Symmetric Cryptography: One-Time Pad

This lecture introduces symmetric cryptography, focusing on the one-time pad encryption method. The one-time pad requires a single key exchanged securely between partners in advance. It ensures perfect confidentiality by using keys at least as long as the messages and with higher entropy. The lecture explains how the one-time pad works through examples of message encryption and decryption, emphasizing the importance of key randomness and independence from the message. It also covers the concept of perfect confidentiality in crypto-systems, where the key's entropy must be greater than or equal to that of the messages.