Q (cipher)
Encyclopedia
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. Q also uses a constant derived from the golden ratio
as a source of "nothing up my sleeve number
s".
Q is vulnerable to linear cryptanalysis
; Keliher, Meijer, and Tavares have an attack that succeeds with 98.4% probability using 297 known plaintexts.
Cryptography
Cryptography is the practice and study of techniques for secure communication in the presence of third parties...
, Q is a block cipher
Block cipher
In cryptography, a block cipher is a symmetric key cipher operating on fixed-length groups of bits, called blocks, with an unvarying transformation. A block cipher encryption algorithm might take a 128-bit block of plaintext as input, and output a corresponding 128-bit block of ciphertext...
invented by Leslie McBride. It was submitted to the NESSIE
NESSIE
NESSIE was a European research project funded from 2000–2003 to identify secure cryptographic primitives. The project was comparable to the NIST AES process and the Japanese Government-sponsored CRYPTREC project, but with notable differences from both...
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
Substitution-permutation network
In cryptography, an SP-network, or substitution-permutation network , is a series of linked mathematical operations used in block cipher algorithms such as AES .Other ciphers that use SPNs are 3-Way, SAFER, SHARK, and Square....
structure. There are 8 rounds for a 128-bit key and 9 rounds for a longer key. Q uses S-boxes
Substitution box
In cryptography, an S-Box is a basic component of symmetric key algorithms which performs substitution. In block ciphers, they are typically used to obscure the relationship between the key and the ciphertext — Shannon's property of confusion...
adapted from Rijndael (also known as AES) and Serpent
Serpent (cipher)
Serpent is a symmetric key block cipher which was a finalist in the Advanced Encryption Standard contest, where it came second to Rijndael. Serpent was designed by Ross Anderson, Eli Biham, and Lars Knudsen....
. It combines the nonlinear operations from these ciphers, but leaves out all the linear transformations except the permutation. Q also uses a constant derived from the golden ratio
Golden ratio
In mathematics and the arts, two quantities are in the golden ratio if the ratio of the sum of the quantities to the larger quantity is equal to the ratio of the larger quantity to the smaller one. The golden ratio is an irrational mathematical constant, approximately 1.61803398874989...
as a source of "nothing up my sleeve number
Nothing up my sleeve number
In cryptography, nothing up my sleeve numbers are any numbers which, by their construction, are above suspicion of hidden properties. They are used in creating cryptographic functions such as hashes and ciphers. These algorithms often need randomized constants for mixing or initialization purposes...
s".
Q is vulnerable to linear cryptanalysis
Linear cryptanalysis
In cryptography, linear cryptanalysis is a general form of cryptanalysis based on finding affine approximations to the action of a cipher. Attacks have been developed for block ciphers and stream ciphers...
; Keliher, Meijer, and Tavares have an attack that succeeds with 98.4% probability using 297 known plaintexts.