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The Solitaire cryptographic algorithm was designed by Bruce Schneier to allow field agents to communicate securely without having to rely on electronics or having to carry incriminating tools, at the request of Neal Stephenson for use in his novel ''Cryptonomicon''. It was designed to be a manual cryptosystem calculated with an ordinary deck of playing cards. In ''Cryptonomicon'', this algorithm was originally called Pontifex to hide the fact that it involved playing cards. One of the motivations behind Solitaire's creation is that in totalitarian environments, a deck of cards is far more affordable (and less incriminating) than a personal computer with an array of cryptological utilities. However, as Schneier warns in the appendix of ''Cryptonomicon'', just about everyone with an interest in cryptanalysis will know about this algorithm. ==Encryption and decryption== The algorithm generates a stream of values which are combined with the message to encrypt and decrypt it. Each value of the keystream is to be used for one value of the message, thus the keystream will need to be the same length as the message. # Remove all punctuation and convert the characters to the same case. # Convert all the characters to their natural numerical values, A = 1, B = 2, etc., Z = 26. # To encrypt a message, add each keystream value to its corresponding character in the plaintext, rolling over back to 1 if the resulting value exceeds 26 (modulo 26 arithmetic). To decrypt, subtract each keystream value from its corresponding character in the ciphertext, rolling back up to 26 if the resulting value should be lower than 1. (In mathematics this is called modular arithmetic.) 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Solitaire (cipher)」の詳細全文を読む スポンサード リンク
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