Bitcoin Script & UTXO Signature Verification

Bitcoin uses Unspent Transaction Outputs (UTXOs). Each UTXO is a coin with a locking script (scriptPubKey). To spend it, the spender provides an unlocking script (scriptSig) that satisfies the locking script. UTXOs are atomic — spent or unspent, never partial.

Bitcoin Script is a stack-based, non-Turing-complete language. Scripts execute by pushing data and running opcodes. No loops, no recursion — scripts always terminate. This intentional limitation prevents denial-of-service and makes script verification O(n) in script length.