Exploring the Vigenère Cipher
From Bob Brown
This video introduces the Cæsar Cipher, explains how mono-alphabetic substitution ciphers can be cracked, and then introduces the Vigenère Cipher. There's an explanation of how to use the Vigenère tableau to implement a one-time pad, and a brief mention of the key exchange problem and of modern symmetric key ciphers.
Further reading and exercise sheets are here: https://ccse.kennesaw.edu/outreach/crypto/index.php