CIPHERUNICORN-A
Encyclopedia
In cryptography
, CIPHERUNICORN-A is a block cipher
created by NEC
in 2000. It is among the cryptographic techniques recommended for Japanese government use by CRYPTREC
.
The algorithm uses a 16-round Feistel network
structure similar to its predecessor, CIPHERUNICORN-E
, but with significant changes. The block size
is 128 bits, with key size
s of 128, 192, or 256 bits. The round function is even more complicated than that of CIPHERUNICORN-E, but the extra mixing function between rounds has been removed. The round function is still split into two nearly parallel computations; both of these are Feistel networks themselves. The first part (the main stream) is a 10-round Feistel network, using 4 8×8-bit S-boxes
much like the ones from CIPHERUNICORN-E. The last two rounds of the main stream are influenced by the output of the second part (the temporary key generation function). This second, 6-round Feistel network uses modular multiplication
, as well as 2 of the S-boxes. In contrast to CIPHERUNICORN-E, subkeys are added in only at the beginning of each main round.
The key schedule
of CIPHERUNICORN-A makes repeated use of a function called MT, using modular multiplication and all of the S-boxes. A flaw was discovered in the key schedule, such that certain keys are equivalent, but it is unknown just how much of a weakness this is.
The great complexity of CIPHERUNICORN-A's round function has made it difficult to analyze. Some limited analysis has been done on simplified variants, showing that they are likely resistant to both differential
and linear cryptanalysis
.
Cryptography
Cryptography is the practice and study of techniques for secure communication in the presence of third parties...
, CIPHERUNICORN-A 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...
created by NEC
NEC
, a Japanese multinational IT company, has its headquarters in Minato, Tokyo, Japan. NEC, part of the Sumitomo Group, provides information technology and network solutions to business enterprises, communications services providers and government....
in 2000. It is among the cryptographic techniques recommended for Japanese government use by CRYPTREC
CRYPTREC
CRYPTREC is the Cryptography Research and Evaluation Committees set up by the Japanese Government to evaluate and recommend cryptographic techniques for government and industrial use...
.
The algorithm uses a 16-round Feistel network
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...
structure similar to its predecessor, CIPHERUNICORN-E
CIPHERUNICORN-E
In cryptography, CIPHERUNICORN-E is a block cipher created by NEC in 1998. It is among the cryptographic techniques recommended for Japanese government use by CRYPTREC....
, but with significant changes. The 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...
is 128 bits, with 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...
s of 128, 192, or 256 bits. The round function is even more complicated than that of CIPHERUNICORN-E, but the extra mixing function between rounds has been removed. The round function is still split into two nearly parallel computations; both of these are Feistel networks themselves. The first part (the main stream) is a 10-round Feistel network, using 4 8×8-bit 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...
much like the ones from CIPHERUNICORN-E. The last two rounds of the main stream are influenced by the output of the second part (the temporary key generation function). This second, 6-round Feistel network uses modular multiplication
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....
, as well as 2 of the S-boxes. In contrast to CIPHERUNICORN-E, subkeys are added in only at the beginning of each main round.
The 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 ("...
of CIPHERUNICORN-A makes repeated use of a function called MT, using modular multiplication and all of the S-boxes. A flaw was discovered in the key schedule, such that certain keys are equivalent, but it is unknown just how much of a weakness this is.
The great complexity of CIPHERUNICORN-A's round function has made it difficult to analyze. Some limited analysis has been done on simplified variants, showing that they are likely resistant to both differential
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...
and 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...
.