In cryptography, a revolutionary new method of encryption that does not require the message’s receiver to have received the decoding key in a separate transmission. The need to send the key, which is required to decode the message, is the chief vulnerability of previous encryption techniques.
In public-key cryptography, there are two keys: a public one and a private one. The public key is used for encryption, and the private key is used for decryption. If John wants to receive a private message from Alice, John sends his public key to Alice; Alice then uses the key to encrypt the message. Alice sends the message to John. Anyone trying to intercept the message en route would find that it is mere gibberish. When John receives the message, he uses his private key to decode it. Because John never sends his private key anywhere or gives it to anyone, he can be certain that the message is secure. Public key cryptography places into the hands of individuals a level of security that was formerly available only to the top levels of government security agencies.