Asymmetric cryptography is a synonym for public key cryptography. Asymmetric cryptography provides users with both a public key and a private key. The public key and private key are mathematically related but it is very difficult or impossible for the private key to be discovered using the public key. The public key can be given to anyone and the private key must be kept secret. There are two main uses for this type of a key system. These are.
- To allow anyone to pass a secret message to one person who holds the private key. This method provides confidentiality.
- To allow someone to send a message that they can prove they have sent. This method provides sender authentication.
This system allows users to communicate securly without having previously shared a secret or key.
To pass a secret message to one person, the message is encrypted with the public key of that person. The message then can only be decrypted with the person's private key. In this case the message can only be decrypted by the owner of the private key.
To allow someone to send a message and prove they sent it, the message is encrypted with the private key of the person sending the message. Then anyone can decrypt and read the message with the public key. If the public key can be used to successfully decrypt the message, it is proof that the message was really sent by the person who claimed to send it. This method can be used so the author of the message cannot deny having created or sent the message. Normally the hash or CRC value of the message is the only part encrypted to verify the sender of the message. This process is commonly known as a digital signature.
Asymmetric cryptography is usually slower when encrypting and decrypting data than symmetric cryptography.