Encryption algorithms come in two basic flavors: symmetric and asymmetric.

I’ve already discussed symmetric encryption which is basically defined by the use of one and the same key for encryption and decryption. Such symmetric encryption algorithms include AES, DES and Triple-DES.

The basics of symmetric encryption go something like this: supply plaintext and an encryption key to an encryption method, let the encryption method process the two components of information together, receive the unreadable output and then extract the meaning from the unreadable output by using the same encryption key.

With asymmetric encryption the process involves not one but two keys: one key for encryption and a second key for decryption.

It is possible for the two keys to be interchangeble but it is not necessary. For example, key E encrypts a message and then key D decrypts the message. The reverse would also be true – if they are interchangeable – so you could have the flip scenario where key D encrypts a message and key E decrypts the message. Although this is possible it is not usually the norm.

Asymmetric Encryption is also known as Public Key Cryptography where users create a matching key pair with one key as the public key and another key as the private key.

In an asymmetric key pair, the key that is used as the private key for encryption would be useless as the key for decryption. Likewise, the public key used for decryption would be useless for the encryption.

This is an effective means of secure communication since, if you receive an encrypted message from someone you know, and you use their public key to decrypt the message then you can reasonably be assured that the message came from the sender since only their private key could have encrypted the message decrypted by their public key which you hold.

The most popular asymmetric encryption algorithm is known as RSA which was developed by Rivest, Shamir and Adleman. Another asymmetric algorithm that I have discussed in another post is the Diffie-Hellman algorithm.
 
The success of asymmetric encryption is dependent on the reliability of trusted public keys. A Public Key Infrastructure, which is a key management system, is necessary as a component to the successful use of asymmetric encryption. Another approach, Pretty Good Privacy (PGP), ensures the authenticity of key pairs. Either method can be used to establish the reliability of public keys for use with asymmetric encryption.