Information, Computer and Network Security Terms Glossary and Dictionary

Cryptography, Data Encryption and Decryption Algorithms

There are two kinds of cryptosystems: symmetric and asymmetric. Symmetric cryptosystems use the same key (a secret key) to encrypt and decrypt a message, and asymmetric cryptosystems use one key (the public key) to encrypt a message and a different key (the private key) to decrypt it, or vice versa. The following is a list of some popular cryptography algorithms:

DES - the Digital Encryption Standard was developed by IBM and the National Security Agency (NSA) of the USA in the 50s. DES uses a key of only 56 bits, and thus it is too weak and easy to be broken with today?¡¥s technology.

IDEA - International Data Encryption Algorithm (IDEA) is a cryptosystem developed by X. Lai and J. Massey in 1991 to replace the DES standard. It is a symmetric (same key for encryption and decryption) block cypher, operating on 8 bytes at a time, just like DES, but with a key of 128 bits.

RC4 - a cypher invented by Ron Rivest, a proprietary system by RSADSI, is used in a number of commercial systems like Lotus Notes and secure Netscape.

Unix Crypt - Many Unix systems come supplied with an encryption system called crypt. This routine should never be used for encrypting anything because there exist programs on the net for producing the decrypted text and the key.

RSA - a cipher/algorithm based on the concept of a trapdoor function, which is easily calculated, but whose inverse is extremely difficult to calculate. The RSA algorithm is named after Ron Rivest, Adi Shamir and Len Adleman, who invented it in 1977. The RSA algorithm can be used for both public key encryption and digital signatures. Its security is based on the difficulty of factoring large integers.

Diffie-Hellman - Diffie-Hellman is the first published the public key cryptographic algorithm which allows two users to exchange a secret key over an insecure medium without any prior secrets. It has two system parameters p and g. They are both public and may be used by all the users in a system. Parameter p is a prime number and parameter g is an integer less than p, with the following property: for every number n between 1 and p-1 inclusive, there is a power k of g such that n = gk mod p.

PGP - a public key system for encrypting electronic mail using the RSA public key cypher. It encrypts the message using the IDEA cypher with a randomly generated key. It then encrypts the key using the recipients public key. When the recipient receives the message, PGP uses his private RSA key to decrypt the IDEA key and then uses that IDEA key to decrypt the message.

Related Terms

Diffie-Hellman, RSA, DES, RC4, PGP, Encryption, Decryption