Cryptography - an explanation

Cryptography allows secure communication over a general purpose insecure channel, such as the Internet.Although the mathematics behind it can be very complex, encryption itself is pretty straightforward. Cast your minds back to when you were children and you wanted to send secret messages to each other. The simplest form of encryption was the one where every letter of the alphabet was substituted for the one “n” positions following it. Here we are introduced fairly painlessly to the two most important buzzwords in the cryptography world: the “key” is the number of positions we are shifting the letters, whilst the “algorithm” is simply the idea that the encrypted letter is the one “n” places following the plain text letter. There are two ways you can beef up security on this – increase the length of the key, and devise ever more complex algorithms. Luckily, we do not have to get involved in creating our own algorithms, since there are some perfectly acceptable standards out there. The main ones currently available are DES (Data Encryption Standard), triple DES, IDEA (International Data Encryption Algorithm) and RC4 (an algorithm developed by Ron Rivest of RSA as a stream cipher with a variable key length). Whereas the original DES algorithm uses 56 bit keys, later and more powerful systems use much longer ones, forcing potential hackers to run through trillions of combinations in any attempt to find the right one by brute force. Triple DES is an enhanced version of the original DES algorithm and encrypts data three times using two different keys (providing an effective key length of 112 bits). There is also an implementation of Triple DES – known as 3DES3KEY – which encrypts data three times with three keys providing an effective key length of 168 bits, though this is much less widely deployed. IDEA is a 128 bit mechanism developed by the University of Zurich in 1992 and is a favourite of European financial institutions.

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