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Cryptology

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by

Janna Rhodes

on 30 October 2013

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Transcript of Cryptology

Cryptology
• use of lemon juice or another weak acid (white wine, vinegar, apple juice, orange juice, or even MILK!) to weaken the paper and cause it to turn a different color when HEATED

• use of an agent to write and a reagent to reveal secret writing (such as baking soda and grape juice)
Invisible Ink
The science of
writing and reading
secret messages.

Steganography
"hidden writing"
Cryptography
"scrambled writing"
This form of steganography uses a pierced cover on top of a document that reveals only the relevant words that form the secret message.

This masked letter dates from 1777 and was written by Henry Clinton, Commander in Chief of the British forces in colonial America.
Masked Letters
A modern use of steganography is to hide data within a cover medium, such as a digital picture or audio file.

One of the simplest approaches for hiding data in an image file is called least significant bit (LSB) insertion and involves changing only a small part of the binary code for each pixel of the cover medium.
Hidden Pictures
There are two types—
substitution ciphers
and
transposition ciphers
Substitution Ciphers
Transposition Ciphers
you can use letter frequency
analysis to differentiate between the two
A method of encryption where the units of plaintext have been rearranged according to a definite system.

The ciphertext is a
permutation
of the plaintext, because it uses the same characters in a different order.
A method of encryption where units of plaintext are replaced with ciphertext according to a regular system. The units of plaintext are usually individual letters, but pairs, triplets, or other groups of consistent size can also be used.
Roman Emperor Julius Caesar allegedly used this cipher to communicate with his armies.

This cipher involves shifting the positions of two alphabets to generate the ciphertext.
Caesar Cipher
Blaise de Vigenère created this polyalphabetic (using many alphabets) cipher that utilizes a powerful new element: a KEY. To use it, one requires a Vigenère Tableau and knowledge of the key. Without the key, this is a very difficult cipher to crack!
Vigenère's Cipher
One of the major threats to the throne of Queen Elizabeth I (1533–1603) was her cousin Mary, Queen of Scots. Sir Francis Walsingham was in charge of Her Majesties spies and discovered that Mary was sending encrypted letters. He cracked her code and waited for her and her sympathizers to implicate themselves. When they did, they were arrested and executed.
The Babington Plot
Morse Code is a simple substitution cipher. Unlike many ciphers which were intended to be secret, Morse code was created to transmit accurate messages over long distances using dots and dashes to represent each letter of the plaintext. Morse designed his code with letter frequency in mind, making the most used letters in the alphabet shorter than letters used less frequently.
http://www.archives.gov/exhibits/eyewitness/flash.php
Morse Code
This cipher gets its name from the way it is encrypted, by arranging the plaintext along the imaginary posts of a rail fence.
Rail Fence Cipher
ENIGMA machines were invented by German inventor Arthur Scherbius at the end of WWI to encrypt and decrypt the ENIGMA cipher, a polyalphabetic substitution cipher. In addition to the complexity of the keywords (which changed frequently), the machine also changed electrical paths through a scrambler, providing very high security ciphertext.

The ENIGMA cipher was cracked through the hard work of many cryptoanalysts.
In particular, the research of
Alan Turing
, a Cambridge University mathematician and logician, led not only to cracking this cipher but also to the development of cryptoanalytic machines that were crucial to the Allies winning WWII.
The ENIGMA Machine
This cipher has more keys than the rail fence cipher, and is thus harder to decrypt than the rail cipher. Some keys are better than others, though!
Route Cipher
T A F S I G
The plain text:

THE EAGLE FLIES AT MIDNIGHT

is arranged in the shape of a fence:

E L I T N T
H E G E L E A M D I H
T A F S I G

and then the cipher text is read across in rows:

ELITNT HEGELEAMDIH TAFSIG
HOWEVER, THIS CIPHER IS NOT PARTICULARLY SECURE…
Even without the row boundaries shown, this cipher is fairly easy to crack, given knowledge of how many rows there are.

To make it a little more secure, one could use a key, for example 213, and arrange the cipher rows in that order:

HEGELEAMDIH ELITNT TAFSIG

Even with a key, Rail Fence Ciphers are fairly easy to crack through brute force because the encryption algorithm follows an easy and predictable pattern.

Assuming the cipher has only two rows, the odd letters in the cipher text (1, 3, 5, 7…) would be in row 1 and the even letters (2, 4, 6, 8…) would be in row 2.

With three rows, letters 1, 5, 9… are in row one, letters 2, 4, 6, 8… are in row 2, and letters 3, 7, 11… are in row 3.
WHY?
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