Cryptanalysis of a quadratic knapsack cryptosystem

Wang and Hu [B. Wang and Y. Hu, Quadratic compact knapsack public-key cryptosystem, Comput. Math. Appl. 59 (1) (2010) 194–206] proposed a knapsack-type public-key cryptosystem by introducing an easy quadratic compact knapsack problem and then using the Chinese remainder theorem to disguise the easy knapsack instant. In this paper, we present a heuristic stereotyped message attack that allows the cryptanalyst to recover the plaintext message when partial information about the original message is known. In particular, as shown by our experiments, for the proposed system parameter n = 100 which corresponds to a block length of 400 bits, exposing 60% of the plaintext allows the cryptanalyst to recover the remaining 160 bits of the message with a success probability of about 90% in about 2 hours.