It's a weird fact about, I suppose, mathematics, that you can create a basically-unforgeable identity and exchange secrets using simple maths which fit onto less than a page (asymmetric cryptography - DSA, RSA, Diffie-Hellman), and even fit public keys into 32 bytes (X25519/Ed25519) with more complexity - unless decently big quantum computers are practical, in which case one of the two useful algorithms they can run breaks everything and you have to move to much scarier maths and put up with much larger signatures and keys.