Genesis upgrade

The upgrade restored many aspects of the Bitcoin protocol that had been modified in previous software updates including the removal of most limit based consensus rules, replacing them with miner configurable settings that give node operators the autonomy needed to set their own limits as they determine are practical.

The upgrade was locked in when this transaction was mined at block height 620539. The transaction uses a script that would previously have been considered to violate the protocol rules and rejected by network nodes running the BitcoinSV node client.

Further details on the changes made in the upgrade can be found here and the full specification is available here.

Block Consensus Rules

These consensus rules apply to blocks that are produced after Genesis activation.

• Block Size – The consensus rule that restricts the maximum size of a block to a specific number of bytes has been converted into a configurable consensus rule. The size of a block is the size in bytes of the serialized form of the block including the block header and all of the transactions confirmed by the block. MINERS ARE EXPECTED TO REACH CONSENSUS ON THIS VALUE AND CONFIGURE IT MANUALLY.

• Number of CheckSig Operations per MB of Block Space – The consensus rule that limits the number of checksig operations per megabyte of block space has been removed.

Transaction Consensus Rules

These consensus rules apply to transactions that are confirmed in blocks after Genesis activation.

• Maximum Transaction Size – The size of a transaction is the size in bytes of the serialized form of the transaction. The maximum size of a transaction is 1GB (1,000,000,000 bytes). This limitation is expected to be lifted in the future.

• Maximum Number of CheckSig Operations per Transaction – The consensus rule that limits the number of checksig operations per transaction has been removed.

• nLockTime and nSequence – After Genesis activation, the functionality of the nLockTime field of a transaction and the nSequence fields of transaction inputs revert to their original purpose. The rules defined here only apply to transactions that are confirmed after Genesis activation.

Script Language Rules

This section contains changes to the Script Language Rules. Bitcoin Script is the programming language that is used to lock and unlock transaction outputs. More can be found at: Advanced Bitcoin Scripting. The rules defined here apply to locking and unlocking scripts for transaction outputs that are created after the Genesis activation. The previous rules apply to transaction outputs created prior to Genesis activation.

OP_RETURN Functionality

The functionality of the OP_RETURN operation is being restored. OP_RETURN will cause termination of the script and the validity of the script is determined by the value of the top item on the stack. See OP_RETURN.

Data Types

All data items in Bitcoin Script as a byte sequence. Some operations interpret their parameters as numeric or boolean values and require the itme to fulfill the requirements of those types. Some operations produce items on the stack which are valid numeric or boolean values.

Bitcoin Script Formal Grammar

A formal grammar has been defined for Bitcoin Script. More can be found at: Opcodes used in Bitcoin Scripting.

• Validity of Script Consensus Rule – The locking and unlocking scripts for every input of a transaction must be grammatically valid, as defined by the formal grammar above.

• PUSHDATA Only in Unlocking Script Consensus Rule – After Genesis activation, the unlocking scripts used in transaction inputs may only contain PUSHDATA operations, as defined by the formal grammar. In contrast to all the other updates in this section, this consensus rule is activated for all inputs of transactions that are, or will be, confirmed in a block after Genesis activation, regardless of the height of the UTXO being spent. This rule is a subset of the Validity of Script Consensus Rule defined above but is included separately because the activation conditions are different.

Consensus Rule Replacement

Functionality provided by these consensus rules is now covered by the Stack Memory Usage Consensus Rule.

Consensus Rule	Description
Script Element Size	Limits the maximum size of a script element.
Stack Size	Limits the combined number of elements that can be placed on the stack and the altstack.
Script Size*	The maximum size of the script
Number of Non-Push Operations per Script	Limits the number of non-push operations per script. Other capabilities manage the cost of execution.

• functionality also covered by the Maximum Transaction Size Consensus Rule.

Consensus Rule Changes

Consensus Rule	Description
Numeric Value Size	For a byte sequence to represent validly a numeric value, the length of the byte sequence must be less than or equal to 750,000 bytes. A byte sequence that is larger than this is a valid byte sequence but is not a valid numeric value.
Number of Public Keys per Multisig Consensus Rule	Limits the number of public keys per multisig has been changed to be 2^31-1 (INT32_MAX).
Stack Memory Usage	Limits the amount of memory that can be used on the stacks. This rule is evaluated against the sum of the memory used by the stack and the memory used by the altstack.

Sunsetting

• P2SH, OP_CHECKLOCKTIMEVERIFY, and OP_CHECKSEQUENCEVERIFY – The P2SH capability is being removed by the Genesis upgrade and the presence of a p2sh script template in an output will invalidate a transction. The opocde operations revert to NOPs, which have no effect.

• Disabling Operations Consensus Rule – OP_2MUL, OP_2DIV, OP_VERIF, OP_VERNOTIF. If they are present in un-executed script, the script execution may succeed.

Standard Local Policies

Policies are settings that are configured by software operators. These settings are generally required by software implementations.

Policies control which transactions the software will propagate across the P2P network or include in a block. However, policies are not Bitcoin Rules or Consensus Rules and are not used to determine the validity of blocks or the transactions confirmed by the block.

Standard Local Transaction Policies

• Maximum Acceptable Transaction Size Policy – The maximum acceptable transaction size is a standard policy that configures the largest transactions that the software will propagate across the P2P network or include in a block.
• Transaction Evaluation Timeout – The transaction evaluation timeout is a standard policy that defines the maximum amount of time that the software will allow for the evaluation of transaction before terminating the evaluation and rejecting the transaction. This setting is always defined with a time unit and the default value 1 second.

Standard Local Script Language Policies

• Numeric Value Length – the length of numeric value policy defines the maximum length of a byte sequence to be considered a valid numeric value. The default value for this value is 250,000 bytes.
• Stack Memory Usage – The stack memory usage policy limits the amount of memory that can be used on the stacks. This policy is evaluated against the sum of memory used by the stack and the memory used the altstack.

Standard Local P2P Network Policies

• Propagation of non-Standard Transactions – After Genesis activation, the default setting for this policy is that non-standard transactions will be propagated across the P2P network. Before Genesis activation, the default setting for this policy was non-standard transactions are not propagated the P2P Network. Policies such as Maximum Acceptable Transaction Size Policy still apply.