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A Feistel network uses a round function, a function which takes two inputs – a data block and a subkey – and returns one output of the same size as the data block. [1] In each round, the round function is run on half of the data to be encrypted, and its output is XORed with the other half of the data.
Since a single round is usually cryptographically weak, many attacks that fail to work against the full version of ciphers will work on such reduced-round variants. The result of such attack provides valuable information about the strength of the algorithm, [9] a typical break of the full cipher starts out as a success against a reduced-round ...
The Lai-Massey Scheme is similar to a Feistel network in design, but in addition to using a using a non-invertible round function whose input and output is half the data block size, each round uses a full-width invertible half-round function. Either, or preferably both of the functions may take a key input as well.
Many modern block ciphers and hashes are ARX algorithms—their round function involves only three operations: (A) modular addition, (R) rotation with fixed rotation amounts, and (X) XOR. Examples include ChaCha20, Speck, XXTEA, and BLAKE. Many authors draw an ARX network, a kind of data flow diagram, to illustrate such a round function. [22]
Speck supports a variety of block and key sizes. A block is always two words, but the words may be 16, 24, 32, 48 or 64 bits in size. The corresponding key is 2, 3 or 4 words. The round function consists of two rotations, adding the right word to the left word, xoring the key into the left word, then xoring the left word into the right word.
The cipher uses a block size of 128 bits, and a very large key size of 2048 bits. Like DES it has a 16-round Feistel network structure. The round function uses two fixed 4×4-bit S-boxes, chosen to be non-affine. The key is also treated as an 8×8-bit lookup table, using the first bit of each of the 8 bytes of the half-block as input.
WASHINGTON (Reuters) -The Justice Department late on Wednesday asked a U.S. appeals court to reject an emergency bid by TikTok to temporarily block a law that would require its Chinese parent ...
Rounding to a specified power is very different from rounding to a specified multiple; for example, it is common in computing to need to round a number to a whole power of 2. The steps, in general, to round a positive number x to a power of some positive number b other than 1, are: