Encryption methods

Encryption methods aim at ensuring the confidentiality, integrity and non-repudiation of information. Regardless of the purpose to which the encryption is used for, the goal should be that breaking the encryption within a reasonable time and with reasonable resources is not possible. The definition of a reasonable time and reasonable resources depends in each case on the importance of the information to be encrypted.

When estimating the applicability of an encryption method, the starting point is an encryption mechanism the breaking of which is not reasonable from the computing point of view. Such methods the breaking of which by present computing resources available to an attacker is not possible are often called strong encryption methods. The computing capacity of modern computers easily enables the use of strong encryption methods in data protection, so there is no obstacle to the use of such methods.

It is to be remembered that certain countries further restrict the level of encryption by law. In the Finnish legislation there are no restrictions to the level of encryption to be used.

The starting point for the development of encryption methods is that the security of the method is based on encryption keys used and that the secrecy/publicity of the method itself does not affect the security of the mechanism. In successfully performed methods of encryption the decryption is possible only by going through the whole key space of the encryption method and by trying all possible keys for decryption.

Generally speaking it can be said that the longer the encryption key the stronger it is. Let’s presume that one computer is capable of going through one million encryption keys per second. If a million of such computers are coupled together to break an encryption key of 40 bits, it takes a little more than one second ((240 / (1 x 1012) to go through all encryption keys. Similarly, the time with a 128 bit key is about 11 trillion (11 x 1018 ) years. The great difference between the above mentioned key lengths is based on the fact that each bit added to the key length doubles the number of possible keys.

The encryption methods consists of two main categories, stream and block cipher encryption. Stream cipher encryption means that a clear text is encrypted character by character. Stream cipher encryption methods are mainly used in on-line applications, which require great speed. In block cipher encryption the clear text is encrypted block by block. Block cipher encryption is used in the most common symmetric and asymmetric encryption algorithms.