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In cryptography, format-preserving encryption (FPE) refers to encrypting in such a way that the output (the ciphertext) is in the same format as the input (the plaintext). The meaning of "format" varies. Typically only finite domains are discussed, for example: * To encrypt a 16-digit credit card number so that the ciphertext is another 16-digit number. * To encrypt an English word so that the ciphertext is another English word. * To encrypt an n-bit number so that the ciphertext is another n-bit number. (This is the definition of an n-bit block cipher.) For such finite domains, and for the purposes of the discussion below, the cipher is equivalent to a permutation of N integers } where ''N'' is the size of the domain. ==The motivation for FPE== 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「Format-preserving encryption」の詳細全文を読む スポンサード リンク
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