Thanks everyone for the comments. Sjors, transactions are serialized in modern blocks as described by Murch.
Murch, for the purpose of computing the Merkle root transactions are serialized without witness data. Best, Antoine On Wednesday, January 14th, 2026 at 5:23 AM, Sjors Provoost <[email protected]> wrote: > > > Hi Murch, > > You're referring to the "serialization with witness data" defined in BIP 141. > > But that's not how the transaction is serialised in a block, since the > witness is > segregated. > > > The witness is committed in a tree that is nested into the block's existing > > merkle root via the coinbase transaction for the purpose of making this BIP > soft fork compatible. A future hard fork can place this tree in its own > branch. > > As long as the miner doesn't touch the SegWit OP_RETURN , which also commits > to the coinbase witness, it can safely use the legacy transaction > serialisation. > > - Sjors > > [0] > https://github.com/bitcoin/bips/blob/master/bip-0141.mediawiki#transaction-id > > > Op 14 jan 2026, om 01:23 heeft Murch [email protected] het volgende > > geschreven: > > > > Hi Sjors, > > > > On 2026-01-08 00:30, Sjors Provoost wrote: > > > > > The approach suggested by Towns [4] of appending a 0-sat OP_RETURN output > > > with > > > padding so a 4-byte nonce lands in the final 64-byte SHA256 chunk is > > > probably > > > better, but not because like nLockTime it has a small hashing midstate > > > benefit. It's easier to implement. > > > I can’t access Delving right now to read AJ’s comment, but a small nit on > > > the idea of using an additional output: BIP 141 requires coinbase > > > transaction inputs to have a 32-byte witness. Since the witness section > > > follows the outputs in the serialization, the bytes before the > > > `nLocktime` in a coinbase transaction are the witness of the coinbase > > > input, not the last output script. > > > > -Murch > > > -- > You received this message because you are subscribed to the Google Groups > "Bitcoin Development Mailing List" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To view this discussion visit > https://groups.google.com/d/msgid/bitcoindev/1B807731-DC2A-4E59-B462-5C210EF1FB73%40sprovoost.nl. -- You received this message because you are subscribed to the Google Groups "Bitcoin Development Mailing List" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion visit https://groups.google.com/d/msgid/bitcoindev/_C0iWeaJ-v24dZgcdCnKZKEgK9E493DmpG_-wD1NZnOAuECi97dZpVLuZxkONIfZjTe7km_TWFdSFfmSzVWfJ5Lkz6JTc8JwDOTg9XAInVo%3D%40protonmail.com.
