Asymmetric encryption

In asymmetric encryption a pair of keys is used. One of them is a public key and the other a private key. The keys are exchangeable in such a way that a message that has been encrypted with the public key can be decrypted with the private key of the key pair at issue and vice versa. For instance when encrypting an electronic mail message, the message is encrypted with the public key of the recipient, who decrypts the message with his own private key. As the recipient’s private key is in the possession of the recipient only, no third party can decrypt the message encrypted by the recipient’s public key.

Asymmetric encryption can also be used for ensuring the integrity of a message in such a way that the sender encrypts the message by his own private key, in which case the recipient can make sure of the sender of the message by decrypting the message using the sender’s public key (see Information security in e-mails).

One of the notable advantages of asymmetric encryption is the simplicity of key administration compared to symmetric encryption algorithms. The slowness of encryption is regarded as a weakness of the public key algorithms, in addition, the key lengths in public key encryption are kept considerably longer than in private key algorithms.

Asymmetric encryption was developed by Whitfield Diffie and Martin Hellman. However, the most popular asymmetric encryption algorithm was developed by Ron Rivest, Adi Shamir and Leonard Adleman. The algorithm was called RSA after the authors. Its strength is based on the difficulty of dividing the great numbers into their factors. Its success is based on a simple idea and easy implementation. The RSA has been patented in the United States, but the patent expired in autumn 2000. Diffie-Hellman and its further develop version ElGamal are also asymmetric encryption algorithms. Their strength is based on the problem of discrete logarithm.