cryptography Cryptography, or cryptology (from "hidden, secret"; and ''graphein'', "to write", or ''-logy, -logia'', "study", respectively), is the practice and study of techniques for secure communication in the presence of Adversary (cryptography), ...

, CIPHERUNICORN-A is a

block cipher In cryptography, a block cipher is a deterministic algorithm that operates on fixed-length groups of bits, called ''blocks''. Block ciphers are the elementary building blocks of many cryptographic protocols. They are ubiquitous in the storage a ...

created by

NEC is a Japanese multinational information technology and electronics corporation, headquartered at the NEC Supertower in Minato, Tokyo, Japan. It provides IT and network solutions, including cloud computing, artificial intelligence (AI), Inte ...

in 2000. It was among the cryptographic techniques recommended for Japanese government use by

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. It is comparable in many respects to the European Union's NESSI ...

in 2003. However, it has been dropped to "candidate" level by the CRYPTREC revision of 2013. The algorithm uses a 16-round

Feistel network In cryptography, a Feistel cipher (also known as Luby–Rackoff block 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 researc ...

structure similar to its predecessor,

CIPHERUNICORN-E In cryptography, CIPHERUNICORN-E is a block cipher created by NEC in 1998. It was among the cryptographic techniques recommended for Japanese government use by CRYPTREC in 2003. However, it has been dropped to "candidate" level by the CRYPTREC rev ...

, but with significant changes. The block size is 128 bits, with

key size In cryptography, key size or key length refers to the number of bits in a key used by a cryptographic algorithm (such as a cipher). Key length defines the upper-bound on an algorithm's security (i.e. a logarithmic measure of the fastest known a ...

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 four 8×8-bit

S-boxes In cryptography, an S-box (substitution-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, thus ensuring Sha ...

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 two of the S-boxes. In contrast to CIPHERUNICORN-E, subkeys are included only at the beginning of each main round. The

key schedule In cryptography, the so-called product ciphers are a certain kind of cipher, where the (de-)ciphering of data is typically done as an iteration of '' rounds''. The setup for each round is generally the same, except for round-specific fixed va ...

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 In cryptography, linear cryptanalysis is a general form of cryptanalysis based on finding affine Affine may describe any of various topics concerned with connections or affinities. It may refer to: * Affine, a Affinity_(law)#Terminology, relat ...

References

External links

256bit Ciphers - CIPHERUNICORN Reference implementation and derived code
{{Cryptography navbox , block Feistel ciphers