Symmetrical encryption is a method in which the keys used to encrypt and decrypt data are identical. For symmetrical encryption the sender and the recipient must first agree on a key which they will use, or the encryption parameters and method which will allow both the recipient and the sender to create identical keys. If the same key is used for a longer period the risk arises that after some time another person may decode the information protected by the encryption using sufficiently powerful computing technology and knowledge of the encryption method. The advantage of symmetrical cryptography is that it requires less computing power for both encryption and decryption, which means higher speed of encrypting and decrypting, and a reduced delay caused by the encryption and decryption on cryptographic devices. This leads to a high through-put of the communication link secured by the cryptographic means.