The document discusses different methods for securing blockchains known as consensus algorithms. It explains proof of work, which uses externally produced results like CPU mining to validate blocks, and proof of stake, which uses internally produced results like the amount of coins held. Proof of stake calculates a score based on coin amounts to determine the authoritative chain in a fork. The document provides examples of other consensus algorithms like proof of activity, proof of elapsed time, and compares the main differences between proofs that use external versus internal results.