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# Cryptography

Math ISU on Cryptography by Sarah Diaz and Trisha Asuncion
by

## Sarah Diaz

on 20 January 2013

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#### Transcript of Cryptography

by Sarah Diaz and Trisha Asuncion Cryptography Cryptography is a method of securing
information for privacy purposes. History What is cryptography? The word cryptography comes from the Greek words kryptos (hidden) and graphia (writing)
Cryptology is the branch of mathematics and science that deals with cryptography
The first method of cryptography was used thousands of years ago in the form of hieroglyphics Claude Shannon Claude Shannon is considered the father of cryptology
He was the man who worked with communication security in World War II
He published a book in 1949 called "Communication Theory of Secrecy Systems"
The book was about his communication security systems, which incorporated mathematics Portrait of Claude Shannon Encryption Encryption is the function of translating plain text into a coded file
It involves taking regular plaintext/cleartext (unprotected information) into an unrecognizable format called ciphertext
There are three different types of encryption: symmetric key encryption, substitution cipher, and transposition cipher Symmetric Key Encryption The oldest form of encryption
It has been used for over three thousand years to safeguard communications
It uses a shared secret key to encrypt and decrypt data Substitution Cipher Substitution cipher is where letters are represented by other letters
By knowing the order of the cipher alphabet, you are able to decipher the message
Simple substitution cipher - a cipher that operates on single letters
Polygraphic - a cipher that operates on a group of letters Transposition Cipher Decryption Decryption is the method of breaking into an encryption to be able to access the original plain text
To decipher a message, you need a key
The key is an algorithm (a set of rules to be followed in calculations or other problem-solving operations)
Decryption is not an easy task to perform Transposition ciphers are rarely used
The letters of the plaintext are shifted about to form the cryptogram
There are systems where even words are shifted instead of single letters
There are several branches of this type of cipher: morse code, route ciphers, and columnar ciphers Caesar Cipher The Caesar cipher was invented by Julius Caesar
This method is also called "shift by three"
For each letter, shift by three, and use that letter instead
For example, in place of the letter A, you would use D instead Caesar Cipher Alphabet Public Key Cryptography The following video shows the process of trying to decode a message to get the original key. Hieroglyphics Hieroglyphics was the form of writing used in Ancient Egypt that involved pictures
It was also the earliest form of cryptography
They could be written either horizontally or vertically
They could be read from either the left or right hand side
Ideograms represented words
Phonograms spelled the sound of the word Hieroglyphic Alphabet Why Is Cryptography
Important To Us? Why is cryptography important to us? Asymmetric Encryption Similar to symmetric key encryption
Uses two different keys instead of the same key Morse Code Route Ciphers Columnar Ciphers It is one of the most useful human inventions
Privacy is important in our lives
Without cryptography, we would live an uneasy lifestyle and we would feel threatened and unsafe
For example, if it wasn't for security systems, it would be easy for an employee to steal from their boss の Method of transmitting text using on-off tones.
Each character is represented by a series of dots and/or dashes. Plaintext is written on a grid of different dimensions, then read off in a pattern given in the key.
For example, this message is written in a spiral pattern: T S A C T S G
H I S R M S E
I S E E E A J The J at the end is just there to fill up the space. The message is written in rows of a fixed length.
They are read column by column.
The width of the rows are usually defined by a keyword.
For example, the word "zebras" is six letters long. Therefore, the order of the columns will be determined by the alphabetical order of the keyword. In a regular columnar transposition cipher, the empty spaces are filled with random letters. For example, suppose we use the keyword ZEBRAS and the message WE ARE DISCOVERED FLEE AT ONCE. Our grid would look like this:

Z E B R A S
6 3 2 4 1 5
- - - - - -
W E A R E D
I S C O V E
R E D F L E
E A T O N C
E Q K J E U

The six columns are now written out in the scrambled order defined by the keyword:

EVLNE ACDTK ESEAQ ROFOJ DEECU WIREE Columnar Cipher Example Grille Cipher A technique for encrypting a plaintext by writing it onto a sheet of paper through a pierced sheet
A grille is a sheet with holes in random places
A grid is filled with random letters and numbers, that when the grille is placed on top of the grid, it reveals a message through the holes
The grille and the grid are kept separately Review of What We Learned What cryptography is
Why cryptography is important
The history of cryptography
Basics of hieroglyphics
Encryption
Different types of encryption
Decryption
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