A mathematical entity used in cryptography for the encryption of messages and for signing messages with digital signatures.

In secret key (or symmetric key) cryptography, both the sender and the recipient use the same key for encrypting and decrypting messages. Public key cryptography uses a key pair that consists of the private and public keys of the sender.

The degree of security of a key depends on the type of mathematical algorithm used with the cryptosystem and the length of the key. Most cryptography algorithms make use of transformations using prime numbers and congruency.

Key lengths range from 40 bits for the RC2 and RC4 cryptography algorithms to 512 bits for RSA public key systems.

You obtain keys from certificate authorities (CAs) by submitting a key request file, such as one generated by the Key Manager component of Internet Information Services (IIS).