Transcript Slide 1

What is Cryptography?
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What is Cryptography/ Cryptology?

The art of protecting information by
transforming it (encrypting it) into an
unreadable format, called cipher text.
 Only those who possess a secret key can
decipher (or decrypt) the message into plain
text.
 Encrypted messages can sometimes be
broken by cryptanalysis, also called
codebreaking, although modern cryptography
techniques are virtually unbreakable.
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What is Cryptography?
As the Internet and other forms of
electronic communication become more
prevalent, electronic security is
becoming increasingly important.
 Cryptography is used to protect e-mail
messages, credit card information, and
corporate data.

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Break this code
20-15-4-1-25
12-5-1-18-14
19
25-15-21 23-9-12-12
1-2-15-21-20 3-15-4-5-
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Cipher Text
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25-15-21 23-9-12-12
1-2-15-21-20 3-15-4-5-19
Text that has been transformed into an
unreadable format.
 Code
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In cryptology, code means substituting a
meaningful word or phrase with another word or
phrase to change or hide meaning
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20-15-4-1-25
12-5-1-18-14
 Cipher text
What numbers occur most
frequently in the ciphertext?
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Frequency analysis is the process by
which the frequency of a letter in an
encoded messages is compared with the
frequency of letters in English words.
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What numbers occur most
frequently in the ciphertext?
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For instance, the letter E occurs most
often in English words, so if the letter W
occurs most often in ciphertext, then it is
likely that E has been replaced by W.
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See Handout
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Using the Frequency Table Decode
this Message
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TFNRIUJ UZV
DREP
KZDVJ
SVWFIV KYVZI UVRKYJ;
KYV
MRCZREK
EVMVI
KRJKV
FW
UVRKY
SLK
FETV.
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Caesar cipher

A Caesar cipher is a coding system in which
letters are replaced by letters a certain
distance ahead in the alphabet.
 Julius Caesar is thought to have used this
method to communicate with officers in the
Roman army.
 When sending a message, Caesar would
inform his generals what the shift was, so they
would be the only ones who could read the
encrypted message.
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Caesar Cipher
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Caesar Cipher –Shift of 7
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Encrypt this message
using the Caesar shifterShifting 7
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Coded
ROME IS THE
GREATEST EMPIRE.
Decode this message
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YVTL DHZ UVA IBPSA
PU H KHF.
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English

You may have also used logic when decoding
the message.
 Some may have noticed the one-letter word h
that appears near the end of the message.
 Since this letter must represent either a or I
(these are the only two single-letter English
words), students can determine the possible
shifts and see which one works for the
remainder of the message.
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Answers
Correct Code =YVTL PZ AOL
NYLHALZA LTWPYL.
 Decoded message = Rome was not built
in a day.

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To Check…
Go To:
http://illuminations.nctm.org/ActivityDetail.a
spx?id=5
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To Check the Cipher

CryptoClub

http://cryptoclub.math.uic.edu/shiftcipher/shi
ftcipher.htm
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Caesar Cipher named after Julius
Caesar
Who was he? Where was he from? And
when did he live?
 Julius Caesar was the Emperor of Rome.
He lived from 100-44 B.C.

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The Caesar Cipher is based on shifting
the letters in the alphabet a certain
number of spaces. How many shifts are
possible?
 The Caesar cipher has 25 possible
shifts. A shift of 26 or more will simply
repeat one of the shifts of 1-25.

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Why do you think this method was used
by Julius Caesar? During his time, how
effective do you think it was to send
secret messages?
 This was probably sufficient during
Caesar’s time, but it is insufficient today
because of advanced code breaking
methods.

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Would this method provide adequate
security today or would a code using this
method be easily broken?
 No, this would be insufficient today
because of advanced code breaking
methods.

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Explain why the number of total shifts
(from the second question) is the weak
point of the Caesar Cipher.
 Because there are only 25 possible
shifts, a person could test each possible
shift to determine if an encoded
message uses the Caesar cipher.

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Try one on your own
Encode a “common” message using the
Caesar Cipher and any shift you choose
and exchange the ciphertext with a
classmate.
 The student receiving the ciphertext
should decode the message and be able
to tell what shift was used.

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Go back to …
http://illuminations.nctm.org/ActivityDetail.a
spx?id=5
Walk through the Instructions
 Try Explorations


Crack the Code lxwpajcdujcrxwb
Make sure you type in only lower case—type
in encoded message box and click decode
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In Excel
Secret Messages
 Plot the Secret Location

See Handouts for Directions
Answers:
Secret messages
Plot the location
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Methods of Cryptography
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Substitution
 Replacing each letter with a different letter or symbol (a=@, b=J, c=2 so that “a cat” =
“@ 2J@”)
Transposition
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Steganography
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Hiding a message (example: invisible inks, Herodotus tattooed messages on a
shaved slave’s head and waited for the hair to re-grow to hide his messages)
Mathematical
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Rearranging the order of letters of the words of a message. (example: “the letters in
each word get moved around = eth ttseelr ni ceah drow etg veodm uarndo”)
Uses advanced formulas to encrypt text
Computer or Mechanically Assisted

Using complex algorithms and any single or combination of the mathematical,
transposition, substitution and steganography to encrypt plain text.
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The Enigma Machine
 The
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most famous mechanical encryption
device in history.
 INSERT PICUTRE OF MACHINE HERE
WITH LINK TO YOU TUBE VIDEO
Cryptanalyst: Job Description
Creates algorithms for transforming plain
text into unreadable information (cipher
text), or for decoding encrypted
information
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Cryptanalyst: AKA
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AKA
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AKA
Cryptographer
Chronologic
Technician
Chronologic
Linguist
Symbolist
Decipherer
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Information Security
Expert
Intelligence Agent
Intelligence Officer
Information Security
Engineer
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Cryptanalyst: Salary
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$55,000 - $130,000.00 +
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Cryptanalyst: Education
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Entry Level: Undergraduate:
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Math
Computer Science
Foreign Languages
Engineering
Telecommunications
Computer Programming Languages
Political Science
Mid and High Level: Masters +
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Math
Computer Science
Engineering
Information Assurance / Information Security
Source:
http://careersthatdonotsuck.com/2007/02/24/careers-profileCopyright ETPRO
cryptologist/
The Need
 Copyright
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Personal Email
Businesses
Government
Military
 Credit
Card Processing
 Password Protection
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RSA tokens: for business and games (like
Warcraft)
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Protection
 Security of communications for
Legal Problems
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Digital Millennium Copyright Act (1998)
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Cryptanalyst argue that the algorithms should be published so that they
can be improved and used. Only the keys should remain a secret.
The first arrest was Dmitry Sklyarov, whose dissertation work and
subsequent work with a Russian book reader company identified
weaknesses in the protection of PDF files.
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Intended to provide law enforcement with a tool to go after
piracy and file sharing (media like music, movies, and
software)
Made it illegal to use cryptanalytic techniques to get around the
copyright protection methods (called Digital Rights
Management)
Unintended result was to limit research and research sharing in
the Cryptanalyst field for fear that their work might violate this
law.
Your are the Cryptanalyst!
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Create your own algorithm for encrypting a
message!
Substitution
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Transposition


Hiding a message (example: invisible inks, Herodotus tattooed messages on a shaved
slave’s head and waited for the hair to re-grow to hide his messages)
Mathematical

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Rearranging the order of letters of the words of a message. (example: “the letters in each
word get moved around = eth ttseelr ni ceah drow etg veodm uarndo”)
Steganography

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Replacing each letter with a different letter or symbol (a=@, b=J, c=2 so that “a cat” = “@
2J@”)
Uses advanced formulas to encrypt text
Computer or Mechanically Assisted

Using complex algorithms and any single or combination of the mathematical, transposition,
substitution and steganography to encrypt plain text.
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Number Theory
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Number Theory Applet 11. Letter Frequency Analysis
Calculator
 http://www.wiley.com/college/mat/gilbert139343/jav
a/java11_s.html
Black Chamber
 http://www.simonsingh.net/The_Black_Chamber/fre
quencyanalysis.html
Code Breaking Software & simulations
 http://www.richkni.co.uk/php/crypta/freq.php
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Remainder of Time Visit
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America's Crypto Kids (K-12)
National Security Agency (NSA)
http://www.nsa.gov/kids/
CIA Kids’ Page (K-12)
Central Intelligence Agency (CIA)
https://www.cia.gov/kids-page/index.html
FBI Kids’ Page
Federal Bureau of Investigation (FBI)
http://www.fbi.gov/fbikids.htm
Future State
U.S. Department of States
http://www.future.state.gov/
Ready Kids
Department of Homeland Security
http://www.ready.gov/kids/home.html
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