1. Cryptography
Dr. X

2. Outline
What is cryptography?
Ceasar Cipher
Public key cryptography

3. What is cryptography?
Cryptography or cryptology (from Greek κρυπτός kryptós, "hidden, secret"; and γράφειν graphein, "writing", or -λογία -logia, "study", respectively[1]) is the practice and study of techniques for secure communication in the presence of third parties called adversaries. (from Wikipedia)
science/cryptography/crypt/v/intro-to-cryptography

4. Types of cryptography
Symmetric: encryption methods in which both the sender and receiver share the same key
Ex. Ceasar Cipher
What are the pros and cons?
Asymmetric/public key: the public key may be freely distributed, while its paired private key must remain secret. In a public-key encryption system, the public key is used for encryption, while the private or secret key is used for decryption.
Diffie-Hellman
RSA

5. Terminology
Key
Public
Private
Encryption key
Cipher
Plain text

6. One time pad
science/cryptography/crypt/v/one-time-pad
What are the pros and cons of this type of encryption?

7. Public key encryption

8. Public key encryption Choose p = 3 and q = 11
Compute n = p * q = 3 * 11 = 33
Public key is (e, n) => (7, 33)
Private key is (d, n) => (3, 33)
The encryption of m = 2 is c = 27 % 33 = 29
The decryption of c = 29 is m = 293 % 33 = 2

9. Modulo Operation % Remainder of division Ex. 5 % 4 = 1
If I was trying to divide 5 with 4, 4 can fit in 5 once and the remainder is 1
Practice:
100 % 3
35 % 4
18 % 19

10. Crypto exercise Symmetric key cryptography with Ceasar cipher
Asymmetric key crypto with RSA

11. Why do we need cryptography?
Internet is an open medium
Confidentiality
Integrity…