Protocol & Consensus • Estimated 35m

Duplicate Transaction Bug

protocol.duplicate-transaction-bug

Early Bitcoin allowed some coinbase transactions to be duplicated with identical txids, which could confuse UTXO references that assumed every prior transaction id was unique. BIP 30 blocked most duplicates, BIP 34 enforced unique coinbase heights, and later cleanup proposals remove the remaining special-case burden.

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Curated resources (4)

• Bitcoin Optech Topic: Duplicate Transactions (article) Canonical overview of why identical txids were dangerous and how Bitcoin constrained them over time.
• BIP 30: Duplicate Transactions (article) Consensus rule that disallows most duplicate transactions whose outputs are not all spent.
• BIP 34: Height in Coinbase (article) Coinbase-height commitment that makes future coinbase transactions unique and closes the main replay vector.
• Mastering Bitcoin (book) Broad transaction and UTXO reference for understanding txids, coinbase structure, and consensus uniqueness assumptions.

Direct prerequisites (2)

• Coinbase Transaction
• UTXO Model

Direct dependents (0)

• None

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