A secret key is the piece of information or parameter that is used to encrypt and decrypt messages in a symmetric, or secret-key, encryption.
In assymetric encryption,
two separate keys are used. One is a public key and the other is a secret key.
A secret key may also be known as a private key.
When using symmetric encryption, only one key is used for encryption and decryption. However, in asymmetric cryptography there is both a private key and a public key involved in the encryption and decryption processes. The secret key can be kept by one person or exchanged with someone else when sending encrypted messages. If only one key is available for both encryption and decryption, both the sender and receiver of a message have to have a copy of the secret key to be able to read the message.
The most difficult aspect of this type of encryption is how to distribute the key to a second party without affecting security.
Secret key cryptography systems are often classified to be either stream ciphers or block ciphers. Stream ciphers work on a single bit at a time and also use some kind of feedback mechanism so that the key changes regularly. A block cipher, on the other hand, encrypts one data block at a time by using precisely the same key on every block.
The most accepted secret key cryptography scheme is Data Encryption Standard (DES) cryptography. Other cryptography systems used for secret-key encryption include the Advanced Encryption Standard (AES) and CAST-128/256.