Symmetric Key Algorithms

Symmetric algorithms use the same shared secret key value that will both encrypt plaintext and decrypt the resulting ciphertext . Both parties share the exact same key.

Common symmetric algorithms include DES, 3DES, and AES.

Other, less common symmetric algorithms include International Data Encryption Algorithm (IDEA), Blowfish, and Carlisle Adams/Stafford Tavares (CAST).

DES

DES was originally developed in 1977 by IBM. It is a 56-bit encryption algorithm, meaning the number of possible keys "key space" is 2^56 or 72,057,594,037,927,936. Seventy-two quadrillion was a very large number in 1977 and would have taken computers hundreds of years to search the DES key space. It was considered so secure the U.S. Department of Defense adopted it as a standard and restricted its exportation.

In today's computing environment, DES is considered a weak encryption algorithm. DES is still in wide use today because it is a fast encryption algorithm that provides reasonably secure transmission of everyday (not government or top-secret) information.

3DES

As DES became more vulnerable, the Internet community required a fix. Because DES was normally based in hardware, a completely new algorithm was out of the question. As a result, 3DES was created. 3DES uses a 168-bit key. (Actually, it uses three 56-bit keys.) In essence, the 3DES algorithm encrypts and decrypts data three times with three different keys, effectively creating a 168-bit key. To this day, no one has successfully broken a 3DES key.

AES

The winner of the NIST contest was an algorithm named Rijndael, which was created by Joan Daemen and Vincent Rijmen. Rijndael (now named AES) is a variable block-length and key-length cipher. Current AES key lengths are 128, 192, or 256 bits to encrypt blocks with lengths of 128, 192, or 256 bits. AES can be implemented very efficiently on a wide range of processors and in hardware.

DES, 3DES, AES, and RSA are types of encryption algorithms.