Q (cipher)
Block cipher
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In cryptography, Q is a block cipher invented by Leslie McBride. It was submitted to the NESSIE project, but was not selected.
| General | |
|---|---|
| Designers | Leslie McBride |
| First published | November 2000 |
| Derived from | AES, Serpent |
| Cipher detail | |
| Key sizes | 128, 192, or 256 bits |
| Block sizes | 128 bits |
| Structure | Substitution–permutation network |
| Rounds | 8 or 9 |
| Best public cryptanalysis | |
| A linear attack succeeds with 98.4% probability using 297 known plaintexts.[1] | |
The algorithm uses a key size of 128, 192, or 256 bits. It operates on blocks of 128 bits using a substitution–permutation network structure. There are 8 rounds for a 128-bit key and 9 rounds for a longer key. Q uses S-boxes adapted from Rijndael (also known as AES) and Serpent. It combines the nonlinear operations from these ciphers, but leaves out all the linear transformations except the permutation.[2] Q also uses a constant derived from the golden ratio as a source of "nothing up my sleeve numbers".
Q is vulnerable to linear cryptanalysis; Keliher, Meijer, and Tavares have an attack that succeeds with 98.4% probability using 297 known plaintexts.[1]