Encryption

Encryption, also known as encoding or enciphering, is used to make data unreadable to humans unless they have the right decryption "key" to unlock the code. While encryption has been used for thousands of years, computers have allowed encryption that is virtually unbreakable.

Earlier encryption methods had a weakness: the unlocking key had to be sent to the person who was to decode encrypted files. If the key were intercepted, the file could be read. This is the failing that brought down the near-perfect Enigma coding system used by the Germans in World War 2.

Modern encryption using Public Key Encryption - for example RSA (named after its 1978 inventors, Rivest, Shamir, and Adleman) and PGP ("Pretty Good Privacy") does not need a key to be sent, and can only be broken by teams of supercomputers working for extreme periods of time, in spite of the fact that the method of encryption is public knowledge. It relies on the fact that massive prime numbers cannot be quickly factored: it would take a few billion years to crack a code that used a 1024-bit key.

Encryption is used on sensitive files on networks (e.g. password lists and secret documents) so that even if the file was stolen, it could not be read. Encryption is also used by your web browser during SSL (Secure Socket Layer) when you connect to a "Secure" site. When the padlock icon on your browser snaps shut, your communications with the secure site are encrypted so the are unreadable if they are intercepted. Some emails are encrypted to protect their privacy.

Also see -

Encryption security concerns

How Encryption Stuff Works