With a symmetric key system (also known as secret key or private key systems), all parties have the same key. The keys can be used to encrypt and decrypt messages, and must be kept secret or the security is compromised. For the parties to get the same key, there has to be a way to securely distribute the key to each party. While this can be done, the security controls needed can make this system impractical for widespread and commercial use on an open network like the Internet.  Asymmetric key systems can solve this problem.

In an asymmetric key system (also known as a public key system), two keys are used. One key is kept secret, and therefore is referred to as the "private key." The other key is made widely available to anyone that needs it, and is referred to as the "public key."  The private and public keys are mathematically related so that information encrypted with the public key can only be decrypted by the corresponding private key.