Private Key Algorithms - Protcols

The three protocols listed here are the most common protocols in use today, and of them the RC4 algorithm is the one most people are likely to come across since it is most commonly employed inside the SSL protocols often used to provide secure Internet links.

DES

DES is an algorithm developed in the 1970s. It was made a standard by the US government, and has also been adopted by several other governments worldwide. It is widely used, especially in the financial industry.

DES is a block cipher with 64-bit block size, this means that it works on chunks of 64 bits (8 bytes) at a time and encrypts each block in turn, data not a multiple of 64 bits needs to be padded to make it so. It typically uses 56-bit keys. DES is still strong enough to keep most random hackers and individuals out, but it is easy to break with special hardware or powerful computing equipment by government, criminal organisations, or major corporations. DES is becoming weak, and should not be used in new designs.

Triple DES

A variant of DES, Triple-DES or 3DES is based on using DES three times (normally in an encrypt-decrypt-encrypt sequence with three different, unrelated keys). Triple-DES is considered to be much safer than plain DES, there is no 3rd key giving an effective key-length of 112 bits.

RC4

RC4 is a cipher designed by RSA Data Security, Inc. It used to be a trade secret, until someone posted source code for an algorithm in Usenet News, claiming it to be equivalent to RC4, analysis by cryptologists suggests that the posted algorithm really is RC4. The algorithm is very fast. Its security is debatable, but breaking it does not seem easy. Because of its speed, it is commonly used in certain applications - particularly within the open SSL standards used for secure communication between TCP/IP applications. Because of the way RC4 works it is very important that the same key never be used to encrypt two different streams of data, an attacker could then figure out the value of the RC4 key, for this reason implementations such as SSL change the value of the RC4 key regularly.

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