A coin is a shared ledger
Start designing DCoin by separating the problems of ownership, communication and agreement. Peer-to-peer networks, hashes and signatures each solve a different part.
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DCoin: from a ledger to a blockchain
Design a small cryptocurrency, then follow Bitcoin from signed transactions to the bytes stored on disk and exchanged between peers.
What would it take to build a currency whose ledger nobody owns?
DCoin is a thought experiment for answering that question one decision at a time. We start with a shared record of payments, introduce the cryptography that makes those payments verifiable, and work through the harder problem of choosing a history when participants disagree. Then we leave the toy design behind and read actual Bitcoin block and network data.
The five parts connect the model to the implementation: peer-to-peer networks and signatures; transactions and hash-linked blocks; consensus and incentives; a block decoded byte by byte; and the messages that carry it across a network. The illustrations combine TikZ with SVG artwork; the practical chapters include real terminal and Wireshark captures. The binary examples include small Python programs you can run without a Bitcoin node.
No trading, price predictions or token launch. Just the engineering of a ledger that has to survive disagreement.
Chapters
From signed payments to blocks
Model a DCoin payment, follow its inputs and change, then connect transactions to a block header through a Merkle tree.
Which history counts?
Forks are normal. Learn how proof of work compares competing histories, where its security assumptions enter, and how rewards connect the ledger to its operators.
Reading a Bitcoin block, byte by byte
Decode a historical block header and its first transaction. Follow file offsets, byte order, proof of work and a 50.05877600 BTC coinbase output with runnable Python.
Reading Bitcoin's network traffic
Follow a Bitcoin message from a TCP stream to its payload. Decode verack, inspect a block response and distinguish what a packet capture proves from what it merely suggests.