A Basic Cryptography System

A basic cryptography system consists of a message X ☐ and a key K ⬤ such that the key covers the message in modulo ⊕.

Fig 1 Illustration of components of Alice
These three constitutes to form the information source equivalent also called Alice.

Now, for Bob to receive information from Alice, Bob must have the key to decrypt the information.

Fig 2 Bob receives information from Alice

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But a 3rd person Eve (eavesdrop ۞) may try to get information from Alice

Fig 3 Eve try to evesdrop message sent by Alice to Bob

However a cypher text is placed to prevent Eve from getting the information.

Fig 4 Message sent by Alice to Bob with cyphertext

Hence, for symbols x0, x1, x2, …, x10 if each symbol is represented by binary digits with each symbol having its own key and its own cypher text, for example

X: 1 0 1 1 0 1 1 1 0 1 0, K: 0 1 1 0 1 0 0 1 1 0 1 C sub y: 1 1 0 1 1 1 1 0 1 1 1
In this example of eleven binary digits used, the possible number (ways) of keys is 211. As long as the key is not repeated, i.e., none of the binary digits chosen as keys are repeated, it is 'unbreakable'. [with 211 keys breakability will depend on how redundant X is]

This continuously chosen keys so that none of the binary digits repeat is called a 'one-time pad'.

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Error rate (p:3) ➽

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