public key cryptography

An encryption method that uses a two-part key: a public key and a private key. To send an encrypted message to someone, you use the recipient's public key, which can be sent to you via regular e-mail or made available on any public Web site or venue. To decrypt the message, the recipient uses the private key, which he or she keeps secret. Contrast with "secret key cryptography," which uses the same key to encrypt and decrypt. See cryptography.

Digital Signatures Reverse the Procedure
To create a digital signature that ensures the integrity of a message, document or other file, the keys are used in reverse. The private key is used to sign the file (encrypt the digest), and the public key is used to verify it (decrypt the digest).

Public Key Methods Used in Combination

The private key of the sender is used to sign the message, and the public key of the recipient is used to encrypt the signature and the message. For more details, see digital signature.