Rome’s legendary dictator Julius Caesar (100BC-44BC) had many enemies. To protect himself and his plans, Caesar started using a cipher. By coding each of his personal letters with a simple system: With help of the alphabet, he would write a letter and then shift it 3 times to the right.
The letter “B” would become an “E” and so forth. Although quite simple, the Caesar Cipher did its trick and according to all sources it was never cracked. Caesar was perhaps only the most famous user, but neither the first nor the last. Some variation of the cipher was used up to 1915 by the Russians during the First World War. However, the code proved much too simple for the enemies. It was cracked almost instantly by the German and Austrian cryptanalysts. Mathematics, logic and code cracking had come a long way since Roman times.
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Photo Credits / Sources:
By Matt_Crypto (http://en.wikipedia.org/wiki/File:Caesar3.png) [Public domain], via Wikimedia Commons