Transcript Encryption - Ms. Waldron

Encryption: A Brief History
Author:
Margery Waldron
Encryption
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Encryption is the process of converting
messages and documents into a secret
code to ensure privacy.
Encryption has fascinated people of all
ages throughout history
Encryption is used today in many fields
including the internet, banking and CIA.
Cryptography
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Cryptography is the field of computer science
that studies encryption and decryption, which
is the process of “breaking the code”.
Code: a “code” uses substitute words,
numbers or symbols in place of each word in
the secret message.
Cipher: a “cipher” uses numbers or symbols
for every letter in the secret message
Polybius
Polybius: A Greek historian captured
during Roman conquest of Greece in
168 BC who made a cipher to send
secret messages
Polybius’ secret code was called the
Polybius’ Square Key
Polybius’ Square Key
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1
A
B C D
E
2
F
G H I
J
3
K
L M N O
4
P
Q R S T
5
U
V W X Y/Z
To write a message using this
code, simply write the two
numbers that intersect at the
letter you want. For example
51 = U.
Using this cipher, figure out the
message below:
55-35-51’-43-15 11 22-15-3424-35-51-44!
Caesar's Shift
Caesar’s Shift Cipher: Roman Emperor Julius Caesar invented this cipher
which gives a number to each letter of the alphabet by shifting the
alphabet three places to the right:
A B C D E F G H I J K L M N
3 4 5 6 7 8 9 10 11 12 13 14 15 16
O P Q R S T U V W X Y Z
17 18 19 20 21 22 23 24 25 26 27 28
Using Caesar’s cipher, decode this:
10-17-25 6-17 27-17-23 14-11-13-7 22-10-11-21 5-11-18-10-7-20?
Alan Turing
Alan Turing: an English math scholar who worked as a
code breaker for the Government Code and Cypher
School during WWII. He is responsible for breaking the
German’s “Enigma code” used to communicate with
their submarines which helped turn the war around for
the allies. He went on to design one of the first
computers called the “turing machine” in 1946.
He was also an Olympic long distance runner!
Prime numbers & Cryptography
Cryptographers use prime numbers to encrypt code
because when they are large, they are very hard to locate.
In 1977, a group of cryptographers challenged other
cryptographers to find the key to their brand-new code.
The only way to do it was to find the prime factors of a
certain number that was 129 digits long!! At that time, the
cryptographers figured it would take about 40 quadrillion
(40 x 10 15) years for others to solve the puzzle and crack
the code. This problem was solved in the spring in 1994 in
a time span of just 8 months by 160 computers working
together via the Internet on a solution!!
Beale's Buried Treasure
During the 19th century, a young man named Thomas Jefferson Beale
appeared in Lynchburg, Virginia. After two years, he left an iron box
with a trusted friend before leaving again. Beale told the friend that
the box was not to be opened until 10 years had passed without his
return.
The decade passed with no sign of Beale. The box was opened and
inside it were papers that described a spectacular buried treasure and
directions on where to find it. However, the directions were nothing
but three pages of numbers! (These numbers are printed in their
entirety in Paul Hoffman’s book, Archimedes’ Revenge if you want to
have a look!) The owner of the box was unable to decipher the code
and when he died 41 years later, he left it with another man named
James Ward.
Beale's Buried Treasure
Years later, Ward was able to decipher one of the pages because
he discovered that Thomas Jefferson Beale had used for a cipher
key: the Declaration of Independence! By numbering each word of
the Declaration of Independence, Ward hit upon the solution and
was able to decipher the entire page. However, that page told only
that the treasure consisted of thousands of pounds of gold and
silver and millions of dollars’ worth of jewels, not where it was
buried.
Cryptographers have been trying for over 170 years, without
success, to decipher the other pages or find the treasure. Even
today, using modern computers, the cipher remains a mystery.
Beale's Buried Treasure
Declaration of Independence
When in the course of human events it
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becomes necessary for...
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Ms. Waldron's Secret Message
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You are going to be given a file called
secretcode.dat that contains a secret
message.
You will create a class called Cypher
that contains your substitution Cipher.
You will write a java application that
uses the Cypher class to decrypt the
secret message.
Mrs. Waldron's Buried Treasure
The secret message is written using a
substitution cipher. That is every letter
in the Alphabet has been changed to a
different letter. You need to substitute
letters of the alphabet with what you
guess is the corresponding encoded
letter. You can reassign the letter if you
change your mind.
Ms. Waldron’s Secret Message
The templates for the Cypher Class
and Decrypt.java are on our web site.
Now we will have a demonstration…