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BIP 54: clarify 64-byte transactions item description and rationale #2159

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BIP 54: clarify 64-byte transactions item description and rationale #2159

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346f938
bip-0054: spell out in more places that 64 bytes is for witness-strip…
darosior May 12, 2026
5c67f90
bip-0054: clarify rationale for invalidating 64-byte txs
darosior May 14, 2026
8ae3af5
bip-0054: state explicitly fake inclusion proofs only concern SPV ver…
darosior May 15, 2026
72d8275
bip-0054: less redundancy in 64-byte rationale, move caching risk to …
darosior May 15, 2026
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10 changes: 5 additions & 5 deletions bip-0054.md
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Expand Up @@ -38,10 +38,10 @@ users, increasing the cost to independently fully validate the consensus rules.
be used by miners to attack their competition, creating perverse incentives, centralization
pressures and leading to reduced network security.

In computing a block's Merkle root, a 64-byte transaction can be interpreted both as an intermediate
node in the tree and as a leaf in the tree. This makes it possible to fake inclusion proofs by
pretending a 64-byte block transaction is an inner node, as well as to pretend the inner nodes on
one level of the tree are the actual block transactions.
In computing a block's Merkle root, a transaction with exactly 64 bytes of non-witness data can be
interpreted both as an intermediate node in the tree and as a leaf in the tree. This makes it
possible to fake inclusion proofs by pretending a 64-byte block transaction is an inner node, as
well as to pretend the inner nodes on one level of the tree are the actual block transactions.
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Since [bip-0034][BIP34] activation, explicit [bip-0030][BIP30] validation is not necessary until
block height 1,983,702[^0]. Mandating new coinbase transactions be different from the early
Expand Down Expand Up @@ -146,7 +146,7 @@ Bitcoin Core version [30.0][Core 30.0] and later will not generate a block templ
transaction that violates the signature operations limit introduced in this BIP.

Bitcoin Core version [0.16.1][Core 0.16.1] and later will neither relay nor create block templates
that include 64-byte transactions.
that include transactions whose witness-stripped serialized size is exactly 64 bytes.

The coinbase transaction is usually crafted by mining pool software. To the best of the authors'
knowledge, there does not exist an open source reference broadly in use today for such software.
Expand Down