With secret key cryptography, a single key is used for both encryption and decryption. Because a single key is used for both functions, secret key cryptography is also called symmetric encryption.
Secret key cryptography algorithms that are in use today include :
Data Encryption Standard (DES):
DES is a block cipher employing a 56-bit key that operates on 64-bit blocks. DES uses a key of only 56 bits, and thus it is now susceptible to “brute force” attacks. Triple-DES (3DES) and DESX are the two important variants that strengthen DES.
Advanced Encryption Standard (AES )
The algorithm can use a variable block length and key length; the latest specification allowed any combination of keys lengths of 128, 192, or 256 bits and blocks of length 128, 192, or 256 bits.
International Data Encryption Algorithm (IDEA)
Secret-key cryptosystem written by Xuejia Lai and James Massey, in 1992 and patented by Ascom; a 64-bit SKC block cipher using a 128-bit key. Also available internationally.
Named for Ron Rivest, a series of SKC algorithms.
- RC1 : Designed on paper but never implemented.
- RC2 : A 64-bit block cipher using variable-sized keys designed to replace DES. It’s code has not been made public although many companies have licensed RC2 for use in their products. Described in RFC 2268.
- RC3 : Found to be breakable during development.
- RC4 : A stream cipher using variable-sized keys; it is widely used in commercial cryptography products, although it can only be exported using keys that are 40 bits or less in length.
- RC5 : A block-cipher supporting a variety of block sizes, key sizes, and number of encryption passes over the data. Described in RFC 2040.
- RC6 : An improvement over RC5, RC6 was one of the AES Round 2 algorithms.
A symmetric 64-bit block cipher invented by Bruce Schneier; optimised for 32-bit processors with large data caches, it is significantly faster than DES on a Pentium/PowerPC-class machine. Key lengths can vary from 32 to 448 bits in length. Blowfish, available freely and intended as a substitute for DES or IDEA, is in use in over 80 products.