Inside the Hemi Bitcoin Kit

The Hemi Bitcoin Kit (hBK) is a powerful tool designed for developers looking to create Bitcoin-aware decentralized applications (dApps) on the Hemi blockchain. The hBK offers an abstraction layer that simplifies the process of interacting with Bitcoin’s blockchain directly from the Hemi Virtual Machine (hVM), which embeds a full, indexed Bitcoin node within an Ethereum-like environment.

This guide will walk you through how to use the Hemi Bitcoin Kit to retrieve Bitcoin data, explain the key features of hBK, and explore its use cases.

Overview of the Hemi Bitcoin Kit

The hBK is a set of smart contracts that bridges Bitcoin and Ethereum, enabling developers to interact with Bitcoin data as easily as with Ethereum assets. The core idea behind hBK is to abstract away the complexities of low-level Bitcoin-Ethereum interoperability, offering developers a simple interface to access critical Bitcoin information such as balances, Unspent Transaction Outputs (UTXOs), transaction details, and block headers.

At the core of hBK’s functionality is the hVM, which embeds a fully synchronized Bitcoin node into the Ethereum Virtual Machine (EVM). This allows dApps to access real-time Bitcoin data through precompiled contracts, without relying on third-party relayers or validators. The latest release of hBK is available on the Hemi testnet.

Key Features of the Hemi Bitcoin Kit

The hBK provides several utilities for interacting with Bitcoin data directly from smart contracts, leveraging precompiled contracts for efficient and trustless queries. Here are the key features you’ll interact with when using hBK:

• Bitcoin Address Balances: Retrieve the Bitcoin balance of any address in satoshis using a smart contract call.
• UTXO Set: Access a list of unspent transaction outputs (UTXOs) for a given Bitcoin address.
• Transaction Details: Query transaction details such as inputs, outputs, and confirmations using the transaction ID.
• Block Headers: Retrieve the latest or a specific Bitcoin block header based on height.

These features allow developers to create Bitcoin-aware applications without the complexity of manually interacting with Bitcoin’s blockchain.

Struct Definitions in hBK

To effectively interact with Bitcoin data, hBK provides structured representations of common Bitcoin data elements:

• UTXO: Represents an unspent transaction output with details like transaction ID, value, and the public key script.
• Transaction: Contains information about a Bitcoin transaction, including inputs, outputs, and the block that contains the transaction.
• Input/Output: Represent individual inputs and outputs of a transaction, with details such as the value and script signatures.
• BitcoinHeader: Contains metadata about a Bitcoin block, such as its height, hash, and Merkle root.

These structures are essential for working with Bitcoin data, enabling developers to handle transactions and UTXOs efficiently within their dApps.

How to Use hBK Functions

The hBK makes it easy to query Bitcoin data using smart contracts. Here’s how some of the key functions work:

• Get Bitcoin Address Balance:
  function getBitcoinAddressBalance(string calldata btcAddress) public view returns (uint256 balance)
  Use this to fetch the balance of any Bitcoin address in satoshis. This call accesses the Bitcoin state stored in the hVM and returns the balance directly.
• Retrieve UTXOs:
  function getUTXOsForBitcoinAddress(string calldata btcAddress, uint256 pageNumber, uint256 pageSize) public view returns (UTXO[] memory)
  This function retrieves UTXOs for a Bitcoin address, allowing developers to work with unspent outputs in their applications.
• Get Transaction by ID:
  function getTransactionByTxId(bytes32 txId) external view returns (Transaction memory)
  Fetches detailed information about a specific Bitcoin transaction, including inputs and outputs.
• Get Block Header:
  function getLastHeader() public view returns (BitcoinHeader memory)
  Retrieves the latest Bitcoin block header, providing the most recent snapshot of the Bitcoin blockchain.

These functions are vital for building dApps that interact with Bitcoin’s state, whether for tracking balances, building wallets, or managing UTXO-based systems.

Benefits of Using hBK

The Hemi Bitcoin Kit offers several advantages over existing Bitcoin-Ethereum interoperability solutions:

1. Ease of Development: With hBK, accessing Bitcoin data is as simple as making a smart contract call. There’s no need to design complex contracts that handle relayed data.
2. Rich Data Access: hBK provides access to Bitcoin’s UTXOs, balances, and transaction details, data that would be impractical or impossible to retrieve using other methods.
3. Security and Reliability: Since hBK operates natively within the Hemi blockchain, dApps can access real-time Bitcoin data without relying on third-party relayers or trusted oracles.
4. Composability: Developers can design new layers of Bitcoin-Ethereum DeFi infrastructure, enabling others to build on top of their work seamlessly.
5. Cost-Effectiveness: hBK’s approach eliminates the need for costly gas-intensive proofs or third-party services, making it more efficient to develop and run Bitcoin-aware dApps.

Use Cases for the Hemi Bitcoin Kit

The possibilities for using hBK are vast. Some of the most promising use cases include:

• Custom Bitcoin Tunnels: Developers can create bespoke solutions for moving assets and data between Bitcoin and Ethereum in a trustless manner.
• Trustless BTC Staking: By integrating Bitcoin into DeFi applications, developers can unlock new opportunities for BTC holders to earn yield.
• Cross-Chain DAOs: Hemi DAOs can operate across both Bitcoin and Ethereum, allowing stakeholders from both communities to participate in governance.
• Bitcoin MEV Marketplaces: Create new markets for Bitcoin transaction ordering, leveraging hVM’s direct access to Bitcoin’s transaction data.

Getting Started with hBK

To begin building with hBK, developers can use the smart contract interfaces provided, or they can interact with the hVM precompiles directly for more advanced control. The Hemi Bitcoin Kit abstracts much of the complexity, making it easier for developers to focus on the features of their dApps rather than dealing with the intricacies of Bitcoin’s blockchain.

As future protocol upgrades are rolled out, including support for Bitcoin metaprotocols like Ordinals, BRC-20s, and Runes, the range of dApps that can be built on Hemi will expand further. This positions hBK as the go-to toolkit for developing sophisticated cross-chain applications.

By simplifying access to Bitcoin data, hBK enables developers to create innovative applications that leverage the strengths of both blockchains. Whether you’re building custom Bitcoin tunnels, DeFi platforms, or multichain DAOs, hBK offers the tools to bring your ideas to life.