What is Asymmetric Encryption (public-key encryption )?

Whitfield Diffie and Martin Hellman invented public key cryptography in 1976. For this reason it is sometime called Diffie-Hellman encryption.

This is a cryptographic system that uses two keys—a public key known to everyone and a private or secret key known only to the recipient of the message. When A wants to send a secure message to B, he uses B's public key to encrypt the message. B then uses his private key to decrypt it. An important element to the public key system is that the public and private keys are related in such a way that only the public key can be used to encrypt messages and only the corresponding private key can be used to decrypt them. Moreover, it is virtually impossible to deduce the private key if you know the public key.
Public-key systems, such as Pretty Good Privacy (PGP), are becoming popular for transmit this information via the Internet are extremely secure and relatively simple to use. The only difficulty with public-key systems is that you need to know the recipient's public key encrypt a message for him or her. What's needed, therefore, is a global registry, of public key which is one of the promises of the new LDAP technology.