Encryption systems include either shared key, public key, or secure key exchange. With shared key encryption, all parties get issued a key that unlocks the data. The sender provides the key to a shared symmetrical encryption algorithm used to encode the data before it gets placed in the packet headed for the remote site. To decode the data in the packet, the remote site provides the key to same encryption algorithm. Public key encryption occurs when one party has a private unlocking key and makes a public locking key.
Any sender can use the public key to encrypt the data.
The receiver, in turn, uses its designated private key to decrypt the data. Often used with digital certificates, secure key exchange requires that both parties first authenticate themselves during a session to distribute the encryption key. The parties can use the resulting key to encrypt and decrypt any forthcoming data. A good security system should allow itself to be controlled by a human authority. For example, an authentication system requires someone to verify identifies, such as a password file on a Windows NT domain controller.