acker (http://www.eff.org/descracker/). This $220,000 device can break a DES key in an average of 4.5 days." (Dr. Dobb's Journal: The Current State of DES)
Triple-DES is only a third as fast as DES, but uses three keys to effectively triple the key length to 168 bits, making the algorithm "billions of times more secure [than DES] if used properly." (Tropical Software: Triple DES Encryption [Triple DES])
Diffie-Hellman is an encryption algorithm that employs the asymmetric key model.
"In 1976, Diffie and Hellman started an explosion of open research in cryptology when they first introduced the notion of public-key cryptography, which allows for new electronic means to handle key distribution in conventional cryptographic systems and for digital signatures in electronic messages." (Cylink Resource Library: Alternatives to RSA: Using Diffie-Hellman with DSS)
"The Stanford patent on the Diffie-Hellman technique... expired in 1997 and [the technique] is now in the public domain." (Cylink Resource Library: Alternatives to RSA: Using Diffie-Hellman with DSS)
GOST is the U.S.S.R. 28147-89 standard protection algorithm, analogous to the U.S.'s DES. "The algorithms are similar in that both operate on 64-bit blocks by successively modifying half of the bits with a function of the other half." (GOST encryption algorithm: Russian analogue to US Standard?)
IDEA is a block cipher used in PGP. "IDEA, unlike the other block cipher algorithms discussed in this section, is patented by the Swiss firm of Ascom. They have, however, been generous in allowing, with permission, free noncommercial use of their algorithm, with the result that IDEA is best known as the block cipher algorithm used within the popular encryption program PGP." (IDEA (International Data Encryption Algorithm)
See "Data Encryption Standard (DES) and Triple-DES (3DES)"
"Twofish is a block cipher by Counterpane Labs. It was one of the five Advanced Encryption Standard (AES) finalists. Twofish is unpatented, and the source code is uncopyrighted and license-free; it is free for all uses." (Counterpane Internet Security: Twofish: A New Block Cipher) It operates under the symmetric key model.
RSA is a family of algorithms that employ the asymmetric key model. There are actually multiple incarnations of this algorithm; RC5 is one of the most common in use, and RC6 was a finalist algorithm for AES. Searching for how RSA works often yields a host of pages about how it works mathematically, because the U.S. patent on the RSA algorithm expired on September 21, 2000. (RSA Security, Inc. actually began offering the algorithm to the public before the 17-year-old patent expired.)