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

**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.

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

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

Hence, for symbols *x*_{0}, *x*_{1}, *x*_{2}, …, *x*_{10} if each symbol is represented by binary digits with each symbol having its own key and its own cypher text, for example

^{11}. As long as the key is not repeated, i.e., none of the binary digits chosen as keys are repeated, it is 'unbreakable'. [with 2

^{11}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) ➽