We need a backend for BTC. For this work, it is assumed that the DEX operator has access to a full node with txindex, and that queries will be performed using the blockchain node software's standard RPC.

Part of this work will involve creating some common DEX interfaces. I anticipate there will be an interface for the asset backend itself, one for UTXOs, and probably some for transactions and blocks. These interfaces will necessarily need to be defined in a separate module. This work should also be coordinated with the analogous DCR backend development (#3), so that the interface can be accommodating for both. The DCR and BTC backends will be baked-in, but the interfaces defined during this work will also be used for plugins.

The asset backend will need to have at least the following functionality.

• Retrieve UTXOs
• Broadcast notifications for new blocks and mempool transactions
• Validate signatures
• Calculate script sizes (some script sizes might be constants)