Cryptography &
Encryption
Secret Codes &
The Advance of Technology
Copyright © 2008 by Helene G. Kershner
Cryptography & Encryption
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Since the dawn of written language people have used
codes.
Secret CODE: “a system used for brevity or secrecy of
communication, in which arbitrarily chosen words,
letters, or symbols are assigned definite meanings.”
http://dictionary.reference.com/
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“Codes and ciphers are forms of secret communication. A code
replaces words, phrases, or sentences with groups of letters or
numbers
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A cipher rearranges letters or uses substitutes to disguise the message.”
http://www.42explore2.com/codes.html
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A cipher is an algorithm for performing coding (encryption) and decoding
(decryption) character. http://en.wikipedia.org/wiki/Encryption
Copyright © 2008 by Helene G. Kershner
Cryptography & Encryption
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Who uses secret codes?
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Governments, military, businesses
Doctors, computer uses, almost everyone
Why bother?
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To keep information private
To protect information
To protect ourselves or to initiate action
 "One if by land; two if by sea" in “Paul Rever’s Ride” in
Longfellow’s poem. http://en.wikipedia.org/wiki/Code_(cryptography)
 The BBC broadcast “personal” messages such as: “The
princess wears red shoes” & “Mimi's cat is asleep under the
table” to direct actions by the French resistance during WW II.
http://en.wikipedia.org/wiki/Code_(cryptography)
Copyright © 2008 by Helene G. Kershner
Cryptography & Encryption
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Long and mysterious history
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Codes used by ancient Hebrews, Babylonians, Egyptions,
Greeks and Arabs.
Caesar cipher – a code developed by Julius Caesar that
substituted each letter of the Roman alphabet for a letter 3positions down the list.
President Jefferson and Lewis & Clark communicated in code
when planning for their expedition.
The Morse Code is a set of dots and dashes that represents
words.
Used heavily in both World Wars
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British built one of the first computers called Colossus to defeat the German
coding system called Enigma.
Navajo “code talkers” served with the Marines in the Pacific
http://en.wikipedia.org/wiki/Encryption
Copyright © 2008 by Helene G. Kershner
Cryptography & Encryption
How might they work?
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The Apple is Red
Abcdefghijklmnopqrstuvwxyz
Using the Caesar cipher substitute for letters 3-down the
alphabet
THE APPLE is Red = WKH DSSOH ….
http://en.wikipedia.org/wiki/Encryption
Copyright © 2008 by Helene G. Kershner
Cryptography & Encryption
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Taken on new importance in the Computer Age
“Encryption is the process of obscuring information to
make it unreadable without special knowledge.
To be sure a message is secret we need to know that :
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the communication is secure
it is received by the right “people”
it can be decrypted (or decipher)
In other words, we must verify the integrity and
authenticity of a message.
http://en.wikipedia.org/wiki/Encryption
Copyright © 2008 by Helene G. Kershner
Cryptography & Encryption
The Government’s Need to Know
Vs
The Right to Privacy
Are these two ideas necessarily at odds?
Which should have higher priority?
Copyright © 2008 by Helene G. Kershner
Cryptography & Encryption
In the mid-1970s, strong encryption
went from government agencies to
the public domain.
WHY?
Copyright © 2008 by Helene G. Kershner
Cryptography & Encryption
Where is it used if not by the government? Encryption is now
widely-used anywhere where there are computers.
 Password access to Internet sites
 Internet shopping, e-commerce
 Cellular messages
 Online banking and ATMs
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Code Makers & Code Breakers (3) The Enigma -- History
Channel http://www.youtube.com/watch?v=cGPRClA-lok
Code Makers & Code Breakers (4) - American Cryptology -History Channel
http://www.youtube.com/watch?v=GFLZyifnMuY&feature=related
http://secretcodebreaker.com/videos.html
Copyright © 2008 by Helene G. Kershner