1. Information Security CPIT 425 Instructor: Bashair Alrashed LAB1

2.  Discussed the Basics of encryption and decryption techniques  know there are many algorithms for encryption and decryption  Students will be divided into groups of 3 girls  Understand how additive (Caesar) encryption and decryption works  should implement the algorithm using a suitable programming language. OUTLINES:

3.  know the importance of encryption and decryption techniques  Learn how to encrypt a plaintext using (Caesar) algorithm. OUTCOMES:

4. TRADITIONAL SYMMETRIC ‐ KEY CIPHERS:

5.  Plaintext is read by the user, he wants to encrypt it in some manner. The hacker tries to decrypt the cipher text using different keys.  The hacker only sees the cipher text, he didn’t know the key and way in which the plain text is encrypted.  Encryption and decryption algorithms depend on the key itself. TRADITIONAL SYMMETRIC ‐ KEY CIPHERS:

6.  A substitution cipher replaces one symbol with another. Substitution ciphers can be categorized as either monoalphabetic ciphers or polyalphabetic ciphers.  In monoalphabetic substitution, the relationship between a symbol in the plaintext to a symbol in the cipher text is always one-to-one SUBSTITUTION CIPHERS

7.  mathematical nature. ALGORITHM 1: ADDITIVE CIPHER (CAESAR CIPHER)

8.  When the cipher is additive, the plaintext, cipher text, and key are integers in Z26. ALGORITHM 1: ADDITIVE CIPHER (CAESAR CIPHER)

9.  Example: Use the additive cipher with key = 15 to encrypt the message “hello”.  Quiz: Use the additive cipher with key = 15 to decrypt the message “WTAAD”. ALGORITHM 1: ADDITIVE CIPHER (CAESAR CIPHER)

10. -Read Plaintext (pt) -Enter key 0<Key≤ 25 -Encrypt (pt) -Show the cipher text (cp) -Decrypt cp -Show the original plain text ADDITIVE CIPHER (CAESAR CIPHER) ALGORITHM Encryption Method: For( int i=0; i < pt.length; i++) { Int emp= convert_to_number(pt,i); Int c= (temp + k ) mod 26; ct+= convert_to_letter(c); }

11.  Your program after implementing the above algorithm should be similar to the following program: ALGORITHM 1: ADDITIVE CIPHER (CAESAR CIPHER)

12. Implement (Caesar) algorithm using a suitable programming language. Note: The expected time to finish submitting next lab HOME WORK 1