consensus

Part 5 of the beginner guide. Two simple rules — everyone checks the rules, and the chain with the most work wins — are what keep a system with no boss honest.

Part 2 of 5. Thousands of computers end up agreeing on the exact same record by checking each other's work and chaining every page to the one before it.

Forensicxs published a line-by-line walkthrough of Bitcoin v0.1's 31,794 lines of source code, covering all 31 files.

Proof of work vs proof of stake, scored axis by axis with dated numbers: market cap, track record, energy, attack cost, decentralization, speed and new-chain adoption, with DPoS and PoA beside them.

Specifies a version-bits soft fork activation mechanism using block heights instead of timestamps, adding a flag that can guarantee lock-in before a timeout height.

On January 15, 2016, Bitcoin Core v0.12 replaced OpenSSL with libsecp256k1 — Wuille and Maxwell's custom elliptic-curve library — for consensus-critical ECDSA verification.

Defines the original version-bits mechanism for signaling and activating soft forks in parallel via the block nVersion field, using median-time-past thresholds and a fixed timeout.

Soft fork redefining lock-time eligibility to use the median of the past 11 blocks' timestamps instead of a single block's timestamp, removing miners' incentive to lie about block time.

Repurposes the transaction sequence number as a consensus-enforced relative lock-time, letting an input stay unspendable for a set number of blocks or time after its output confirms.

Restricts ECDSA signatures in Bitcoin scripts to strict DER encoding, removing OpenSSL's implicit role in consensus validity and reducing transaction malleability.

Defines OP_CHECKLOCKTIMEVERIFY, a soft-fork opcode that makes a transaction output unspendable until a specified block height or time, enabling escrow and time-locked contracts.

Embeds the block height in each coinbase transaction's scriptSig and raises block version to 2, activated once 95% of the last 1,000 blocks signal support, enforcing coinbase uniqueness.

On November 20, 2011, Bitcoin v0.5 shipped with the Crypto++ SHA-256 subset removed and replaced by OpenSSL. Wei Dai's library, a direct codebase dependency since v0.1, was gone.

Satoshi's standalone bitcoin.org explanation of the Byzantine Generals problem, using a proof-of-work chain to make the generals agree on a plan.

A source-level map of Bitcoin v0.1: the byte boundaries for transaction, block, and signature hashes, and the reuse of one serializer across network and disk paths.

How Bitcoin nodes agree on a single chain: SHA-256d proof of work, the difficulty adjustment algorithm, block validation rules, fork resolution, and probabilistic finality.

Bitcoin's threat model mapped end-to-end: what the protocol trusts, what it defends against, how each attack is countered, and where open risks remain.

Donald gave the difficulty its 1982 name; Satoshi claimed a solution outright, swapping the fixed world of known generals for an open one. The King's wi-fi answer became a page on bitcoin.org.