In cryptography

Cryptography

Cryptography is the practice and study of techniques for secure communication in the presence of third parties...

, SHARK 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...

 identified as one of the predecessors of Rijndael (the Advanced Encryption Standard

Advanced Encryption Standard

Advanced Encryption Standard is a specification for the encryption of electronic data. It has been adopted by the U.S. government and is now used worldwide. It supersedes DES...

).

SHARK has a 64-bit block size

Block size (cryptography)

In modern cryptography, symmetric key ciphers are generally divided into stream ciphers and block ciphers. Block ciphers operate on a fixed length string of bits. The length of this bit string is the block size...

 and a 128-bit key size

Key size

In cryptography, key size or key length is the size measured in bits of the key used in a cryptographic algorithm . An algorithm's key length is distinct from its cryptographic security, which is a logarithmic measure of the fastest known computational attack on the algorithm, also measured in bits...

. It is a six round SP-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....

 which alternates a key

Key (cryptography)

In cryptography, a key is a piece of information that determines the functional output of a cryptographic algorithm or cipher. Without a key, the algorithm would produce no useful result. In encryption, a key specifies the particular transformation of plaintext into ciphertext, or vice versa...

 mixing stage with linear and non-linear transformation layers. The linear transformation uses an MDS matrix

MDS matrix

An MDS matrix is a matrix representing a function with certain diffusion properties that have useful applications in cryptography...

 representing a Reed-Solomon error correcting code in order to guarantee good diffusion

Confusion and diffusion

In cryptography, confusion and diffusion are two properties of the operation of a secure cipher which were identified by Claude Shannon in his paper Communication Theory of Secrecy Systems, published in 1949....

. The nonlinear layer is composed of eight 8×8-bit S-boxes based on the function F(x) = x⁻¹ over GF(2⁸).

Five rounds of a modified version of SHARK can be broken using an interpolation attack

Interpolation attack

In cryptography, an interpolation attack is a type of cryptanalytic attack against block ciphers.In the attack, an algebraic function is used to represent an S-box. This may be a simple quadratic, or a polynomial or rational function over a Galois field. Its coefficients can be determined by...

(Jakobsen and Knudsen, 1997).

External links

• SCAN's entry for SHARK