Version

An introduction to the Bitcoin transaction version number field.

What is a Transaction Version Number?

The transaction version number is a field in the Bitcoin transaction data structure that indicates the version of the transaction format and rules. It defines the structure of the transaction and supports protocol upgrades and the introduction of new features.

Purpose of the Version Number

1. Define Transaction Format

The version number indicates the format and interpretation of the transaction. Different versions of transactions may vary in inputs, outputs, or script syntax. Miners and nodes parse and validate transactions based on the version number.

2. Support Protocol Upgrades

The version number allows the Bitcoin protocol to gradually introduce new features and improvements. For example, Segregated Witness (SegWit) was implemented by increasing the version number. Older nodes can continue to process transactions in the old format, while newer nodes can understand and process transactions in the new format.

3. Backward Compatibility

The version number allows new features to be introduced without breaking old features or transactions. Nodes can selectively process transactions based on the version number, ensuring backward compatibility.

Values of the Version Number

The Bitcoin transaction version number is a 4-byte integer. The main version numbers currently in use include:

  • Version 1: The original transaction version, used since the inception of Bitcoin.

  • Version 2: Introduced CHECKSEQUENCEVERIFY (BIP 68 and BIP 112), supporting relative time locks.

  • Version 10: Used in the MVC network, supporting MetaTxid calculation.

Retrieving the Transaction Version Number

Using the Bitcoin Core client, you can obtain detailed transaction information, including the version number, through the command line interface (CLI).

Retrieving Transaction Details

mvc-cli getrawtransaction <txid> 1

The JSON data returned by this command includes the transaction's version number.

Example

Suppose we have a transaction with the transaction ID <txid>. Using the command above to retrieve its details, we get the following result:

{
  "txid": "<txid>",
  "version": 2,
  "locktime": 0,
  "vin": [
    ...
  ],
  "vout": [
    ...
  ]
}

In this example, the "version" field is 2, indicating that the transaction uses version 2 format and rules.

Evolution of the Version Number

The evolution of Bitcoin transaction version numbers reflects the gradual improvements and expansions of the protocol. For example, BIP 68 and BIP 112 introduced relative time lock functionality and were implemented by increasing the version number. Future protocol upgrades may further increase the version number, introducing more new features and improvements.

In the MVC network, version number 10 is used to support MetaTxid calculation, providing new functionality for transaction verification and processing.

Summary

The transaction version number is a crucial field in the Bitcoin transaction data structure, used to define the transaction format and support protocol upgrades. Through the evolution of the version number, the Bitcoin protocol can gradually introduce new features while maintaining backward compatibility. Understanding the role and retrieval methods of the transaction version number helps to gain a deeper understanding of the structure of Bitcoin transactions and the evolution of the protocol.

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