Secret Key Cryptography

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.

Rivest Ciphers

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.

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