In cryptography

Cryptography

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

, Spectr-H64 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...

 designed in 2001 by N. D. Goots, A. A. Moldovyan and N. A. Moldovyan. It relies heavily on the permutation

Permutation

In mathematics, the notion of permutation is used with several slightly different meanings, all related to the act of permuting objects or values. Informally, a permutation of a set of objects is an arrangement of those objects into a particular order...

 of individual bits, so is much better suited to implementation in hardware than in software.

The algorithm has a 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...

 of 64 bits and 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...

 of 256 bits. It uses a 12 round structure in which half of the block determines the transformation of the other half in each round, similar to a Feistel cipher

Feistel cipher

In cryptography, a Feistel cipher is a symmetric structure used in the construction of block ciphers, named after the German-born physicist and cryptographer Horst Feistel who did pioneering research while working for IBM ; it is also commonly known as a Feistel network. A large proportion of block...

 or RC5

RC5

In cryptography, RC5 is a block cipher notable for its simplicity. Designed by Ronald Rivest in 1994, RC stands for "Rivest Cipher", or alternatively, "Ron's Code"...

. This same basic design was repeated in its successor, CIKS-1

CIKS-1

In cryptography, CIKS-1 is a block cipher designed in 2002 by A.A. Moldovyan and N.A. Moldovyan. Like its predecessor, Spectr-H64, it relies heavily on permutations of bits, so is better suited to implementation in hardware than in software....

.

Cryptanalysis

An analysis of Spectr-H64 was presented in 2002 by Selçuk Kavut and Melek D. Yücel of the Middle East Technical University, showing a method of using a differential attack to retrieve half of the key bits when a single round is used. Using this method, they then presented a slide attack

Slide attack

The slide attack is a form of cryptanalysis designed to deal with the prevailing idea that even weak ciphers can become very strong by increasing the number of rounds, which can ward off a differential attack. The slide attack works in such a way as to make the number of rounds in a cipher irrelevant...

that requires 2¹⁷ chosen plaintexts to return all key bits on the full 12 rounds.