Note: Many topics at this site are reduced versions of the text in "The Encyclopedia of Networking and Telecommunications." Search results will not be as extensive as a search of the book's CD-ROM.

A cryptographic system scrambles and secures information, encrypting it with a key so that others can only get at the information by decrypting the information with the key. However, poorly encrypted information may be cracked by wiley hackers. The most common technique is an attack in which every possible key combination is tried until the information is decrypted. Hundreds of thousands of computers may be put to work in the cracking process. Organized groups on the Internet have been successful at cracking encryptions that supposedly would take years to break. Distributed.net is such a project.

Quantum cryptography provides potentially unbreakable encryption. It is used to transmit information by taking advantage of the polarization properties of photons to store the ones and zeros of digital data. Photons have electric fields that vibrate in different directions. The direction indicates the binary value. Typically, standard encryption is used for bulk encryption of data, while quantum cryptography is used to transmit the secret key for that encryption. The technique has been used in fiber cables up to 48 kilometers.

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