In cryptography

Cryptography

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

, CIKS-1 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 2002 by A.A. Moldovyan and N.A. Moldovyan. Like its predecessor, Spectr-H64

Spectr-H64

In cryptography, Spectr-H64 is a block cipher designed in 2001 by N. D. Goots, A. A. Moldovyan and N. A. Moldovyan. It relies heavily on the permutation of individual bits, so is much better suited to implementation in hardware than in software....

, it relies heavily on 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...

s of bits, so is 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. It uses an 8 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"...

. In each round the 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...

 also undergoes a transformation dependent on the data. CIKS-1 uses four types of operations: data-dependent permutations, fixed permutations, XORs, and addition mod 4

Modular arithmetic

In mathematics, modular arithmetic is a system of arithmetic for integers, where numbers "wrap around" after they reach a certain value—the modulus....

.

The designers of CIKS-1 didn't specify any key schedule

Key schedule

[[Image:DES-key-schedule.png|thumbnail|220px|The key schedule of DES [[Image:DES-key-schedule.png|thumbnail|220px|The key schedule of DES [[Image:DES-key-schedule.png|thumbnail|220px|The key schedule of DES ("[[Image:DES-key-schedule.png|thumbnail|220px|The key schedule of DES ("...

 for the cipher, but it uses a total 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. Kidney, Heys, and Norvell showed that round keys of low Hamming weight

Hamming weight

The Hamming weight of a string is the number of symbols that are different from the zero-symbol of the alphabet used. It is thus equivalent to the Hamming distance from the all-zero string of the same length. For the most typical case, a string of bits, this is the number of 1's in the string...

 are relatively weak

Weak key

In cryptography, a weak key is a key, which, used with a specific cipher, makes the cipher behave in some undesirable way. Weak keys usually represent a very small fraction of the overall keyspace, which usually means that, if one generates a random key to encrypt a message, weak keys are very...

, so keys should be chosen carefully. The same researchers have also proposed a differential cryptanalysis

Differential cryptanalysis

Differential cryptanalysis is a general form of cryptanalysis applicable primarily to block ciphers, but also to stream ciphers and cryptographic hash functions. In the broadest sense, it is the study of how differences in an input can affect the resultant difference at the output...

of CIKS-1 which uses 2⁵⁶ chosen plaintexts.