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Data Encryption Standard (DES)

DES came out of a code called Lucifer, invented by a German living in America by the name of Fiestel. This is how Lucifer worked:

• Split the original code into 64-digit blocks
• Split each block in half, so you have Right₀ and Left₀.
• Put Right₀ through an S-box (Substitution Box) that performs a complex substitution according to a look-up table.
• Add together the new Right₀ and Left₀ to make Right₁.
• Take the old Right₀ and rename it Left₁.
• Repeat the process with Right₀ and Left₀ to get Right₁ and Left₁.
• Keep repeating until you have found Right₁₆ and Left₁₆.

Right₁₆ and Left₁₆ are the coded message, and can be sent safely to the receiver. The receiver can decode the message by using the same S-boxes and performing the operation in reverse. Therefore, as with previous codes, DES is symmetric, and consists of an algorithm and a key:

One advantage of DES is that it is fairly quick to use, since the algorithm can be followed at a high speed as the calculations are not hugely complicated for a computer to work through. This is its main advantage over the likes of RSA which will be explained later.

The other advantage of DES over previous ciphers is that it is more secure, since it provides such a complex algorithm that without the key it can't be decoded. And finding the key involves searching through every possibility until the correct one is found, which is not an easy task.

However, it is possible to make a machine dedicated purely to breaking DES that can decode messages encrypted with DES in only a matter of tens of minutes.

This was shown by the first person to break the DES-encoded challenge in Simon Singh's The Code Book. The book has ten challenges to reader at the end, ranging from simple substitution cyphers that a child can break in ten minutes to highly-complex codes using DES and RSA. One man trying to solve the DES challenge rang someone he knew who operated one of the very few DES-dedicated machines, which duly spat out the answer for him a short while later.

Part of the reason for this is said to be that the US's NSA (National Security Agency) refused to allow DES (when originally made a standard in 1976) to have more than a 56-bit key. This was a large enough key to thwart any attempts by the public to decode messages, but allowed the NSA to keep a prying eye on all communications since their state-of-the-art computing facilities could just about break it. Nowadays it is possible for the public to break the code, as shown by the few who did break Simon Singh's code, so the security of DES is no longer thought to be enough for top-level security. Instead, a further version of DES, Triple DES (3DES) is used, which provides greater security.