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Q (cipher)

DesignersLeslie McBride
First publishedNovember 2000
Derived fromAES, Serpent
Cipher detail
Key sizes128, 192, or 256 bits
Block sizes128 bits
StructureSubstitution-permutation network
Rounds8 or 9
Best public cryptanalysis
A linear attack succeeds with 98.4% probability using 297 known plaintexts.[1]

In cryptography, Q is a block cipher invented by Leslie McBride. It was submitted to the NESSIE project, but was not selected.

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]


  1. ^ a b L. Keliher, H. Meijer, and S. Tavares (12 September 2001). High probability linear hulls in Q. Proceedings of Second Open NESSIE Workshop. Surrey, England. Retrieved 2018-09-13.CS1 maint: Multiple names: authors list (link)
  2. ^ Eli Biham, Vladimir Furman, Michal Misztal, Vincent Rijmen (11 February 2001). Differential Cryptanalysis of Q. 8th International Workshop on Fast Software Encryption (FSE 2001). Yokohama: Springer-Verlag. pp. 174–186. doi:10.1007/3-540-45473-X_15.CS1 maint: Multiple names: authors list (link)