the use of any code system. The sender and receiver both agree to encode and decode a message using a specific key--be it a substitution algorithm or some other more complex approach--and this provides the secrecy. Without the key to the code, it is difficult and time-consuming to break well-encoded messages. At least this was the case before machines became commonplace. The Germans used the Enigma machine during World War II to encode their messages, and the encoding key was changed on a regular basis. Although the Allies procured working Enigma machines, they still needed to know which key was used to set the machines (Levy 11).
Computers changed the cryptography landscape, however. Where it once required hundreds of people working thousands of hours to break codes, computers made it possible to perform millions of calculations quickly. It was increasingly possible to break most encryption schemes through the use of computers.
When two people want to keep messages they are exchanging secret, they use a code. In order to decode the message, each participant needs to have a key to successfully decrypt the code. When both keys are secret, the code is said to be symmetric, or private; symmetric codes require that both the sender and receiver have the secret key, and security problems come into play as the participants seek to keep the key secret. Public key encryption differs fr
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