Private keys are used to encrypt or decrypt data. Part of a pair of keys used in asymmetric cryptography (e.g. public key cryptology), private and public keys are essentially non-identical large numbers that have been paired together. Either number (the private or public key) can be used to encrypt data, with the opposite number used for decryption. Public key cryptography ensures confidentiality, and public/private keys are used in Digital Signature processes, which guarantee that a message's contents were not altered in transit.