The process of rendering a message (or data) unusable to all but the intended recipients, who have the ability to decrypt it. Cryptography is the science of creating workable procedures for encrypting and decrypting messages.
The goal is to ensure that a message intercepted by a distrusted user cannot be decrypted in a feasible amount of time.
Although there are many different approaches to encryption, the two most common are
For example, if user A wanted to send an encrypted message to user B, it would typically work like this:
Graphic E-3. The public key encryption method.
The preceding approach outlines the steps used for encrypting and decrypting the actual message being transmitted during a secure communication session. A different approach, called a digital signature, is used to confirm the authenticity of the sender and the integrity of the message. Digital signatures are encrypted in a reverse fashion to the message itself. Specifically, if user A wants to send his digital signature to user B, then