Coincidentally I'm also reading about Lamport signature (https://blog.cryptographyengineering.com/2018/04/07/hash-based-signatures-an-illustrated-primer/ https:

Coincidentally I'm also reading about Lamport signature (https://blog.cryptographyengineering.com/2018/04/07/hash-based-signatures-an-illustrated-primer/ https://blog.cryptographyengineering.com/2018/04/07/hash-bas...). It's really interesting because it only uses hash function and doesn't rely on trapdoor function! I think quite many people (me included) only learn about digital signature after public key cryptography, so it's quite a surprise to know about Lamport signature. Also, IIUC, because it doesn't rely on trapdoor function it also resistant against quantum computer in the future