Blockchain technology relies heavily on understanding public and private keys. How they are generated and used. This OpenSSL Cookbook is a good reference.
I found the first half more informative and useful than the second half. Here is the link to the online version: https://www.feistyduck.com/library/openssl%2dcookbook/online/
For other formats, check out: https://www.feistyduck.com/library/openssl-cookbook/