How Blockchains Work by Hand: Ledgers, Toy Hashes & Chained Blocks, Merkle Trees, Proof-of-Work Targets, Difficulty Adjustment, Unspent Outputs & Fee Markets

What you'll build

What you will be able to do

Each lab ends with a concrete result that you build yourself and the checker confirms, cell by cell.

• Turn a log of ten transfers into received, sent and final balances with SUMIFS, then replay the log in order with growing ranges and flag the transfer where Ana spends points she does not have yet.
• Recompute a toy hash for each of eight blocks from its data and stored previous hash, compare it with the stored hash, check every link to the previous block and find the first block someone edited.
• Build a Merkle tree over six transaction hashes, pair the odd node with itself, compute the root and walk a three-step proof that Tx 5 is in the block without looking at the other transactions.
• Test twenty given nonce hashes against a target, find the first valid nonce with MINIFS, calculate the chance that a single try succeeds and the expected number of tries.
• Add up the block times of a twelve-block window, compare them with the target, clamp the adjustment factor between 0.8 and 1.25 and set the new difficulty and target.
• Add up Mia's unspent outputs, look up the two outputs she spends, send the change back to her and find the fee hidden in a transaction where the change was forgotten.
• Turn fees into fee rates, rank twelve waiting transactions, fill a 1,000-unit block from the top of the ranking and estimate in which block a low-fee transaction will finally be included.
• Model Ledgerwood's issuance schedule with POWER and INT, add up the supply towards its limit, compare the reward value per block with a fictional energy cost and chart both lines.