Middle Bitcoin / Blockchain Engineer (Java)

PioGroup Software is a team of professionals passionate about building reliable digital products. We are looking for an experienced Strong Middle Blockchain Engineer with strong production experience working with the Bitcoin protocol and Bitcoin wallet/custody infrastructure.
The main focus of the role is developing and maintaining Bitcoin wallet infrastructure, including UTXO management, transaction construction and signing, PSBT, SegWit, multi-signature flows, fee management, and transaction lifecycle handling.
For this position, hands-on production experience specifically with the Bitcoin protocol is essential. General blockchain or Web3 experience alone is not sufficient.
Requirements
3+ years of production experience with Bitcoin / BTC infrastructure.
Hands-on experience with Bitcoin-based protocols, UTXO model, PSBT, and BIP standards.
Strong experience with Java, Spring Boot, and SQL.
Experience working with production wallet or custody infrastructure.
Good understanding of TDD and/or BDD practices.
Familiarity with Domain-Driven Design principles.
Experience working in a monorepo environment with shared libraries and coordinated CI/CD pipelines.
Professional written and spoken English.
Proactive communication and ability to raise blockers, technical concerns, and cross-team dependencies.
Bitcoin Protocol Expertise
We expect strong practical knowledge of:
PSBT and BIP-174.
UTXO management and coin selection.
SegWit transaction structures.
Bitcoin script types and descriptor formats.
HD wallets and derivation paths.
BIP-48 and BIP-67.
P2WSH and multi-signature transaction flows.
PSBT combination, signing, and finalisation.
Witness data and BIP-143.
DER signature encoding, low-S enforcement, and sighash types.
UTXO indexing and balance calculation.
Address discovery, gap limits, change address allocation, and address reuse prevention.
Transaction Lifecycle & Fee Management
Production experience with:
Mempool monitoring.
Fee estimation and fee-rate prediction.
RBF (Replace-By-Fee).
CPFP (Child-Pays-For-Parent).
Stuck transaction detection.
Transaction replacement and rebroadcasting.
Confirmation monitoring.
Double-spend detection.
UTXO consolidation during low-fee periods.
Candidates should also clearly understand the operational difference between a transaction being:
Broadcast.
Accepted into the mempool.
Confirmed.
Confirmed at depth N.
A strong understanding of Bitcoin probabilistic finality, dust limits, fee spikes during network congestion, and the behaviour of unconfirmed transactions is also required.
Responsibilities
Develop and maintain Bitcoin wallet infrastructure.
Manage UTXOs and wallet balances.
Construct Bitcoin transactions.
Work with PSBT and SegWit.
Implement multi-signature transaction flows.
Handle fee estimation and fee bumping using RBF and CPFP.
Monitor mempool activity and transaction lifecycle.
Implement deposit detection and address-level balance monitoring.
Support wallet recovery and descriptor-based address discovery.
Participate in technical design and architecture decisions.
Collaborate with other engineering squads and shared platform components.
Nice to Have
Experience with multiple blockchain protocols.
Experience with institutional-grade custody or wallet platforms.
Experience working with systems processing high volumes of Bitcoin transactions.
Important: we are specifically looking for candidates with documented commercial experience working with the Bitcoin protocol, including UTXO management, PSBT, SegWit, BIP standards, and the Bitcoin transaction lifecycle. Testnet-only, personal wallet, or exclusively Ethereum/Web3 experience will not be sufficient for this role.