Due to the insecure nature of Internet communication, encryption techniques are used to protect data confidentiality. There are two major forms of encryption techniques, one is Symmetric Key Crypto-System, the other is Public Key Crypto-System. Let's look at Symmetric Key Crypto System first.
In a
Symmetric Key Crypto-System, users, say Thomas and Peter, hold shared key K.
When Thomas wants to send a message to Peter, Thomas encrypts the message with
K, and sends the encrypted message. After Peter received
the encrypted message from the Internet, he uses K to decrypt
it, and gets back the original message.
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