Encryption

Encryption is the process of making data secure by making extremely difficult for any one but the intended user to understand. There are many ways to do this.

The history of encryption goes back a long way, to when certain Greeks had reasons to be more private with some of their written matter! Their system involved swapping letters for their alphabetical successor, a goes to b, b to c, z to a. While this fooled people for a while, it became obvious that this system could be read easily if you recognised it. Next they swapped letters with say the seventh letter afterwards. This was harder to read, but with only 26 possible possibilities, really there was only temporary security (this is used in ROT13). Systems were devised that took the message and put in a whole lot of other words, with the receiver knowing to read say every 10th word, or any word with a capital. This what’s called an obscurity method, and is not true cryptography.

In the 2nd world war, some more advanced crypto systems were used on both sides. The best known was the ENIGMA machine. This system was the most advanced crypto system devised up to that time, and Germany was so sure it could not be broken that they used it for all there communications throughout the war. The major weakness of the Enigma was that it could not code a character as its self. It could still however render many millions of permutations. Unbeknown to the Germans, the Polish underground broke the code in 1940-41 and for the rest of the war the Allies were able to cryptanalyse the code. The Enigma was a ‘rotor’ code, using a set of 5 rotors (only 3 were used, 4 for U-boats).

This system was possibly the first example of a crypto system were all the security was in the key. In more conventional systems, it was important to protect the method of encryption, as reversal could give you the ‘plain text’ . The Allies captured many Enigma machines, but they were no use for decoding, as all the security information was stored in the key. This meant that the big heavy machines were not in them selves a security issue. Only the daily rotor settings mattered. These 3 or 4 letter codes gave the positions for the rotors. A number also told the operator which rotors to put in the machine, and provided a few more settings for added complexity. (A machine could be setup in a minute, then a message was typed, with the encrypted text showing on a small display, Essentially it was a simple computer! )

The Enigma caused a lot of interest in crypto, and as computers developed in the 50’s, one of their first applications was making and breaking codes. A new age of data-privacy has become available with academic unclassified research into systems that can provide a typical citizen with security enough to stall a major government. Adopting the Enigma approach of key-based security was an important step. Another was the Public key style of systems. These systems use what are called ‘One way’ algorithms.

The idea of a one way system is this. Given ‘plain text’ a Key and a one-way algorithm you can produce ‘crypto text’. Given that crypto text and the same algorithm and Key, you can not get the plain text. To obtain the original text you need a different key (and the same algorithm). This gets around the problem of telling any one your key. You make publicly available your Public key, but this key is only any good for encrypting data. Once encrypted, the plain text is only available on application of the ‘Private key” with the algorithm. This separates crypto systems into single and dual key systems. Single key systems are more secure, but distribution of a key requires a secure channel. If a secure channel is available, then these can be called shared secret systems.

Gatekeeper uses a shared secret (the key) which is part of the program. For anything to communicate with Gatekeeper, it must know this secret, and know how to use it, to be able to negotiate a connection.