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Chapter 7:
Cell Phone Medical Image Encryption Based on a Method of 3D Spirals
The word cryptography comes from two Greek words “Krypto” (secret) and “ϒrafh” (writing); putting these words together, cryptography means simply the art of secret writing enhancement.1 Cryptography was born almost 4000 years ago, in a town called Menet Khufu bordering the thin ribbon of the Nile, where a master scribe sketched out the hieroglyphs that told the story of the nobleman Khnumhotep II. This master scribe simply replaced some more ordinary hieroglyphic symbols with some unusual ones, with the intention of imparting dignity and authority to his lord’s life, not to make the hieroglyphs difficult to read. The first military cryptography system was established by the Spartans, the most warlike of the Greeks. This system consisted of a skytale, which was basically a staff made of wood, and a piece of leather; the piece of leather was wrapped tightly around the staff, then a secret message was written down the leather. Once the secret message was written, the leather was unwrapped from the staff and worn as a belt. The disconnected letters made no sense to an individual unless the leather was rewrapped around a staff of the same thickness as the first staff and then read.2 This Spartan cryptography system was used in 405 B.C. by Lysander, a Spartan general, and eventually aided him in learning that the Persians were indeed scheming against him. This led to Lysander attacking and ultimately winning against the Persians, saving himself and the Greek empire. Fast forward to a little over a millennium later; Thomas Jefferson (father of American cryptography) with the potential help of Robert Patterson (a mathematician of the University of Pennsylvania) invented the wheel cipher, where cipher refers to an encryption scheme. This device consisted of multiple thin wooden wheels of the same thickness containing the 26 letters of the alphabet that are randomly ordered but equally spaced on each of the rims of the wheels. The wooden wheels were then numbered, and a hole was placed in the center of each of the wheels. Then each wheel was placed in a specific order on an iron spindle and secured with a nut and screw. A user would then turn the wooden wheels until the message was spelled out across one line; since each wheel has 26 possible characters, the user would have 25 additional messages (each message is on one line) created by the wooden wheels that would be jumbled and without order or meaning. The user would then choose one of the 25 possible jumbled messages and send this to another person with whom they would like to share their secret message. The correspondent would have a similar cylinder and would arrange the wheels to create the same jumbled message on one line of the wheel cipher. The correspondent would then examine the other 25 lines until he or she finds the line with the secret message, as the other lines would contain jumble and have no meaning. Note that by changing the order of the wooden wheels, a variety of different ciphers could be produced for different correspondents. Jefferson proposed that this wheel cipher have 36 wooden wheels, which would mean that a wooden cipher could form 36! different ciphers for different correspondents.
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