A secondary merkle root MUST be calculated as per BIP 's commitment structure specification to be inserted into the generation (coinbase) transaction. Servers MUST NOT include a commitment in the "coinbasetxn" key on the template. Clients MUST insert the commitment as an additional output at the end of the final generation (coinbase. The Foundation has an organizational structure designed to link pioneers in the bitcoin blockchain space and related industries, with a commitment to empowering local communities across the world. Contribute to bitcoin/bitcoin development by creating an account on GitHub. Commitment structure and deployment Includes a fix by Suhas Daftuar and LongShao /* * Produce the necessary coinbase commitment for a block (modifies the hash, don't call for mined blocks). */.
Bitcoin commitment structureBIP - Bitcoin Wiki
Probably not an issue in the current way we use the commitment, but could be in the future. Anyway, what specific use cases do you think a 1MB worst case, and few KB average case, proof size hold back in the next year or two? It is also possible to add an additional commitment location for the same data in a future softfork that is more proof-compatible, if wanted.
Skip to content. New issue. Jump to bottom. Labels Brainstorming Consensus. Copy link Quote reply. Copy link. Contributor Author. Namecoin should not use the segwit nonce at all. It is reserved for future consensus-critical extensions. If they or anyone else creating a non-consensus critical commitment need a guarantee that the commitment is unique, they should pick a place that has that property.
Including adding their own last-position coinbase output. MarcoFalke added Consensus Brainstorming labels Jul 6, Pick any other example, focusing on namecoin is a red herring.
TXO commitments. You could commit to two different TXO structures. No, you cannot. Only the last commitment matters for consensus. Yes, that means validation needs to see the full coinbase transaction, which they already do anyway. Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment. Brainstorming Consensus. Linked pull requests. You signed in with another tab or window.
Reload to refresh your session. You signed out in another tab or window. Definition of txid remains unchanged: the double SHA of the traditional serialization format:. A new wtxid is defined: the double SHA of the new serialization with witness data:.
Format of nVersion , txins , txouts , and nLockTime are same as traditional serialization. The flag MUST be a 1-byte non-zero value. Currently, 0x01 MUST be used. The witness is a serialization of all witness data of the transaction. Each txin is associated with a witness field. Witness data is NOT script.
A non-witness program defined hereinafter txin MUST be associated with an empty witness field, represented by a 0x If all txins are not witness program, a transaction's wtxid is equal to its txid.
A new block rule is added which requires a commitment to the wtxid. The wtxid of coinbase transaction is assumed to be 0x A witness root hash is calculated with all those wtxid as leaves, in a way similar to the hashMerkleRoot in the block header. The commitment is recorded in a scriptPubKey of the coinbase transaction. It must be at least 38 bytes, with the first 6-byte of 0x6a24aa21a9ed , that is:. If there are more than one scriptPubKey matching the pattern, the one with highest output index is assumed to be the commitment.
The value of the first push is called the "version byte". The following byte vector pushed is called the "witness program".
There are two cases in which witness validation logic are triggered. Each case determines the location of the witness version byte and program, as well as the form of the scriptSig:. If the version byte is 0, but the witness program is neither 20 nor 32 bytes, the script must fail. If the version byte is 1 to 16, no further interpretation of the witness program or witness stack happens, and there is no size restriction for the witness stack. These versions are reserved for future extensions. Blocks are currently limited to 1,, bytes 1MB total size.
We change this restriction as follows:. Base size is the block size in bytes with the original transaction serialization without any witness-related data, as seen by a non-upgraded node. Total size is the block size in bytes with transactions serialized as described in BIP , including base data and witness data.
Sigops in the current pubkey script, signature script, and P2SH check script are counted at 4 times their previous value. This rule applies to both native witness program and P2SH witness program. The following definitions are not used for consensus limits, but are suggested to provide language consistent with the terminology introduced above.
Base transaction size is the size of the transaction serialised with the witness data stripped. Total transaction size is the transaction size in bytes serialized as described in BIP , including base data and witness data. Before large-scale deployment in the production network, developers should test the scripts on testnet with the default relay policy turned on, and with a small amount of money after BIP is activated on mainnet.
A major difference at consensus level is described in BIP , as a new transaction digest algorithm for signature verification in version 0 witness program. Three relay and mining policies are also included in the first release of segregated witness at reference implementation version 0.
Softforks based on these policies are likely to be proposed in the near future. To avoid indefinite delay in transaction confirmation and permanent fund loss in a potential softfork, users MUST observe the new semantics carefully:.
The '0' in scriptPubKey indicates the following push is a version 0 witness program. The witness must consist of exactly 2 items. The HASH of the pubkey in witness must match the witness program. Comparing with the previous example, the scriptPubKey is 1 byte bigger and the scriptSig is 23 bytes bigger.
Although a nested witness program is less efficient, its payment address is fully transparent and backward compatible for all Bitcoin reference client since version 0.
The length of the witness program indicates that it is a P2WSH type. The last item in the witness the "witnessScript" is popped off, hashed with SHA, compared against the byte-hash in scriptPubKey, and deserialized:. The increased size improves security against possible collision attacks, as 2 80 work is not infeasible anymore By the end of , 2 84 hashes have been calculated in Bitcoin mining since the creation of Bitcoin.
Comparing with the previous example, the scriptPubKey is 11 bytes smaller with reduced security while witness is the same. However, it also requires 35 bytes in scriptSig. The new commitment in coinbase transaction is a hash of the witness root hash and a witness reserved value.
The witness reserved value currently has no consensus meaning, but in the future allows new commitment values for future softforks. For example, if a new consensus-critical commitment is required in the future, the commitment in coinbase becomes:.
For backward compatibility, the Hash new commitment witness reserved value will go to the coinbase witness, and the witness reserved value will be recorded in another location specified by the future softfork.
Any number of new commitment could be added in this way. Any commitments that are not consensus-critical to Bitcoin, such as merge-mining, MUST NOT use the witness reserved value to preserve the ability to do upgrades of the Bitcoin consensus protocol.
The optional data space following the commitment also leaves room for metadata of future softforks, and MUST NOT be used for other purpose.