Overview

This is a very simple proof of concept tool to demonstrate OTP (One Time Pad) encryption at a binary level. There are three lines of output for each plain text character input - PLT (PLain Text), KEY (the OTP key value), and XOR (the encrypted version).

The first two lines are XOR'd to form the third line. Decryption occurs simply by XOR'ing the second and third line, which should give you the first line. And for the sake of completeness, you can XOR the first and third line to get the second line.

In this implementation, if the key argument is shorter than the plain text argument, the key is reused. In a real OTP implementation, one would NEVER reuse any portion of the key.

As is the case with all encryption code, unless you are an expert in the specific algorithm you are implementing, you should not be writing your own code. As I am not an expert, I would strongly advise against using this code for anything other than demonstration / POC purposes.

XOR Truth Table

A B  | O
--------
0 0  | 0
0 1  | 1
1 0  | 1
1 1  | 0

Build Instructions:

gcc -Wall -Wextra simple_otp.c -o simple_otp

Usage Instructions:

./simple_otp "Hello World" "secret"

Example Output:

PLT: H  01001000
KEY: s  01110011
XOR:    00111011

[ ... ]

PLT: d  01100100
KEY: e  01100101
XOR:    00000001