block

In cryptography, a block cipher is a deterministic algorithm operating on fixed-length groups of bits, called blocks. It uses an unvarying transformation, that is, it uses a symmetric key. They are specified elementary components in the design of many cryptographic protocols. They, are widely used to implement encryption of large amounts of data, including in data exchange protocols.
Even a secure block cipher is suitable only for the encryption of a single block of data at a time, using a fixed key. A multitude of modes of operation have been designed to allow their repeated use in a secure way, to achieve the security goals of confidentiality and authenticity. However, block ciphers may also feature as building blocks in other cryptographic protocols, such as universal hash functions and pseudo-random number generators.

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