Lecture No. 5: Data Encryption Dr. Mazin Alkathiri from Seiyun University's Department of Information Technology discussed data encryption. There are two main types of encryption - symmetric key which uses the same key for encryption and decryption, and public key which uses a pair of linked keys, one public and one private. Encryption transforms plaintext into unreadable ciphertext, while hashing generates unpredictable values to verify message integrity during transmission. Digital signatures authenticate senders and ensure message integrity through certificates issued by authentication authorities. Firewalls control network traffic between local and external networks to minimize security risks.