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While researching error-correcting codes in 1990, Matsui was inspired by Eli Biham and Adi Shamir's differential cryptanalysis, and discovered the technique of linear cryptanalysis, published in 1993. Differential and linear cryptanalysis are the two major general techniques known for the cryptanalysis of block ciphers.
For his achievements, Matsui got the 2012 RSA Conference Award for Excellence in Mathematics.