<P> In a public key encryption system, any person can encrypt a message using the public key of the receiver, but such a message can be decrypted only with the receiver's private key . For this to work it must be computationally easy for a user to generate a public and private key - pair to be used for encryption and decryption . The strength of a public key cryptography system relies on the degree of difficulty (computational impracticality) for a properly generated private key to be determined from its corresponding public key . Security then depends only on keeping the private key private, and the public key may be published without compromising security . </P> <P> Public key cryptography systems often rely on cryptographic algorithms based on mathematical problems that currently admit no efficient solution--particularly those inherent in certain integer factorization, discrete logarithm, and elliptic curve relationships . Public key algorithms, unlike symmetric key algorithms, do not require a secure channel for the initial exchange of one (or more) secret keys between the parties . </P> <P> Because of the computational complexity of asymmetric encryption, it is usually used only for small blocks of data, typically the transfer of a symmetric encryption key (e.g. a session key). This symmetric key is then used to encrypt the rest of the potentially long message sequence . The symmetric encryption / decryption is based on simpler algorithms and is much faster . </P> <P> In a public key signature system, a person can combine a message with a private key to create a short digital signature on the message . Anyone with the corresponding public key can combine a message, a putative digital signature on it, and the known public key to verify whether the signature was valid--made by the owner of the corresponding private key . Changing the message, even replacing a single letter, will cause verification to fail: in a secure signature system, it is computationally infeasible for anyone who does not know the private key to deduce it from the public key or from any number of signatures, or to find a valid signature on any message for which a signature has not hitherto been seen . Thus the authenticity of a message can be demonstrated by the signature, provided the owner of the private key keeps the private key secret . </P>

Who was involved in developing the first public key algorithm