Workload: full-time, remote Start: asap Duration: long-term Location: any English: B2
Technical requirements (general) - 3+ years of production blockchain experience in BTC. Multi-protocol experience (strongly preferred). - Java + Spring Boot + SQL - Familiarity with test-driven development (TDD) and/or behaviour-driven development (BDD) as working practices, writing tests before or alongside implementation. - Familiarity with Domain-Driven Design principles. - Comfortable working in a monorepo structure with shared libraries, cross-squad code visibility, and coordinated CI/CD pipelines. - Proactive communication, raising blockers, design concerns, and cross-squad dependencies. - Written and verbal communication in English must be at a professional level.
Technical requirements (specific) - Deep Bitcoin protocol expertise: PSBT format (BIP-174 and subsequent updates), UTXO management and coin selection algorithms, SegWit transaction structures, script types and descriptor formats (Taproot out of scope). - Multi-signature coordination: BIP-48 (multi-sig derivation paths), BIP-67 (lexicographic key sorting), P2WSH script construction, PSBT combination and finalisation workflows. - Fee estimation: Mempool analysis, RBF (Replace-By-Fee) and CPFP (Child-Pays-For-Parent) fee bumping strategies, fee rate prediction. - Transaction construction: Witness data assembly, BIP-143 (SegWit sighash), DER signature encoding, low-S enforcement. Familiarity with sighash types. SIGHASH_ALL is the production default for custody; engineers should understand the full sighash taxonomy for validation and edge-case handling but implementation focuses on SIGHASH_ALL. - Transaction lifecycle and remediation: Stuck transaction detection via mempool monitoring, RBF and CPFP execution for fee bumping, handling transactions that remain unconfirmed for extended periods, and managing the operational decision of when to replace vs wait. - UTXO indexing and balance management: Experience with UTXO set tracking, balance computation from unspent outputs, UTXO consolidation strategies during low-fee windows, and address-level balance monitoring for deposit detection. - Address management: Gap limit handling for HD wallets, change address allocation from internal derivation branch (m/84'/0'/0'/1/*), address reuse prevention, and descriptor-based address discovery for wallet import and recovery scenarios. - Chain semantics and failure modes: Understanding of Bitcoin's probabilistic finality (confirmation depth vs settlement assurance), dust output limits and their implications for UTXO management, fee spike behaviour during congestion events (e.g. ordinals, inscription surges filling blocks for extended periods), double-spend detection for unconfirmed transactions, and the operational difference between a transaction that is "broadcast" vs "in mempool" vs "confirmed at depth N." Engineers must understand that Bitcoin has no concept of a "failed" transaction that consumes fees; a transaction either confirms or it doesn't, and unconfirmed transactions can be replaced or may eventually confirm unexpectedly. - Production experience: Operating Bitcoin custody or wallet infrastructure at institutional scale, not testnet-only or personal wallet experience.
Candidate's responsibilities Bitcoin wallet management, UTXO handling, transaction construction (PSBT, SegWit), multi-signature coordination, fee estimation.
