Cryptography

CRYPTOGRAPHY

Henry OsborneTechnology SpecialistNorthern Caribbean University

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Presenter Profile Education

Dip. Applied Computer Science, Jamaica Advanced Computer Systems

B.Sc. Information Science, Northern Caribbean University

M.Sc. Management Information System (Security Concentration), Nova Southeastern University – candidate

Security+ candidate

Professional Experience Technology Specialist: Dept. of Computer & Information Sciences

(NCU)

Instructor: NCU, VTDI

Internet Services Coordinator: Round Hill Hotel & Villas

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Outline

What is cryptography? Terminology Cipher Methods

Substitution Cipher Transposition Cipher Exclusive OR Vernam Cipher

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What is Cryptography?

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Cryptography, which comes from the Greek words kryptos, meaning “hidden,” and graphein, meaning “to write,” is the process of making and using codes to secure the transmission of information.

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Yet it may roundly be asserted that human ingenuity cannot concoct a cipher which human ingenuity cannot resolve.

EDGAR ALLAN POE, THE GOLD BUG

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Terminology Algorithm Cipher or Crypotosystem Ciphertext or Cryptogram Code Decode Decipher Encipher

Key or Cryptovariable Keyspace Link Encryption Plaintext or Cleartext Steganography Work factor

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Cipher MethodsImage source: howstuffworks

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Answer: WELCOMEImage source: Gareth’s Secret Spy Academy

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Cipher Method: Substitution

Initial Alphabet 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 ZEncryption Alphabet 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

Plaintext M O M

Ciphertext P R P

This type of substitution is based on a monoalphabetic substitution, because it only uses one alphabet.

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Substitution Cipher cont’d

Initial Alphabet 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 ZEncryption Alphabet 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

Plaintext F A C E

Ciphertext I D F H

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Substitution Cipher cont’dPlaintext 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 ZCipher 1 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 CCipher 2 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 FCipher 3 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 ICipher 4 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

Plaintext T E X TCiphertext W K G F

More advanced substitution ciphers use two or more alphabets, and are referred to as polyalphabetic substitutions.

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Substitution Cipher cont’d

Plaintext P AS S C T T

Plaintext A B C D E F G H I J K L MN O P Q R S T U V WX Y ZCipher 1 D E F G H I J K L MN O P Q R S T U V WX Y Z A B CCipher 2 G H I J K L MN O P Q R S T U V WX Y Z A B C D E FCipher 3 J K L M N O P Q R S T U V WX Y Z A B C D E F G H ICipher 4 M N O P Q R S T U V WX Y Z A B C D E F G H I J K L

Ciphertext S GB E F Z C

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Cipher Method: Transposition

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Transposition Cipher cont’d

Key pattern: 1 -> 4, 2 -> 8, 3 -> 1, 4 -> 5, 5 -> 7, 6 -> 2, 7 -> 6, 8 -> 3

Plaintext: 00100101 01101011 10010101 01010100

Bit Locations 8 7 6 5 4 3 2 1 8 7 6 5 4 3 2 1 8 7 6 5 4 3 2 1 8 7 6 5 4 3 2 1

Plaintext 0 0 1 0 0 1 0 1 0 1 1 0 1 0 1 1 1 0 0 1 0 1 0 1 0 1 0 1 0 1 0 0

Ciphertext 0 0 0 0 1 0 1 1 1 0 1 1 1 0 1 0 0 1 0 0 1 1 0 1 0 1 1 0 0 0 0 1

Reading from right to left in the example above

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Transposition Cipher cont’d

Key pattern: 1 -> 4, 2 -> 8, 3 -> 1, 4 -> 5, 5 -> 7, 6 -> 2, 7 -> 6, 8 -> 3

Plaintext: “SACK GAUL SPARE NO ONE”

Bit Locations 8 7 6 5 4 3 2 1 8 7 6 5 4 3 2 1 8 7 6 5 4 3 2 1 8 7 6 5 4 3 2 1

Plaintext S A C K G A U L S P A R E N O O N E

Ciphertext U K A G L S C A O R P E O S A N E N

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Question

What’s another name for the Transposition Cipher?

A.Pigpen CipherB. Permutation CipherC. Caesar CipherD.Shift Cipher

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Cipher Method: XOR

Text Value Binary Value

CAT as bits 01000011 01000001 01010100

VVV as bits 01010110 01010110 01010110

Cipher 00010101 00010111 00000010

A B Y

0 0 0

0 1 1

1 0 1

1 1 0

XOR Truth Table Example XOR Encryption

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Vernam Cipher

A RUSSIAN ONE-TIME PAD, CAPTURED BY MI5

Also known as One-time Pad

Developed by Gilbert Vernam (AT&T engineer) in 1917

Uses a set of characters only one time for each encryption process

To use a one-time pad, you need 2 copies of the "pad" which is a block of random data equal in length to the message you wish to encode.

Image source: http://www.ranum.com/security/computer_security/papers/otp-faq/otp.jpg

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Vernam Cipher: Example

Plaintext S A C K G A U L S P A R E N O O N EPlaintext value: 19 01 03 11 07 01 21 12 19 16 01 18 05 14 15 15 14 05

One-time pad text: F P Q R N S B I E H T Z L A C D G J

One-time pad value: 06 16 17 18 14 19 02 09 05 08 20 26 12 01 03 04 07 10

Sum of plaintext and pad:

25 17 20 29 21 20 23 21 24 24 21 44 17 15 18 19 21 15

After modulo subtraction:

03 18

Ciphertext: Y Q T C U T W U X X U R Q O R S U O

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Summary What is cryptography?

Cryptography is the process of making and using codes to secure the transmission of information.

Key Terms Ciphertext, Plaintext, Key, etc

Cipher Methods Substitution Cipher Transposition Cipher (or permutation cipher) Exclusive OR Vernam Cipher

[email protected] gplus.to/sicarii13@sicarii13

Henry OsborneTechnology Specialist

Northern Caribbean University963-7282