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 adver ...

, CAST-128 (alternatively CAST5) 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 ...

used in a number of products, notably as the default

cipher In cryptography, a cipher (or cypher) is an algorithm for performing encryption or decryption—a series of well-defined steps that can be followed as a procedure. An alternative, less common term is ''encipherment''. To encipher or encode i ...

in some versions of GPG and

PGP PGP or Pgp may refer to: Science and technology * P-glycoprotein, a type of protein * Pelvic girdle pain, a pregnancy discomfort * Personal Genome Project, to sequence genomes and medical records * Pretty Good Privacy, a computer program for the ...

. It has also been approved for

Government of Canada The government of Canada (french: gouvernement du Canada) is the body responsible for the federal administration of Canada. A constitutional monarchy, the Crown is the corporation sole, assuming distinct roles: the executive, as the ''Crown ...

use by the

Communications Security Establishment The Communications Security Establishment (CSE; french: Centre de la sécurité des télécommunications, ''CST''), formerly (from 2008-2014) called the Communications Security Establishment Canada (CSEC), is the Government of Canada's national c ...

. The algorithm was created in 1996 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 the ...

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 Are ...

using the CAST design procedure. Another member of the CAST family of ciphers, CAST-256 (a former AES candidate) was derived from CAST-128. According to some sources, the CAST name is based on the

initials In a written or published work, an initial capital, also referred to as a drop capital or simply an initial cap, initial, initcapital, initcap or init or a drop cap or drop, is a letter at the beginning of a word, a chapter, or a paragraph that ...

of its inventors, though

Bruce Schneier Bruce Schneier (; born January 15, 1963) is an American cryptographer, computer security professional, privacy specialist, and writer. Schneier is a Lecturer in Public Policy at the Harvard Kennedy School and a Fellow at the Berkman Klein Cente ...

reports the authors' claim that "the name should conjure up images of randomness". CAST-128 is a 12- or 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 research w ...

with a 64-

bit The bit is the most basic unit of information in computing and digital communications. The name is a portmanteau of binary digit. The bit represents a logical state with one of two possible values. These values are most commonly represente ...

block size and a

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 fastest ...

of between 40 and 128 bits (but only in 8-bit increments). The full 16 rounds are used when the

is longer than 80 bits. Components include large 8×32-bit

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 Sha ...

es based on

bent function In the mathematics, mathematical field of combinatorics, a bent function is a special type of Boolean function which is maximally non-linear; it is as different as possible from the set of all linear map, linear and affine functions when measure ...

s, key-dependent rotations,

modular Broadly speaking, modularity is the degree to which a system's components may be separated and recombined, often with the benefit of flexibility and variety in use. The concept of modularity is used primarily to reduce complexity by breaking a sy ...

addition and subtraction, and

XOR Exclusive or or exclusive disjunction is a logical operation that is true if and only if its arguments differ (one is true, the other is false). It is symbolized by the prefix operator J and by the infix operators XOR ( or ), EOR, EXOR, , ...

operations. There are three alternating types of round function, but they are similar in structure and differ only in the choice of the exact operation (addition, subtraction or XOR) at various points. Although

Entrust Entrust Corp., formerly Entrust Datacard, provides software and hardware used to issue financial cards, e-passport production, user authentication for those looking to access secure networks or conduct financial transactions, trust certificat ...

holds a

patent A patent is a type of intellectual property that gives its owner the legal right to exclude others from making, using, or selling an invention for a limited period of time in exchange for publishing an enabling disclosure of the invention."A p ...

on the CAST design procedure, CAST-128 is available worldwide on a

royalty-free Royalty-free (RF) material subject to copyright or other intellectual property rights may be used without the need to pay royalties or license fees for each use, per each copy or volume sold or some time period of use or sales. Computer standard ...

basis for commercial and non-commercial uses.

References

External links

* The CAST-128 Encryption Algorithm * * * {{DEFAULTSORT:Cast-128 Free ciphers Feistel ciphers

See also

References

External links