Note: In this section, all congruences are mod 2.
In many situations involving encryption, there is a trade-off between speed and security. If one wants a very high level of security, speed is often sacrificed, and vice versa. For example, in cable television, many bits of data are being transmitted, so speed of encryption is important. On the other hand, security is not usually as important since there is rarely an economic advantage to mounting an expensive attack on the system.
In this section, we describe a method that could be used when speed is more important than security. However, the real use is as one building block in more complex systems.