Bitcoin: Witness hash mismatch error when sending signed transaction to Regtest
As a Bitcoin developer, you’re probably no stranger to the nuances of running a testnet node or testing your own wallet. However, when it comes to sending transactions, even simple operations can throw up unexpected errors. In this article, we’ll take a look at a specific error that’s causing frustration for many users and explore why it occurs.
The Error: Witness Program Hash Mismatch Error
When you try to send a transaction to your Bitcoin regtest node (also known as a “mock” or “testnet” node), the error message displayed is quite informative:
Status Err("RPC error: Object {\"code\": Number(-26), \"message\": Invalid hash for witness program"
At first glance, this seems to be an error related to the transaction itself. However, upon closer inspection, we can see that the actual problem lies with the Witness program.
The Witness Program: A Cryptographic Hashing Scheme
In Bitcoin, transactions are represented as a sequence of blocks with various elements such as inputs, outputs, and transactions. To secure these transactions, each block is linked to its predecessor via the Mordell-Samuel curve, a cryptographic hash function that verifies the chain of ownership.
The Witness Program is responsible for generating this cryptographic hash, which is essential to ensure the integrity of the blockchain. It is essentially a complex mathematical formula that takes into account various parameters, such as the block number, the Merkle root, and witness data (e.g., transaction input indices and outputs).
Hash Mismatch Error: What’s Wrong
When you send transactions to your regtest node, you probably use the regtest command-line tool to broadcast your transactions. However, in some cases, this process can result in a hash mismatch error.
Here’s what happens:
- Witness program hash calculation: When you execute a transaction on your regtest node, the witness program is used to generate a cryptographic hash for each block.
- Transaction Validation: You then verify that the transaction was validated correctly using tools such as
bfs(Bitcoin Fork Checker) orbfs-checker.
- Hash Calculation: Before sending the transaction to the network, you calculate the hash of the witness program using a tool such as
witnessprogramhash.
The Problem: Invalid Witness Program Hash
In some cases, there may be an issue with calculating the witness program hash. This can happen for a variety of reasons, such as:
- Incorrect input data (e.g., invalid transaction input indices or outputs).
- Outdated witness program versions.
- Network connectivity issues.
When your regtest node encounters a hash mismatch error, it is usually caused by one of these factors. In this case, the ‘regtest’ tool displays an error message stating that the witness program hash is invalid.
Solution: Debugging and Troubleshooting
To resolve this issue, follow these steps:
- Check Input Data: Make sure all input data is correct and valid.
- Update Witness Program
: Check for updates to the witness program code or versions.
- Rerun
witnessprogramhash: Use a tool likewitnessprogramhashwith the correct inputs to generate the witness program hash again.
If none of these steps resolve the issue, you may need to seek further assistance from the Bitcoin community or your testnet node admin.
Conclusion
The Witness program hash mismatch error is a common issue that can be caused by a variety of factors. By understanding the underlying causes and taking corrective action, you should be able to resolve this error and successfully send transactions to your regtest node. Remember to verify input data, update Witness program versions, and rerun witnessprogramhash with the correct inputs to ensure a smooth transaction experience.
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