Symmetric vs. Asymmetric Ciphers

An important advantage of asymmetric ciphers over symmetric ciphers is that no secret channel is necessary for the exchange of the public key. The receiver needs only to be assured of the authenticity of the public key. Symmetric ciphers require a secret channel to send the secret key—generated at one side of the communication channel—to the other side.

Asymmetric ciphers also create lesser key-management problems than symmetric ciphers. Only 2n keys are needed for n entities to communicate securely with one another. In a system based on symmetric ciphers, you would need n(n ? 1)/2 secret keys. In a 5000-employee organization, for example, the companywide deployment of a symmetric crypto-based security solution would require more than 12 million keys. The deployment of an asymmetric solution would require only 10,000 keys.

A disadvantage of asymmetric ciphers over symmetric ciphers is that they tend to be about "1000 times slower." By that, I mean that it can take about 1000 times more CPU time to process an asymmetric encryption or decryption than a symmetric encryption or decryption.

Another disadvantage is that symmetric ciphers can be cracked through a "brute-force" attack, in which all possible keys are attempted until the right key is found.