Types of Symmetric Encryption Algorithms
A symmetric encryption algorithm is a mathematical formula that converts plain text into an unintelligible, encrypted form, known as cipher text. The variable, or encryption key, used to drive a symmetric encryption algorithm is derived from a passphrase supplied when the data is encrypted and a single, shared key is used to encrypt and decrypt data. Several different types of symmetric encryption algorithm exist and their strength depends, largely, on the length, in bits (0s and 1s), of their encryption key.
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DES
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The Data Encryption Standard (DES) was the first encryption standard recommended by the National Institute of Standards and Technology (NIST), back in 1977, but has been subject to many attacks in the interim and, nowadays, is only permitted for legacy systems. A DES encryption key consists of 64 bits, but only 56 bits are used directly by the DES algorithm; the remaining 8 bits in the key may be used for error detection.
Blowfish
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Blowfish is a public domain symmetric encryption algorithm -- that is, it is unlicensed and available to everyone, free of charge -- first introduced by one of the world's leading cryptographers, Bruce Schneier, in 1993. Blowfish uses a variable-length encryption key, ranging for 32 bits to 448 bits, with a default of 128 bits. In its simplest form, plain text is divided into 64-bit blocks and fed into the algorithm to create blocks of cipher text.
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3DES
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Triple DES (3DES) is an enhancement of single DES that applies the DES encryption method to the same data three times to increase the encryption level. Triple DES increases the length of the encryption key to 192 bits, but is slower than other blocker cipher encryption methods. Nevertheless, 3DES replaced DES as the symmetric encryption algorithm of choice in 1999, according to the Federal Information Processing Standards (FIPS).
AES
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The Advanced Encryption Standard (AES), which is actually an implementation of a symmetric encryption algorithm known as a Rjindael, is the latest standard recommended by the NIST. AES uses a encryption key varying in length from 128 bits to 256 bits and encrypts data in blocks of 128 bits. The AES algorithm is applied to data 10, 12, or 14 times -- known as "rounds" -- making it highly secure. In fact, only a so-called brute force attack, in which an attacker tests all the possible combinations of the encryption key, has proved effective against AES. Nevertheless, AES is fast, flexible and can be implemented on a variety of different platforms.
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