Fundamentals for Blockchain

• public key cryptography, assymetric cryptography
• hash functions
• digital signatures
• public key infrastructure

Hash functions in this context are functions that for any given key produce a unique output of a determined length for any input length.

Bob, Alice, and Chris are all on a network and want to communicate. How can Alice send Bob a message such that only Bob can read it, and Bob can be sure it came from Alice?

m = encrypt_with_bob_public_key(encrypt_with_alice_private_key(hash(msg)) + msg)

Bob decrypts m with his private key and validates signature with alice's public key.

How can Bob be sure Alice's public key really came from Alice? It is digitally signed by a trusted Certificate Authority, of which Bob already has the public key.