In cryptography, a block cipher is a deterministic algorithm operating on fixed-length groups of bits, called a block, with an unvarying transformation that is specified by a symmetric key. Block ciphers operate as important elementary components in the design of many cryptographic protocols, and are widely used to implement encryption of bulk data.
In cryptography, a cipher 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 is to convert information into cipher or code. In common parlance, "cipher" is synonymous with "code", as they are both a set of steps that encrypt a message; however, the concepts are distinct in cryptography, especially classical cryptography.
In cryptography, the one-time pad (OTP) is an encryption technique that cannot be cracked, but requires the use of a one-time pre-shared key the same size as, or longer than, the message being sent. In this technique, a plaintext is paired with a random secret key. Then, each bit or character of the plaintext is encrypted by combining it with the corresponding bit or character from the pad using modular addition. If the key is (1) truly random, (2) at least as long as the plaintext, (3) never reused in whole or in part, and (4) kept completely secret, then the resulting ciphertext will be impossible to decrypt or break. It has also been proven that any cipher with the perfect secrecy property must use keys with effectively the same requirements as OTP keys. Digital versions of one-time pad ciphers have been used by nations for some critical diplomatic and military communication, but the problems of secure key distribution have made them impractical for most applications.
In cryptography, a Caesar cipher, also known as Caesar's cipher, the shift cipher, Caesar's code or Caesar shift, is one of the simplest and most widely known encryption techniques. It is a type of substitution cipher in which each letter in the plaintext is replaced by a letter some fixed number of positions down the alphabet. For example, with a left shift of 3, D would be replaced by A, E would become B, and so on. The method is named after Julius Caesar, who used it in his private correspondence.
A stream cipher is a symmetric key cipher where plaintext digits are combined with a pseudorandom cipher digit stream (keystream). In a stream cipher, each plaintext digit is encrypted one at a time with the corresponding digit of the keystream, to give a digit of the ciphertext stream. Since encryption of each digit is dependent on the current state of the cipher, it is also known as state cipher. In practice, a digit is typically a bit and the combining operation an exclusive-or (XOR).
Symmetric-key algorithms are algorithms for cryptography that use the same cryptographic keys for both encryption of plaintext and decryption of ciphertext. The keys may be identical or there may be a simple transformation to go between the two keys. The keys, in practice, represent a shared secret between two or more parties that can be used to maintain a private information link. This requirement that both parties have access to the secret key is one of the main drawbacks of symmetric key encryption, in comparison to public-key encryption.
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 open and transparent than its predecessor, the Data Encryption Standard (DES). This process won praise from the open cryptographic community, and helped to increase confidence in the security of the winning algorithm from those who were suspicious of backdoors in the predecessor, DES.
4DTV is a proprietary broadcasting standard and technology for digital cable broadcasting and C-band/Ku-band satellite dishes from Motorola, using General Instrument's DigiCipher II for encryption. It can tune in both analog VideoCipher 2 and digital DCII satellite channels.
DigiCipher 2, or simply DCII, is a proprietary standard format of digital signal transmission and it doubles as an encryption standard with MPEG-2/MPEG-4 signal video compression used on many communications satellite television and audio signals. The DCII standard was originally developed in 1997 by General Instrument, which then became the Home and Network Mobility division of Motorola, then bought by Google in Aug 2011, and lastly became the Home portion of the division to Arris.
Advanced Systems Format is Microsoft's proprietary digital audio/digital video container format, especially meant for streaming media. ASF is part of the Media Foundation framework.
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. Both the input (plaintext) and output (ciphertext) are the same length; the output cannot be shorter than the input – this follows logically from the pigeonhole principle and the fact that the cipher must be reversible – and it is undesirable for the output to be longer than the input.
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 (USA); it is also commonly known as a Feistel network. A large proportion of block ciphers use the scheme, including the Data Encryption Standard (DES). The Feistel structure has the advantage that encryption and decryption operations are very similar, even identical in some cases, requiring only a reversal of the key schedule. Therefore, the size of the code or circuitry required to implement such a cipher is nearly halved.
A codebook is a type of document used for gathering and storing codes. Originally codebooks were often literally books, but today codebook is a byword for the complete record of a series of codes, regardless of physical format.
In cryptography, MMB is a block cipher designed by Joan Daemen as an improved replacement for the IDEA cipher. Modular multiplication is the central element in the design. Weaknesses in the key schedule were identified by Eli Biham, and this, together with the cipher's not having been designed to resist linear cryptanalysis, meant that other designs were pursued instead, such as 3-Way.
In cryptography, FROG is a block cipher authored by
Georgoudis, Leroux and Chaves. The algorithm can work with any block size between 8 and 128 bytes, and supports key sizes between 5 and 125 bytes. The algorithm consists of 8 rounds and has a very complicated key schedule.
The Hasty Pudding Cipher (HPC) is a variable-block-size block cipher designed by Richard Schroeppel, which was an unsuccessful candidate in the competition for selecting the U.S. Advanced Encryption Standard (AES). It has a number of unusual properties for a block cipher: its input block size and key length are variable, and it includes an additional input parameter called the "spice" for use as a secondary, non-secret key. The Hasty Pudding cipher was the only AES candidate designed exclusively by U.S. cryptographers.
In cryptography, Hierocrypt-L1 and Hierocrypt-3 are block ciphers created by
Toshiba in 2000. They were submitted to the NESSIE project, but were not selected. Both
algorithms were among the cryptographic techniques recommended for Japanese government use by CRYPTREC in 2003, however, both have been dropped to "candidate" by CRYPTREC revision in 2013.
Cryptography or cryptology is the practice and study of techniques for secure communication in the presence of third parties called adversaries. More generally, cryptography is about constructing and analyzing protocols that prevent third parties or the public from reading private messages; various aspects in information security such as data confidentiality, data integrity, authentication, and non-repudiation are central to modern cryptography. Modern cryptography exists at the intersection of the disciplines of mathematics, computer science, electrical engineering, communication science, and physics. Applications of cryptography include electronic commerce, chip-based payment cards, digital currencies, computer passwords, and military communications.
In cryptography, format-preserving encryption (FPE), refers to encrypting in such a way that the output is in the same format as the input. The meaning of "format" varies. Typically only finite domains are discussed, for example:
