Topics in Cryptology — CT-RSA 2002

We investigate a known plaintext attack on RC5 based on correlations. Compared with the best previous known-plaintext attack on RC5-32, a linear cryptanalysis by Borst, Preneel, and Vandewalle, our attack applies to a larger number of rounds. RC5-32 with r rounds can be broken with a success probability of 90% by using 2^<6.14r+2.27> plaintexts. Therefore, our attack can break RC5-32 with 10 rounds (20 half-rounds) with 2^<63.67> plaintexts with a probability of 90%. With a success probability of 30%, our attack can break RC5-32 with 21 halfrounds by using 2^<63.07> plaintexts.Topics in cryptology - CT-RSA 2002 : The Cryptographers' Track at the RSA Conference 2002, San Jose, CA, USA, February, 18-22, 2002 : proceedings / Bart Preneel (ed.)