Protocol & Consensus • Estimated 30m

64-Byte Transaction Bug

protocol.64-byte-transaction-bug

A 64-byte witness-stripped transaction can look like the preimage of an internal Merkle-tree node, creating ambiguity that can be abused against SPV proofs and other partial block verifiers. Proposed fixes such as BIP 53 and the consensus-cleanup package remove or constrain that edge case rather than relying on every verifier to defend against it separately.

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Curated resources (4)

• BIP 53: Disallow 64-byte Transactions (article) Primary proposal describing the Merkle ambiguity and SPV-proof attack surface created by 64-byte witness-stripped transactions.
• Bitcoin Optech Topic: Merkle Tree Vulnerabilities (article) Canonical overview of why internal-node ambiguity matters and how 64-byte transactions fit into the mitigation debate.
• Bitcoin Optech Topic: Consensus Cleanup Soft Fork (article) Tracks the broader cleanup proposal that includes invalidating future 64-byte transactions.
• Mastering Bitcoin (book) Broad reference for transactions, block commitments, and SPV assumptions needed to understand the bug.

Direct prerequisites (1)

• Block Structure

Direct dependents (0)

• None

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