• DES (and its variations)
• IDEA
• SAFER
• RC2
• RC4
• RC5
• FEAL
• SKIPJACK
• BLOWFISH
• SEAL

DES (and its variations)

DES stands for Data Encryption Standard and it is an iterative block cipher developed at IBM and defined by the U.S. government as an official standard in 1977. DES block size is 64 bit long, and it use a 56 bit key (16 rounds) during encryption. It has been estimated that a specialized computer costing 1 millions dollars requires 3.5 hours to perform an exhaustive search (brute force attack). However I can't assure this assertion at all, as CPU speed-rates are becoming more and more high (and less expensive in the same time). In fact keys less than 128 bit are considered insecure by now. Tomorrow? Even 128 bit keys might be insecure...

Triple-DES is a variation of DES: it encrypt the plaintext 3 times. Triple-DES may be: DES-EEE3 (encrypt-encrypt-encrypt), DES-EDE3 (encrypt-decrypt-encrypt), DES-EEE2 (encrypt-encrypt-encrypt). DES-EEE3 uses 3 different secret keys during encryption. DES-EDE3 uses 3 different keys again, but in the sequence encrypt-decrypt-encrypt. DES-EDE2 is the same of previous format but it uses 2 different keys. G-DES and DESX are other variant of DES.

IDEA

IDEA stands for International Data Encryption Algorithm. It is a 64 bit iterative block cipher with 128 bit key (8 rounds).It is considered to be immune from cryptoanalysis attacks such as differential cryptoanalysis and linear cryptoanalysis. IDEA is generally considered secure. What about brute force attacks? Well, a 128 bit key means that any one of the 2^128 possible combinations may be a possible key. So...just try to compute 2^128. In other words a 1 MIPS computer should work years, and you couldn't see the solution...Don't be confused with public key systems. In fact, look this table showing the estimated equivalencies between brute force key searches and factoring of public keys:

SAFER

SAFER stands for Secure And Fast Encryption Routine. It is a block cipher developed by Massey in 1993 for Cylink Corporation. It use a 64 bit block size.

RC2

RC2 stands for Ron Code or Rivest's Cipher. It is a block cipher (64 bit) developed by Rivest for RSA Data Security. It uses a variable key size. In fact it can be made more or less secure than DES by varying the key size. It is about 2 or 3 time faster than DES.

RC4

RC4 is a stream cipher developed by Rivest for RSA Data Security. It is a variable key length algorithm.

RC5

RC5 is a block cipher developed by Rivest for RSA Data Security. It is a parameterized algorithm, in fact it has a variable block size, a variable key size, and a variable number of rounds. The block size may be 32, 64 or 128 bits long. The key size may be from 0 up to 2048 bits. The number of rounds may be from 0 to 255.

FEAL

FEAL stands for Fast Encipherment Algorithm. It is a block cipher developed by Shimizu and Miyaguchi. As several wake attacks were announced it should be considered insecure.

SKIPJACK

SKIPJACK is the algorithm contained in the CLIPPER chip. It was designed by NSA (National Secure Agency). It uses 64 bit block size and a 80 bit key. It can't be implemented in software, but only in hardware by government-authorized manufacturers.

BLOWFISH

BLOWFISH is a iterative block cipher developed by Schneier.

SEAL

SEAL stands for Software-optimized Encryption Algorithm. It is a stream cipher developed by Rogaway and Coppersmith in 1993.