4.3.1 Symmetric Encryption
Secret Key encryption works by taking the data to secure and passing it through a securely known encryption algorithm with a secret key, the result of the algorithm is a cipher text which is a secure representation of the original data. Diagram 4 illustrates how Secret Key encryption is used to encrypt data.
Decryption of data employs a similar process to what is shown in diagram 4, however the cipher text enters the decryption process and the original data is outputted as a result.
The main advantages of this method of encryption is that the encryption and decryption algorithms used are extremely fast and do not usually use any complex operations in there implementation. However the main problem faced with this method of encryption is for both parties to securely agree on a key which can be used to encrypt the voice sent during the session.
One such method used to allow the two parties to agree on an encryption key is with the use of an Authentication Server. Each system has a private key only known to the system and the Authentication Server. When a system wishes to communicate with another it generates a key and encrypts it with its private key and sends it to the authentication server with the address of the system it wishes to communicate with. The server then decrypts the key and re-encrypts the key using the private key of the other system and transmits the encrypted key to the other system that then decrypts the key. As a result both systems then have a secure private key in which they can communicate with each other.
However using an Authentication server can have scalability issues and if the security of the authentication server was compromised then private keys for each system would need to be reissued.
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