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For example, encryption using an oversimplified three-round cipher can be written as = ((())), where C is the ciphertext and P is the plaintext. Typically, rounds R 1 , R 2 , . . . {\displaystyle R_{1},R_{2},...} are implemented using the same function, parameterized by the round constant and, for block ciphers , the round key from the key ...
c – The length of the key in words (or 1, if b = 0). L[] – A temporary working array used during key scheduling, initialized to the key in words. r – The number of rounds to use when encrypting data. t = 2(r+1) – the number of round subkeys required. S[] – The round subkey words.
In successive rounds, both halves are rotated left by one or two bits (specified for each round), and then 48 round key bits are selected by Permuted Choice 2 (PC-2) – 24 bits from the left half and 24 from the right. The rotations have the effect that a different set of bits is used in each round key; each bit is used in approximately 14 out ...
The Advanced Encryption Standard uses a key schedule to expand a short key into a number of separate round keys. The three AES variants have a different number of rounds. Each variant requires a separate 128-bit round key for each round plus one more. [note 1] The key schedule produces the needed round keys from the initial key.
[1] A P-box is a permutation of all the bits: it takes the outputs of all the S-boxes of one round, permutes the bits, and feeds them into the S-boxes of the next round. A good P-box has the property that the output bits of any S-box are distributed to as many S-box inputs as possible.
Serpent is a symmetric key block cipher that was a finalist in the Advanced Encryption Standard (AES) contest, in which it ranked second to Rijndael. [2] Serpent was designed by Ross Anderson, Eli Biham, and Lars Knudsen. [3] Like other AES submissions, Serpent has a block size of 128 bits and supports a key size of 128, 192, or 256 bits. [4]
Camellia is a Feistel cipher with either 18 rounds (when using 128-bit keys) or 24 rounds (when using 192- or 256-bit keys). Every six rounds, a logical transformation layer is applied: the so-called "FL-function" or its inverse. Camellia uses four 8×8-bit S-boxes with input and output affine transformations and logical operations.
This builds on an attack due to Michael Vielhaber that breaks 576 initialization rounds in only 2 12.3 steps. [ 6 ] Another attack recovers the internal state (and thus the key) of the full cipher in around 2 89.5 steps (where each step is roughly the cost of a single trial in exhaustive search). [ 7 ]