Asymmetric Algorithms
Asymmetric encryption algorithms, also known as public key algorithms, use separate keysone for encryption and another for decryption. The encryption key is called the public key and can be made public. Only the private key that is used for decryption needs to be kept secret. Although the public and private keys are mathematically related, it is not feasible to derive one from the other. Anyone with a recipient's public key can encrypt a message, but the message can only be decrypted with a private key that only the recipient knows. Therefore, a secure communication channel to transmit the secret key is no longer required, as it is in the case of symmetric algorithms.
The initiator and responder communicate securely using public key encryption as follows:
| 1. | Initiator and responder agree on a public key algorithm. |
| 2. | Responder sends initiator his public key and initiator sends responder her public key. |
| 3. | |
| 4. | Responder receives the message and decrypts initiator's message using his private key. |
Remember that public key encryption is rarely used to encrypt messages because it is much slower than symmetric encryption. Public key encryption is used, however, to solve the problem of key distribution for symmetric key algorithms, which is, in turn, used to encrypt actual messages. Therefore, public key encryption is not meant to replace symmetric encryption, but can supplement it and make it more secure.