Since most encryption algorithms are published and well known, the security of the data being processed is dependent upon the secrecy of the key. The destruction or loss of the key is equivalent to the loss or destruction of the data itself. Encryption techniques can be divided into two general categories, symmetric or private key techniques and asymmetric or public key techniques. In private key encryption, the receiver of a message uses the same key to decrypt the message as the sender used to encrypt the message. Public key encryption provides both the sender and receiver with two keys, one private and one public.
Private keys are the secret of their users, while public keys are openly available via a directory.
When public key encryption is used, the sender encrypts the message in the public key of the intended receiver. Upon reception, the message is decrypted with the receiver's private key. Public key encryption technology simplifies the processes of key distribution and implementation of authentication functions. For these reasons, public key encryption technology is specified as part of the OSI X.500 Directory Service. However, no standards have been adopted for the specific public key encryption algorithm that will be employed.