In preparing a presentation on cryptography for a graduate class, I was surprised by what I learned.
Cryptography has been used from ancient times through the Industrial Age to the modern day. It's been used for military, diplomatic, criminal, and commercial purposes.
In the simplest and oldest form, Greeks used strips of paper wrapped around sticks of a certain size called a scytale - rhymes with Italy.
Julius Caesar is one of the first known users of the simple letter substitution method. The modern day cousin is ROT13.
If he had anything confidential to say, he wrote it in cipher, that is, by so changing the order of the letters of the alphabet, that not a word could be made out. If anyone wishes to decipher these, and get at their meaning, he must substitute the fourth letter of the alphabet, namely D, for A, and so with the others.
—Suetonius, Life of Julius Caesar
Hiding messages (steganography) is as old as the ancients. An example would be a tattoo on a shaved head. The hair would grow back hiding the tattoo. A modern example is hiding text in the pixels of a digital image.
Charles Babbage is a name taught in every into to computer science class as a pioneer in computing machines. I never knew that he helped the English during the Crimean War by breaking cryptological codes.
Mary "Queen of Scots" was caught when one of her secret codes were broken.
The Voynich Manuscript may have been an elaborate hoax to defraud a king, who had a interest in mysteries like coded messages, out of a large amount of gold.
A mob boss used encrypted messages to give out orders to his lieutenants and was arrested when the police cracked his amateur code.
Cryptography is thousands of years old and is used all around us everyday.