http://ssd.iykpqm7jiradoeezzkhj7c4b33g4hbgfwelht2evxxeicbpjy44c7ead.onion/ps/module/deep-dive-end-end-encryption-how-do-public-key-encryption-systems-work
RSA is often used to generate key pairs for PGP-encrypted emails. The public key and private key are generated and tied together. Both rely on the same secret prime numbers. The private key represents two secret prime numbers. Metaphorically, the public key is the product number: it is made up of the same two very large prime numbers used to make the private key.