# REF - Encryption Algorithms

Random number generation. A random number generator (RNG) is a computational or physical device designed to generate a sequence of numbers or symbols that lack any pattern, i.e. appear random. The many applications of randomness have led to the development of several different methods for generating random data. Many of these have existed since ancient times, including dice, coin flipping, the shuffling of playing cards, the use of yarrow stalks (by divination) in the I Ching, and many other techniques. Because of the mechanical nature of these techniques, generating large numbers of sufficiently random numbers (important in statistics) required a lot of work and/or time. Thus, results would sometimes be collected and distributed as random number tables. Nowadays, after the advent of computational random number generators, a growing number of government-run lotteries, and lottery games, are using RNGs instead of more traditional drawing methods.

Practical applications and uses Generation methods Perfect but not Uusable - One-time pad. Excerpt from a one-time pad The "pad" part of the name comes from early implementations where the key material was distributed as a pad of paper, so that the top sheet could be easily torn off and destroyed after use. For ease of concealment, the pad was sometimes reduced to such a small size that a powerful magnifying glass was required to use it. The KGB used pads of such size that they could fit in the palm of one's hand,[8] or in a walnut shell.[9] To increase security, one-time pads were sometimes printed onto sheets of highly flammable nitrocellulose, so that they could be quickly burned after use.

There is some ambiguity to the term because some authors use the terms "Vernam cipher" and "one-time pad" synonymously, while others refer to any additive stream cipher as a "Vernam cipher", including those based on a cryptographically secure pseudorandom number generator (CSPRNG).[10] History of invention The next development was the paper pad system. Example Problems The spooky world of the 'numbers stations' Image copyright Thinkstock This is the era of hyper-tech espionage, encrypted emails and mindboggling cryptography. But you can hear a very old-fashioned form of espionage on shortwave radio. It is 13:03 on a Tuesday in a cramped room with some fairly advanced radio equipment. What is suddenly heard on a shortwave receiving station is a 10-minute message in Morse code. There is a small community of aficionados who believe messages like this are a throwback to the era of Cold War espionage.

They are the mysterious "numbers stations". At the apex of the Cold War, radio lovers across the globe started to notice bizarre broadcasts on the airwaves. Encountering these shortwave radio messages, many radio hams concluded that they were being used to send coded messages across extremely long distances. The Lincolnshire Poacher was so named because of two bars from an English folk song of that name being used as an "interval signal". Media playback is unsupported on your device. Numbers station. A numbers station is a type of shortwave radio station characterized by unusual broadcasts, reading out lists of numbers or incomprehensible morse code messages.[1] The voices are often created by speech synthesis and are transmitted in a wide variety of languages.

The voices are usually female, although sometimes men's or children's voices are used. Some voices are synthesized and created by machines; however, some stations used to have live readers.[2] In June 2003, the United States similarly charged Walter Kendall Myers with conspiracy to spy for Cuba and receiving and decoding messages broadcast from a numbers station operated by the Cuban Intelligence Directorate to further that conspiracy.[10][11] §Suspected origins and use According to the notes of The Conet Project,[14][15] which has compiled recordings of these transmissions, numbers stations have been reported since World War I. If accurate, this would count numbers stations among the earliest radio broadcasts. Usable but not Perfect - Public-key cryptography.

An unpredictable (typically large and random) number is used to begin generation of an acceptable pair of keys suitable for use by an asymmetric key algorithm. In an asymmetric key encryption scheme, anyone can encrypt messages using the public key, but only the holder of the paired private key can decrypt. Security depends on the secrecy of the private key. In the Diffie–Hellman key exchange scheme, each party generates a public/private key pair and distributes the public key. After obtaining an authentic copy of each other's public keys, Alice and Bob can compute a shared secret offline. Public-key cryptography, also known as asymmetric cryptography, is a class of cryptographic algorithms which requires two separate keys, one of which is secret (or private) and one of which is public.

Message authentication involves processing a message with a private key to produce a digital signature. Understanding Description There are two main uses of public-key cryptography: History Advanced Encryption Standard. The Advanced Encryption Standard (AES), also referenced as Rijndael[4][5] (its original name), is a specification for the encryption of electronic data established by the U.S. National Institute of Standards and Technology (NIST) in 2001.[6] AES is based on the Rijndael cipher[5] developed by two Belgian cryptographers, Joan Daemen and Vincent Rijmen, who submitted a proposal to NIST during the AES selection process.[7] Rijndael is a family of ciphers with different key and block sizes. For AES, NIST selected three members of the Rijndael family, each with a block size of 128 bits, but three different key lengths: 128, 192 and 256 bits.

AES has been adopted by the U.S. government and is now used worldwide. It supersedes the Data Encryption Standard (DES),[8] which was published in 1977. The algorithm described by AES is a symmetric-key algorithm, meaning the same key is used for both encrypting and decrypting the data. In the United States, AES was announced by the NIST as U.S. . International Data Encryption Algorithm. In cryptography, the International Data Encryption Algorithm (IDEA), originally called Improved Proposed Encryption Standard (IPES), is a symmetric-key block cipher designed by James Massey of ETH Zurich and Xuejia Lai and was first described in 1991. The algorithm was intended as a replacement for the Data Encryption Standard (DES). IDEA is a minor revision of an earlier cipher, Proposed Encryption Standard (PES).

The cipher was designed under a research contract with the Hasler Foundation, which became part of Ascom-Tech AG. The cipher was patented in a number of countries but was freely available for non-commercial use. The name “IDEA” is also a trademark. The last patents expired in 2012 and IDEA is now patent-free and thus free to use.[2][3] IDEA was used in Pretty Good Privacy (PGP) v2.0, and was incorporated after the original cipher used in v1.0, BassOmatic, was found to be insecure.[4] IDEA is an optional algorithm in the OpenPGP standard. Operation Structure Triple DES. In cryptography, Triple DES (3DES) is the common name for the Triple Data Encryption Algorithm (TDEA or Triple DEA) symmetric-key block cipher, which applies the Data Encryption Standard (DES) cipher algorithm three times to each data block. The original DES cipher's key size of 56 bits was generally sufficient when that algorithm was designed, but the availability of increasing computational power made brute-force attacks feasible.

Triple DES provides a relatively simple method of increasing the key size of DES to protect against such attacks, without the need to design a completely new block cipher algorithm. Definitive standards The Triple Data Encryption Algorithm (TDEA) is defined in each of: Name of the algorithm The Data Encryption Standard (DES) shall consist of the following Data Encryption Algorithm (DES) [sic] and Triple Data Encryption Algorithm (TDEA, as described in ANSI X9.52).

The TDEA is commonly known as Triple DES (Data Encryption Standard). Algorithm Data Encryption Standard. DES is now considered to be insecure for many applications. This is chiefly due to the 56-bit key size being too small; in January, 1999, distributed.net and the Electronic Frontier Foundation collaborated to publicly break a DES key in 22 hours and 15 minutes (see chronology).

There are also some analytical results which demonstrate theoretical weaknesses in the cipher, although they are infeasible to mount in practice. The algorithm is believed to be practically secure in the form of Triple DES, although there are theoretical attacks. In recent years, the cipher has been superseded by the Advanced Encryption Standard (AES).

Furthermore, DES has been withdrawn as a standard by the National Institute of Standards and Technology (formerly the National Bureau of Standards). Some documentation makes a distinction between DES as a standard and DES as an algorithm, referring to the algorithm as the DEA (Data Encryption Algorithm). §History of DES §NSA's involvement in the design and. Serpent (cipher) Serpent is a symmetric key block cipher that was a finalist in the Advanced Encryption Standard (AES) contest, where it was ranked second to Rijndael. Serpent was designed by Ross Anderson, Eli Biham, and Lars Knudsen. The Serpent cipher is in the public domain and has not been patented. There are no restrictions or encumbrances whatsoever regarding its use. As a result, anyone is free to incorporate Serpent in their software (or hardware implementations) without paying license fees.

Rijndael is a substitution-linear transformation network with ten, twelve, or fourteen rounds, depending on the key size, and with block sizes of 128 bits, 192 bits, or 256 bits, independently specified. Serpent is a substitution-permutation network which has thirty-two rounds, plus an initial and a final permutation to simplify an optimized implementation. The XSL attack, if effective, would weaken Serpent (though not as much as it would weaken Rijndael, which became AES). Twofish. Twofish's distinctive features are the use of pre-computed key-dependent S-boxes, and a relatively complex key schedule. One half of an n-bit key is used as the actual encryption key and the other half of the n-bit key is used to modify the encryption algorithm (key-dependent S-boxes).

Twofish borrows some elements from other designs; for example, the pseudo-Hadamard transform (PHT) from the SAFER family of ciphers. Twofish has a Feistel structure like DES. Cryptanalysis In 1999, Niels Ferguson published an impossible differential attack that breaks six rounds out of 16 of the 256-bit key version using 2256 steps.[2] As of 2000[update], the best published cryptanalysis on the Twofish block cipher is a truncated differential cryptanalysis of the full 16-round version. The paper claims that the probability of truncated differentials is 2−57.3 per block and that it will take roughly 251 chosen plaintexts (32 petabytes worth of data) to find a good pair of truncated differentials.[1]