Plaintext

In cryptography, plaintext is information a sender wishes to transmit to a receiver. Cleartext is often used as a synonym. Before the computer era, plaintext most commonly meant message text in the language of the communicating parties. 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').

Since computers became commonly available, the definition has also encompassed not only electronic representations of the traditional text, for instance, messages (e.g., email) and document content (e.g., word processor files), but also the computer representations of sound (e.g., speech or music), images (e.g., photos or videos), ATM and credit card transaction information, sensor data, and so forth. Few of these are directly meaningful to humans, being already transformed into computer manipulable forms. Basically, 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.