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Cryptanalysis is the process of analyzing cryptographic messages to reveal their meaning. It is the opposite of cryptography, which is the art of concealing the meaning of messages. The first known work on cryptanalysis was written by the Arab mathematician Al-Kindi in the 9th century. His book, Manuscript on Deciphering Cryptographic Messages, described several techniques for breaking codes and ciphers. These techniques are still used by cryptanalysts today.