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The History of Cryptography

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An early form of a substitution cipher appears in a text based on manuscripts ... Then a message that Piglet wants to send is put into binary and this number M is ... – PowerPoint PPT presentation

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Title: The History of Cryptography


1
The History of Cryptography
  • From 500 B.C.

2
  • Cryptography
  • Cryptanalysis
  • Codes
  • Ciphers
  • Keys

3
The Early Breakthroughs
  • Ancient Greeks - shaved the head of slaves
  • - used a transposition
    cipher by wrapping leather round a
    scytale.
  • An early form of a substitution cipher appears in
    a text based on manuscripts from the 4th Century
    B.C.
  • The Kama Sutra! women should study
    mlecchita-vikapla.
  • Julius Caesar also used cryptography he
    invented the Caesar shift cipher

4
The Arab Cryptanalysists
  • Cryptographers were winning!

    - Caesar shift cipher has only 26 permutations

    - but random substitution has 26!
  • This began to change around 750 A.D. where in the
    Islamic world were monoalphabetic ciphers were
    already in use.
  • Religious scholars were analysing the texts of
    the Prophet Muhammad and discovered that some
    letters occurred more frequently than others!
    This led to the discovery of frequency analysis
    to solve monoalphabetic ciphers.
  • Im sure you all know the letter E is most
    prevalent in the English language its frequency
    is 12.7.

5
The Europeans
  • The Europeans were far behind. Monks were the
    only people who studied cryptanalysis and slowly
    they reintroduced it to the Western world.
  • By the 15th century, about 700 years after the
    Arabs, frequency analysis is discovered.
  • Mathematically speaking, a breakthrough was
    needed for cryptography. They have added null
    letters, enciphered spaces and misspelled words
    to distort frequency, but it is essentially the
    same.
  • This breakthrough came from several men, but the
    credit was given to Blaise de Vigenere. He
    introduced a polyalphabetic cipher, published in
    1586 and unbroken until the late 19th century.

6
A B C D E F G H I J K L M N O P Q R S T U
V W X Y Z A A B C D E F G H I J K L M N O P Q R
S T U V W X Y Z B B C D E F G H I J K L M N O P
Q R S T U V W X Y Z A C C D E F G H I J K L M N
O P Q R S T U V W X Y Z A B D D E F G H I J K L
M N O P Q R S T U V W X Y Z A B C E E F G H I J
K L M N O P Q R S T U V W X Y Z A B C D F F G H
I J K L M N O P Q R S T U V W X Y Z A B C D E G
G H I J K L M N O P Q R S T U V W X Y Z A B C D E
F H H I J K L M N O P Q R S T U V W X Y Z A B C
D E F G I I J K L M N O P Q R S T U V W X Y Z A
B C D E F G H J J K L M N O P Q R S T U V W X Y
Z A B C D E F G H I K K L M N O P Q R S T U V W
X Y Z A B C D E F G H I J L L M N O P Q R S T U
V W X Y Z A B C D E F G H I J K M M N O P Q R S
T U V W X Y Z A B C D E F G H I J K L N N O P Q
R S T U V W X Y Z A B C D E F G H I J K L M O O
P Q R S T U V W X Y Z A B C D E F G H I J K L M N
P P Q R S T U V W X Y Z A B C D E F G H I J K L
M N O Q Q R S T U V W X Y Z A B C D E F G H I J
K L M N O P R R S T U V W X Y Z A B C D E F G H
I J K L M N O P Q S S T U V W X Y Z A B C D E F
G H I J K L M N O P Q R T T U V W X Y Z A B C D
E F G H I J K L M N O P Q R S U U V W X Y Z A B
C D E F G H I J K L M N O P Q R S T V V W X Y Z
A B C D E F G H I J K L M N O P Q R S T U W W X
Y Z A B C D E F G H I J K L M N O P Q R S T U V
X X Y Z A B C D E F G H I J K L M N O P Q R S T U
V W Y Y Z A B C D E F G H I J K L M N O P Q R S
T U V W X Z Z A B C D E F G H I J K L M N O P Q
R S T U V W X Y
Vigenere Cipher
7
World War I
  • Due to the invention of the radio, allied
    forces were intercepting hundreds of messages a
    day.
  • Arthur Zimmerman, the German foreign minister was
    hoping to keep the U.S.A. out of the war.
  • His telegram was intercepted and passed to Room
    40.
  • This persuaded the Americans into the war.
  • Room 40 were criticised in a cover up story.

8
World War II
  • The Enigma is probably the best known cipher of
    all.
  • The Germans believed it unbreakable, it was a
    machine of rotating wheels, electrical contacts
    and wires that could be swapped giving rise to
    10,000,000,000,000,000 keys.
  • Poland however felt they could be threatened by
    Germany or Russia.
  • The Germans, however increased the choice of
    wheels, so increasing the number of keys that
    could be used.

9
World War II and Bletchley Park
  • Poland did not have the capacity to cope with
    Enigma any more.
  • Room 40 moved to Bletchley Park and became home
    to over 1000 staff working on decrypting German
    messages as the war began.
  • Here Alan Turing became famous for the work he
    did on the Enigma, carrying on Rejewskis work to
    gain valuable information for the Allies.
  • Also, a world first, an a programmable computer
    named Colossus was built to break Lorenz, a
    cipher used personally by Hitler. Another
    secret only revealed years later.

10
Public Key Cryptography
  • After the war cryptography began making its way
    into everyday life, as did computers. Gradually a
    problem arose.
  • How to distribute keys safely?
  • The idea was thought of by Diffie, Hellman and
    Merkle in 1976. They came up with the idea of
    needing a public key so a message can be
    encrypted, and a private key so that you can
    decrypt the message using an asymmetric cipher.
  • In the end it was a different team who solved it
    Rivest Shamir and Adleman who came up with RSA.

11
How does it work?
  • Well you should all be able to remember
  • Core A anyone?
  • Winnie the pooh picks two, very large prime
    numbers, p and q.
  • p x q N
  • He also picks another number e. Together these
    numbers are his public key.
  • Then a message that Piglet wants to send is put
    into binary and this number M is encrypted
    according to C Me (mod N) and C is sent to
    Winnie the pooh.
  • This is impossible to work out without the
    private key as long as the primes used for p and
    q are big enough.
  • The private key is d, worked out from p and q
    using Euclids algorithm.

12
The rest.
  • It was recently discovered, much like the first
    programmable computer, that actually GCHQ first
    found RSA, four years earlier, but kept it
    secret.
  • RSA is responsible for protecting most
    communications and is widely used as there is
    still no shortcut to factoring a large number.
  • There is an ongoing debate about whether strong
    encryption should be available to everyone for
    personal privacy or if it shouldnt - so law
    enforcement can still get information from
    criminals.

13
The End
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