2. 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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3. Outline
What is cryptography?
Terminology
Cipher Methods
Substitution Cipher
Transposition Cipher
Exclusive OR
Vernam Cipher
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5. 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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6. 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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7. Terminology
Algorithm Key or Cryptovariable
Cipher or Crypotosystem Keyspace
Ciphertext or Cryptogram Link Encryption
Code Plaintext or Cleartext
Decode Steganography
Decipher Work factor
Encipher
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8. Cipher Methods
Image source: howstuffworks
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9. Answer: WELCOME
Image source: Gareth’s Secret Spy Academy
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10. Cipher Method: Substitution
Initial Alphabet ABCDEFGHIJKLMNOPQRSTUVWXYZ
Encryption 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
This type of substitution is based on a monoalphabetic
substitution, because it only uses one alphabet.
Plaintext M O M
Ciphertext P R P
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11. Substitution Cipher cont’d
Initial Alphabet ABCDEFGHIJKLMNOPQRSTUVWXYZ
Encryption 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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12. Substitution Cipher cont’d
Plaintext 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
Cipher 1 DEFGHIJKLMNOPQRSTUVWXYZABC
Cipher 2 GHIJKLMNOPQRSTUVWXYZABCDEF
Cipher 3 JKLMNOPQRSTUVWXYZABCDEFGHI
Cipher 4 MNOPQRSTUVWXYZABCDEFGHIJKL
More advanced substitution ciphers use two or more alphabets, and are
referred to as polyalphabetic substitutions.
Plaintext T E X T
Ciphertext W K G F
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13. Substitution Cipher cont’d
Plaintext A B C D E F G H I J K L MN O P Q R S T U VWX Y Z
Cipher 1 D E F G H I J K L MN O P Q R S T U VW X Y Z A B C
Cipher 2 G H I J K L MN O P Q R S T U VW X Y Z A B C D E F
Cipher 3 J K L M N O P Q R S T U VWX Y Z A B C D E F G H I
Cipher 4 M N O P Q R S T U VWX Y Z A B C D E F G H I J K L
Plaintext P A S S C T T
Ciphertext S G B E F Z C
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16. 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 GAU L S P A R E NOON E
Ciphertext UKAG L S CAOR P EOS AN E N
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17. Question
What’s another name for the Transposition
Cipher?
A.Pigpen Cipher
B. Permutation Cipher
C. Caesar Cipher
D.Shift Cipher
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18. Cipher Method: XOR
A B Y Text Value Binary Value
0 0 0 CAT as bits 01000011 01000001 01010100
0 1 1
VVV as bits 01010110 01010110 01010110
1 0 1
1 1 0 Cipher 00010101 00010111 00000010
XOR Truth Table Example XOR Encryption
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19. Vernam Cipher
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.
A RUSSIAN ONE-TIME PAD, CAPTURED BY MI5
Image source: http://www.ranum.com/security/computer_security/papers/otp-faq/otp.jpg
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20. Vernam Cipher: Example
Plaintext S A C K G A U L S P A R E N O O N E
Plaintext 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 25 17 20 29 21 20 23 21 24 24 21 44 17 15 18 19 21 15
pad:
After modulo 03 18
subtraction:
Ciphertext: Y Q T C U T W U X X U R Q O R S U O
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21. 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
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22. Henry Osborne
Technology Specialist
Northern Caribbean University
963-7282
henry.osborne@ncu.edu.jm @sicarii13 gplus.to/sicarii13
Editor's Notes
NCU -> Data Security, Java, C++, Networking, PC Repair, Computer ApplicationsVTDI -> Web Programming
If you have any relevant questions during the presentation please feel free to ask….
In light of the increase in computer usage and online activities, the need for the safe and secure transmission of data is paramount. This is where cryptography comes into play.Today, many common IT tools use embedded encryption technologies to protect sensitive information within applications. For example, all the popular Web browsers use built-in encryption features to enable secure e-commerce, such as online banking and Web shopping.
In the study of cryptography there some terms you will need to be acquainted with….Definitions are on the handout that you received earlier….Ciphertextor cryptogram: The encoded message resulting from an encryptionPlaintext or cleartext: The original unencrypted message, or a message that has been successfully decrypted
The Pigpen cipher (sometimes called the Masonic cipher or Freemason's cipher) is a simple substitution cipher exchanging letters for symbols based on a grid (or the "pigpen") surrounding it.
To use a substitution cipher, you substitute one value for another, for example a letter in the alphabet with the letter three values to the right. Or you can substitute one bit for another bit that is four places to its left.Within this substitution scheme, the plaintext MOM would be encrypted into the ciphertext PRP.
The plaintext FACE would be encrypted into the ciphertext IDFH.
Encoding the word TEXT with this cipher yields the ciphertextWKGF
Like the substitution operation, the transposition cipher is simple to understand, but it can, if properly used, produce ciphertext that is difficult to decipher.The transposition cipher (or permutation cipher) simply rearranges the values within a block to create the ciphertext. This can be done at the bit level or at the byte (character) level.
The first bit of plaintext (position 1 of the first byte) becomes the fourth bit (in position 4) of the first byte of the ciphertext. Similarly, the second bit of the plaintext (position 2) becomes the eighth bit (position 8) of the cipher-text, and so on.
To examine further how this transposition key works, look at its effects on a plaintext message comprised of letters instead of bits. Replacing the 8-bit block of plaintext with the example plaintext message presented earlier, “SACK GAUL SPARE NO ONE,” yields the following:
Permutation Cipher
The exclusive OR operation (XOR) is a function of Boolean algebra in which two bits are compared, and if the two bits are identical, the result is a binary 0. If the two bits are not the same, the result is a binary 1.To see how XOR works, consider an example in which the plaintext is the word “CAT.” The ASCII binary representation of the plaintext is “01000011 01000001 01010100”. In order to encrypt the plaintext, a key value should be selected. In this case, the bit pattern for the letter “V” (01010110) is used, and is repeated for each character to be encrypted, written left to right. Performing the XOR operation on the two bit streams (the plaintext and the key) produces the cipher as shown.
The pad in the name comes from the days of manual encryption and decryption when the key values for each ciphering session were prepared by hand and bound into an easy-to-use form—that is, a pad of paper.A one-time pad is a cryptosystem invented by Vernam. It's a very simple system and is unbreakable if used correctly.
Using the pad values and the ciphertext, the decryption process works as follows: “Y” becomes the number 25, from which we subtract the pad value for the first letter of the message, 06. This yields a value of 19, or the letter “S”. Where the ciphertext letter is “C” and the pad value is 18. Subtracting 18 from 3 yields negative 15. Since modulo 26 is employed, which requires that all numbers are in the range of 1–26, you must add 26 to the negative 15. This operations gives a sum of 11, which means that fourth letter of the message is “K.”
To use a substitution cipher, you substitute one value for another, or you can substitute one bit for another bit x places to its left or right.The transposition cipher simply rearranges the values within a blockThe exclusive OR (XOR) operation is a function of Boolean algebra in which two bits are compared, and if the two bits are identical, the result is a binary 0