Lecturer 2:

1. Lecturer 2: Classical Cryptography SubstitutionCipher Newroz N. Abdulrazaq Science College- Department of Computer Science & I.T. newroz.abudlrazaq@su.edu.kurd Mobile: 07504052680

2. Cryptology What we Learned From the Last Lecturer? • Cryptanalysis • Cryptography • Encryption • Decryption

3. Today Lecturer Outlines • Types of Cryptography. • Types of Classical Cryptography. • Substitution Cipher. • Caesar Cipher.

4. Types of Cryptography is a type of cipher that was used historically but now has fallen. Classical Cipher:  is the cornerstone of computer and communications security. Its foundation is based on various concepts of mathematics such as number theory, and probability theory. Modern cryptography:

5. Before Computer Era • Substitution Cipher. • Caesar Cipher. • Atbash Cipher. • Transposition Cipher. • Columnar Cipher. • Route Cipher.

6. Example: Use Caesar System to Encrypt (Kurdistan) with key=3 Solution: 8 4 K U R D I S T A N 2 5 7 U X N G L V W D Q 6 3 1 9

7. Example: Use Caesar System to Decrypt (KDZOHU) with key=3 Solution: 2 5 3 K D ZOH U 1 W A H L E R 6 4

8. Conclusion Security objectives addressed by cryptography: • Confidentiality: Cryptography. • Classical Ciphers have been Fallen. • Modern Cipher is a Cornerstone of Computer Era. • Caesar Cipher: Shifting Letters.

9. References • William J. Buchanan, Cryptography, River Publishers, Denmark 2017. • Hans Delfs, Helmut Knebl, Introduction to Cryptography Principles and Applications, 3rd ed., Springer, 2016. • Wade Trappe, Lawrence Washington, Introduction to Cryptography with Coding Theory, 2nd ed., USA Pearson, 2006.

10. Home Work • Use Caesar System to Encrypt the Word “Sulaimania” with key=19? • Use Caesar System to Decrypt the Word “KZNCHVMBV” with key=5? • What is the difference between Cryptography & Cryptanalysis?

11. Next Lecture • Transposition Cipher. • Methods that Use Transposition Cipher: • Columnar Cipher. • Route Cipher.