1. Cryptography and Network Security
Professor Dr. M. Ismail Jabiullah
Department of Software Engineering
Daffodil International University

2. Topics Cryptography Cryptographic Terms Cryptographic Components
Encryption/Decryption
Types of Cryptographic Algorithms
Symmetric Key Cryptography
Caesar Cipher
Concepts
Problems
Traditionally information security provided by physical (eg. rugged filing cabinets with locks) and administrative mechanisms (eg. Personnel screening procedures during hiring process).
Growing computer use implies a need for automated tools for protecting files and other information stored on it.
This is especially the case for a shared system, such as a time-sharing system, and even more so for systems that can be
accessed over a public telephone network, data network, or the Internet.

3. Text space for writing documents1 2 3 4 5 6 7 8 9 10 11 12 A B C D E F G H I J K L M 13 14 15 16 17 18 19 20 21 22 23 24 25 N O P Q R S T U V W X Y Z

4. ~ Caesar Cipher Ciphertext : GSQTYXIV Plaintext : COMPUTER C 2 K = 4 6
Plaintext in
KKey Algorithm
Ciphertext in
Key
Algorithm
Plaintext in
Text
Number ~ C 2
K = 4 6 G O 14 18 S M 12
Forward 16 Q
Backward P 15 19 T U 20 24 Y 23 X E 4 8 I R 17 21 V

5. Caesar Cipher
Perform the Encryption/decryption operation with key value 5
COME HERE
PAY MORE MONEY
Traditionally information security provided by physical (eg. rugged filing cabinets with locks) and administrative mechanisms (eg. Personnel screening procedures during hiring process).
Growing computer use implies a need for automated tools for protecting files and other information stored on it.
This is especially the case for a shared system, such as a time-sharing system, and even more so for systems that can be
accessed over a public telephone network, data network, or the Internet.

6. Caesar Cipher Julius Caesar Process:
Replace each letter of the alphabet with letter standing three places further down the alphabet.
The alphabet is wrapped around, so that the letter following Z is A.
Advantages:
Simply try all possible 25 ways.
Key values are within 25.
Characteristics
The encryption and decryption algorithms are known.
There are only 25 keys to try.
The language of the plaintext is known and easily recognizable.
Traditionally information security provided by physical (eg. rugged filing cabinets with locks) and administrative mechanisms (eg. Personnel screening procedures during hiring process).
Growing computer use implies a need for automated tools for protecting files and other information stored on it.
This is especially the case for a shared system, such as a time-sharing system, and even more so for systems that can be
accessed over a public telephone network, data network, or the Internet.

7. Caesar Cipher

8. Cryptography Components
Plaintext
Sender
Receiver
Encryption Algorithm
Ciphertext
Decryption Algorithm
Traditionally information security provided by physical (eg. rugged filing cabinets with locks) and administrative mechanisms (eg. Personnel screening procedures during hiring process).
Growing computer use implies a need for automated tools for protecting files and other information stored on it.
This is especially the case for a shared system, such as a time-sharing system, and even more so for systems that can be
accessed over a public telephone network, data network, or the Internet.

9. Key Elements Plaintext = P Encryption Algorithm = E
Decryption Algorithm = D
Ciphertext = C
Key = K
Traditionally information security provided by physical (eg. rugged filing cabinets with locks) and administrative mechanisms (eg. Personnel screening procedures during hiring process).
Growing computer use implies a need for automated tools for protecting files and other information stored on it.
This is especially the case for a shared system, such as a time-sharing system, and even more so for systems that can be
accessed over a public telephone network, data network, or the Internet.

10. Symmetric-key Cryptography Or Single Key Cryptography
Private Key Cryptography
Traditionally information security provided by physical (eg. rugged filing cabinets with locks) and administrative mechanisms (eg. Personnel screening procedures during hiring process).
Growing computer use implies a need for automated tools for protecting files and other information stored on it.
This is especially the case for a shared system, such as a time-sharing system, and even more so for systems that can be
accessed over a public telephone network, data network, or the Internet.

11. Public-key Cryptography
Traditionally information security provided by physical (eg. rugged filing cabinets with locks) and administrative mechanisms (eg. Personnel screening procedures during hiring process).
Growing computer use implies a need for automated tools for protecting files and other information stored on it.
This is especially the case for a shared system, such as a time-sharing system, and even more so for systems that can be
accessed over a public telephone network, data network, or the Internet.
Public-key algorithms are more efficient for short messages.

12. Signing the Whole Document
Traditionally information security provided by physical (eg. rugged filing cabinets with locks) and administrative mechanisms (eg. Personnel screening procedures during hiring process).
Growing computer use implies a need for automated tools for protecting files and other information stored on it.
This is especially the case for a shared system, such as a time-sharing system, and even more so for systems that can be
accessed over a public telephone network, data network, or the Internet.

13. Cryptography Algorithms in the world are in two types:
Symmetric-key Cryptography Algorithms or
Secret key Cryptography Algorithms or
Single key Cryptography Algorithms
Asymmetric-key Cryptography Algorithms or
Public key Cryptography Algorithms or
Public-Private key Cryptography Algorithms
Traditionally information security provided by physical (eg. rugged filing cabinets with locks) and administrative mechanisms (eg. Personnel screening procedures during hiring process).
Growing computer use implies a need for automated tools for protecting files and other information stored on it.
This is especially the case for a shared system, such as a time-sharing system, and even more so for systems that can be
accessed over a public telephone network, data network, or the Internet.

14. Problems
Perform Encryption and Decryption for at least 3 plaintext with key values more than 15.
Traditionally information security provided by physical (eg. rugged filing cabinets with locks) and administrative mechanisms (eg. Personnel screening procedures during hiring process).
Growing computer use implies a need for automated tools for protecting files and other information stored on it.
This is especially the case for a shared system, such as a time-sharing system, and even more so for systems that can be
accessed over a public telephone network, data network, or the Internet.

15. That’s All For Today