http://ciphersbyritter.com/ - Best cryptography resource out there, by a mile. Explains the basics thoroughly and in a way that’s easy to understand. Debunks myths and covers stuff that other sites don’t dare to touch. Clearly, the author has a deep understanding of the topic.
https://www.cryptomuseum.com/index.htm
https://cryptographyacademy.com/rsa/
https://signal.org/docs/specifications/doubleratchet/
https://www.bunniestudios.com/blog/?p=6140
https://andrea.corbellini.name/2015/05/17/elliptic-curve-cryptography-a-gentle-introduction/