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

, CAST-256 (or CAST6) is a symmetric-key

block cipher In cryptography, a block cipher is a deterministic algorithm operating on fixed-length groups of bits, called ''blocks''. Block ciphers are specified cryptographic primitive, elementary components in the design of many cryptographic protocols and ...

published in June 1998. It was submitted as a candidate for the

Advanced Encryption Standard The Advanced Encryption Standard (AES), also known by its original name Rijndael (), is a specification for the encryption of electronic data established by the U.S. National Institute of Standards and Technology (NIST) in 2001. AES is a variant ...

(AES); however, it was not among the five

AES finalists The Advanced Encryption Standard (AES), the symmetric block cipher ratified as a standard by National Institute of Standards and Technology of the United States (NIST), was chosen using a process lasting from 1997 to 2000 that was markedly more ...

. It is an extension of an earlier cipher,

CAST-128 In cryptography, CAST-128 (alternatively CAST5) is a symmetric-key block cipher used in a number of products, notably as the default cipher in some versions of GPG and PGP. It has also been approved for Government of Canada use by the Communi ...

; both were designed according to the "CAST" design methodology invented by

Carlisle Adams Carlisle M. Adams is a Canadian cryptographer and computer security researcher. Formerly senior cryptographer at Entrust, he is currently a professor at the University of Ottawa. His notable work includes the design (with Stafford Tavares) of t ...

and

Stafford Tavares Stafford Emanuel Tavares is a Canadian cryptographer, professor emeritus at Queen's University. His notable work includes the design (with Carlisle Adams) of the block ciphers CAST-128 and CAST-256. He also helped organize the first Selected Ar ...

Howard Heys Howard M. Heys is a cryptographer, a professor of Electrical and Computer Engineering at Memorial University of Newfoundland. His research includes the design and analysis of stream and block ciphers and efficient hardware implementations of them; ...

and Michael Wiener also contributed to the design. CAST-256 uses the same elements as CAST-128, including

S-box 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 Shan ...

es, but is adapted for a block size of 128 bits – twice the size of its 64-bit predecessor. (A similar construction occurred in the evolution of

RC5 In cryptography, RC5 is a symmetric-key block cipher notable for its simplicity. Designed by Ronald Rivest in 1994, ''RC'' stands for "Rivest Cipher", or alternatively, "Ron's Code" (compare RC2 and RC4). The Advanced Encryption Standard (AES) c ...

into

RC6 In cryptography, RC6 (Rivest cipher 6) is a symmetric key block cipher derived from RC5. It was designed by Ron Rivest, Matt Robshaw, Ray Sidney, and Yiqun Lisa Yin to meet the requirements of the Advanced Encryption Standard (AES) competition. ...

). Acceptable

key size In cryptography, key size, key length, or key space refer 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 fastes ...

s are 128, 160, 192, 224 or 256 bits. CAST-256 is composed of 48 rounds, sometimes described as 12 "quad-rounds", arranged in a generalized

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 research whi ...

. In

RFC RFC may refer to: Computing * Request for Comments, a memorandum on Internet standards * Request for change, change management * Remote Function Call, in SAP computer systems * Rhye's and Fall of Civilization, a modification for Sid Meier's Civ ...

2612, the authors state that, "The CAST-256 cipher described in this document is available worldwide on a royalty-free and licence-free basis for commercial and non-commercial uses." Currently, the best public cryptanalysis of CAST-256 in the standard single secret key setting that works for all keys is the zero-correlation cryptanalysis breaking 28 rounds with 2^246.9 time and 2^98.8 data.

References

External links

CAST-256
by John J. G. Savard

* ttp://www.users.zetnet.co.uk/hopwood/crypto/scan/cs.html Standard Cryptographic Algorithm Naming CAST-256 * Block ciphers {{crypto-stub

See also

References

External links