Bitcoin Script

1. What Is Bitcoin Script

Bitcoin Script is the stack-based, non-Turing-complete scripting language used to define the conditions under which bitcoins can be spent. It powers everything from simple single-signature payments to multisig and complex smart contracts.

2. How It Works

Every Bitcoin output is locked with a scriptPubKey (a "lock" script), and spending it requires an unlocking script (scriptSig or witness). The two scripts are executed together on a stack; if execution completes with a truthy value, the spend is valid. Script is intentionally limited — no loops or unbounded computation — to keep validation deterministic and safe.

3. Why It Matters

Bitcoin Script is why Bitcoin is more than digital cash: it enables multisig, timelocks, and second-layer systems like Lightning. Understanding Script illuminates Bitcoin's security model and its deliberate trade-off of expressiveness for safety, which contrasts with Turing-complete chains like Ethereum.

4. Key Facts

• Standard opcodes: OP_DUP, OP_HASH160, OP_EQUALVERIFY, OP_CHECKSIG
• Taproot (2021) introduced Tapscript with Schnorr signatures and MAST
• Non-Turing-complete: no loops or recursion
• Lightning Network is built on HTLCs expressed in Script

5. Related Concepts

• bitcoin
• taproot
• smart-contract
• segwit