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Cryptography

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by

Paul Wees

on 14 December 2013

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Transcript of Cryptography

Caesar Cipher
Developed in 50 B.C. by Julius Caesar [1]
Communication
Shift cipher
Example encrypting APPLE
Introduction
Caesar Cipher
Transposition Cipher
Affine Cipher
Hashes
Public Key Cryptography
Cryptography
Paul Wees

APPLE as plaintext
XMMIB is the ciphertext
Transposition Cipher(s)
Seen in use as early as 4th century B.C. by the Spartans [1]
Jumbled plaintext
Spartan Scytale Cipher
Zig-zag Cipher
Spartan Scytale Cipher
Parchment paper originally used [1]
Diameter
Unraveling
Example encrypting WALKING IN THE PARK ON A WINTERS EVENING
Ciphertext: WIRNE ANKTN LTOEI KHNRN IEASG NPWEX GAIVX
Zig-zag Cipher
Breaks plaintext into two halves
Top half
Bottom half
Example encrypting WALKING IN THE PARK ON A WINTERS EVENING
Ciphertext: WLIGNH PROAIT REEIGA KNITEA KNWNES VNN
Affine Cipher
Substitution cipher
Mathematically creates the "randomness"
Encrypting: y = (ax + b) MOD 26 [1]
Decrypting: x = a^-1(y - b) MOD 26 [1]
Example encrypting CRYPTO a = 9 b = 2
C = 2, R = 17, Y = 24, P = 15, T = 19, O = 14
Ciphertext: UZKHRY
Hashes
One-way encryption [1]
Useful for signing messages
Users can send messages unencrypted if a hash is sent first
Example encrypting TOP SECRET MESSAGE WE ARE BEING SPIED ON
Hash value: KAFYB
Public Key Cryptography
Algorithms and encryption keys are made public
Trusting the math of the algorithm to protect private decryption key [1]
Example public key crypto algorithms
RSA
PGP
SSL
Diffie-Hellman
References
1. Barr, T. (2002). Invitation to cryptology. Upper Saddle River, New Jersey: Prentice Hall.
Full transcript