> For the complete documentation index, see [llms.txt](https://docs.bitcoinos.build/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.bitcoinos.build/technical-documentation/grail-pro-charms-zkbtc/technical-overview/grail-pro/grail-pro-system-architecture/backend.md).

# Backend

Design: A horizontally scalable, trustless service employing a decentralized queue-based architecture for processing tasks in an orderly manner.

Tasks: Scans integrated blockchains for relevant transactions, stores them in a dedicated database (without secrets or personally identifiable information), generates ZK-proofs (using schemes like Groth16), and handles transaction formation, validation, tracking, and error management via HTTP API endpoints.

Workflow: Detects payments, creates bridging transactions (e.g., locking BTC to mint zkBTC or burning zkBTC to release BTC), and forwards unsigned transactions to operators via a simple message broker. Collects signatures and publishes once the threshold is met. Supports complex transactions with multiple inputs/outputs for batching user payments.

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