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In cryptography, plaintext is information a sender wishes to transmit to a receiver. ''Cleartext'' is often used as a synonym. Plaintext has reference to the operation of cryptographic algorithms, usually encryption algorithms, and is the input upon which they operate. ''Cleartext'', by contrast, refers to data that is transmitted or stored unencrypted (that is, 'in the clear'). ==Overview== Before the computer era, plaintext most commonly meant message text in the language of the communicating parties. Since computers became commonly available, the definition has expanded to include: * messages (for example, email messages) * document content such as word processor and spreadsheet files * audio and video files, digital photographs and any other multimedia * files containing other files such as Zip files or ISO images * ATM, credit card and other banking information * sensor data * any other data that a person wishes to keep private Much of this data is not directly meaningful to humans, being already transformed into computer manipulable forms. While the original definition implied that the message could be read by a human being, the modern definition emphasizes that a person using a computer could easily interpret the data. Any information which the communicating parties wish to conceal from others can now be treated, and referred to, as plaintext. Thus, in a significant sense, plaintext is the 'normal' representation of data before any action has been taken to conceal, compress, or 'digest' it. It need not represent text, and even if it does, the text may not be "plain". Plaintext is used as input to an encryption algorithm; the output is usually termed ciphertext particularly when the algorithm is a cipher. Codetext is less often used, and almost always only when the algorithm involved is actually a code. In some systems, however, multiple layers of encryption are used, in which case the output of one encryption algorithm becomes plaintext input for the next. 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「plaintext」の詳細全文を読む スポンサード リンク
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