2. What is Encryption? - The translation of data into a secret code - To read an encrypted file, you must have access to a secret key or password that enables you to decrypt it - Unencrypted data is called plain text - encrypted data is referred to as cipher text

3. Dear students, My phone no. Is 24750331 Ghdu vwxghqwv, Pb skrqh qr. Lv 57083664 Dear students, My phone no. Is 24750331 Encrypt Decrypt Plain textCipher text Plain text

4. Activity Fgct encuu yg ctg iqkpi vq vcnm cdqwv fcvc gpetarvkqp Encrypted text: Original text:

5. Common algorithms of Encryption Symmetric Encryption Asymmetric Encryption

6. Symmetric Encryption A type of encryption where the same key is used to encrypt and decrypt the message

7. Symmetric Encryption (Example) Plain text1 0 1 1 0 1 1 0 Key1 1 0 1 1 1 1 0XOR Cipher text0 1 1 0 1 0 0 1 Key1 1 0 1 1 1 1 0XOR Plain text1 0 1 1 0 1 1 0 Encrypt Decrypt Same Key

8. Asymmetric Encryption Asymmetric encryption (also called public-key encryption) involves a pair of keys - a public and a private key. The public key is published in a public directory and the corresponding private key is kept secret.

9. Asymmetric Encryption The sender of the data encrypts the data with the public key of the receiver The data can be decrypted only with the private key of the receiver

10. Asymmetric Encryption Plain Text Plain Text Cipher Text

11. How to use two different keys? One key is the inverse of the other: Public key = 3, Private key = 1/3 Plain text = 4 Encryption: cipher text = public key * plain text = 3 * 4 = 12 Decryption: plain text = private key * cipher text = 1/3 * 12 = 4

12. Discussion What are the uses of encryption?

13. Activity Construct a simple algorithm of encryption.