Introduction to Cryptography and Steganography

by Amir Sadeghian Posted on | Information Security

Cryptography is an interesting art. Bear with me and you will see. In this post, I will tell you a brief history of Cryptography and Steganography. The next post will be more technical.

A long time ago ancient dynasties rely on different methods of communication in their region. They always were interested in new methods to hide their message from potential enemies. The interest of enemies in those important messages encouraged dynasties to develop new methods to secure their messages using codes and ciphers. Like everywhere else our story has two sides. One the other side enemy forces had some workers who were responsible for breaking the codes and revealing the secret message. The battle between inventors of new coding methodologies and code breakers always continued and this cause many more new methods of coding being invented. In the new era, the act of hiding the message in the form of code is called encryption. The reverse method to retrieve the secret from the encrypted message is called decryption. The art of changing plain content to a secret message that is not understandable by others is called Cryptography. In cryptography, only entities that have the key for that secret are able to decrypt the secret message(Which is true only in the best scenario).

The earliest method of secret messaging is related to 519–465 BC, when there was a war between Greece and Persian(Iran). According to Herodotus, the art of secret messaging saved Greece from being conquered by Xerxes, King of Kings, leader of Persians. After Xerxes build his new kingdom capital at Persepolis, gifts arrived from all over the empire and neighboring countries except Athens and Sparta. This made Xerxes say “We shall extend the Persian territory as far as God’s heaven reaches. The sun will then shine on no land beyond our borders“. Then he spent 5 years secretly preparing the greatest army in history to do a surprise attack. Long story short, one Greek betrayer who was not welcomed by his homeland was working in the Persian army. He still had some feelings and loyalty to his country, therefore he decided to send a message to them and inform them about this surprise attack. He has to hide the message to avoid discovery by Xerxes people. Therefore he scraped his message on a wooden folding tablet and then he covered the message with wax. This avoids guards on the way to find out about the secret message. The message delivered safety to Greeks. Greeks prepared themself for the war and they won the war against Persians.

There was another method used in the same era. In this method head of a person as messenger shaved and then the message was written on his scalp, then they will wait for his hair to regrow. 

The art of hiding the existence of the message known as Steganography. Previously mentioned stories were good examples of Steganography In cryptography, the message is viewable by the public but the content of it is not understandable to them. However, in Steganography the message itself is hidden from view.

Ancient Chinese used to write their secret messages on silk and make them like a ball, then cover them in wax. A messenger has to swallow the waxed ball to hide the message. 

Part of Steganography is writing messages using invisible inks. In the 16th century, Giovanni Battista Della Porta an Italian scholar explained his finding of writing a secret message on boiled eggs. He made an ink using a mixture of vinegar and alum. Then he used the ink to write on the shell of the egg. The ink penetrates through the shell and leaves the message on the hardened albumen of the egg. The message does not appear on the shell and only will appear after the shell is removed.

Even though Cryptography and Steganography are two different methodologies, they can be used together to increase the secrecy of the message. For instance, during World War II, German spies in America used photographic technics to shrink a page of text to a size less than a millimeter. Then they used this dot at the end of their first sentence in their letters. After a while, the FBI found out about the microdots, and then they were able to read the content of them and intercept the message of spies to Germany. Then Spies combined the art of cryptography with Steganography to scramble their text before converting it to microdot. Afterward, the content of microdots was not understandable to Americans, however, they were able to block the communication.

In the next post, I will explain the basics of cryptography and will give a few examples of primitives methods of encryption. Please start following my blog using G+, FB, Twitter. I promise you will not regret it and we will cover more about new techniques of cryptography.

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