Matušková, R. Lórencz


In this paper, we discuss the options for brute-force cracking of the RC5 block cipher, that is, for revealing the unknown secret key, given a sample ciphertext and a portion of the corresponding plaintext. First, we summarize the methods employed by the current cracking efforts. Then, we present two hardware architectures for finding the secret key using the “brute force” method. We implement the hardware in FPGA and ASIC and, based on the results, we discuss the cost and time needed to crack the cipher using today’s technology and suggest a minimum key length that can be considered secure. 


RC5 cipher; decryption; brute-force cracking; FPGA; ASIC

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ISSN 1210-2709 (Print)
ISSN 1805-2363 (Online)
Published by the Czech Technical University in Prague