The strength of a key is determined by its length, expressed in bits. The longer a key, the more secure messages encrypted with it will be. For example, an 8-bit key has 256 possible combinations, or ways in which to encrypt a message. Without the correct key, a recipient would have to check all 256 combinations to determine which one had been used. While this is possible with short keys, the number of combinations rises exponentially with the number of bits in the key, thus making the job extremely difficult.
Many software products on the market use 40- or 56-bit keys, while 128- bit and longer permutations are becoming common. These keys are virtually impossible to crack using brute computational force, because of the huge number of potential combinations.
There are two basic types of key cryptography: secret and public. The secret key method, the oldest and simplest, relies on both the sender and receiver possessing the same key. A sender simply encrypts and sends the message. Anyone else reading the transmission will see nothing but garbled text. The recipient decodes the message using the same key. This system works well, but becomes complex if one person wishes to communicate securely with a large number of people, as a different key has to be used for each person.
Public key cryptography is more complex, but offers a greater degree of flexibility. It works by using pairs of keys. One key is kept secret by the recipient, while the second can be distributed publicly.
A sender uses a recipient's public key to encrypt a message for transmission. Because of the unique mathematical nature of the key pair, the message can be decrypted only by using the recipient's private key. This ensures security while enabling many people to communicate with the recipient.
Some systems being developed for electronic commerce use a combination of both systems. Initial contact is established between two parties - such as a customer and a bank - using a public key system. Once the link is made, secret codes are generated and are then used to encrypt further transmissions. This ensures that valuable information remains secure.
Cryptographic experts around the world are hard at work creating ever more secure keys. Their work forms an integral part of future electronic communication and commerce.