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Another recent question on security margin included in its answer the discussion of how many rounds are broken so far. What is the definition of a round?

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up vote 4 down vote accepted

Many block ciphers are defined by specifying a round and then running that specification multiple times. For example, in AES, a round consists of the operations SubBytes, ShiftRows, MixColumns, AddRoundKey. That is one round and, to get AES, you run that multiple times (plus some setup and some post-processing).

Thus a round is defined by each cipher and typically consists of a number of building blocks that are composed together to create a function that is run multiple times.

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