Senior Blockchain Engineer · Poland · Global B2B

Custody infrastructure for systems that hold real money.

I design and build the backend paths that hold and move digital assets: key management, signing, transaction lifecycle, reconciliation and multi-chain integrations for startups and regulated financial institutions.

Seven-plus years across blockchain, fintech and enterprise backends. Bitcoin, EVM, Solana and permissioned networks.

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Selected work

Bank tokenization platform: Architected seven-plus Java and Spring Boot services covering token operations, payments, scheduling and reconciliation with a bank core system. Delivered live migrations on a running platform with zero post-merge production regressions.
Solana token infrastructure: Built Token-2022 flows, Meteora liquidity, Jupiter swaps, Squads Multisig V4 governance and GCP KMS-backed signing as one end-to-end operating path.
Enterprise DLT networks: Delivered permissioned financial networks with Hyperledger Besu, GoQuorum, Canton/Daml, FireFly and Kaleido across Terraform-managed environments.
WORK token launch: Led development of the WORK token at Paidwork, reducing transaction costs by 99% for a 17-million-user platform through L2 rollups. The contract was publicly audited. CoinMarketCap · audit

What I work on

Custody and wallets: KMS/HSM signing, multisig and MPC coordination, policy engines, deposit detection, transaction state machines, reorg handling and ledger reconciliation.
Multi-chain systems: Bitcoin and UTXO semantics, EVM and account abstraction, Solana programs and token accounts — without forcing one chain's model onto another.
Fintech backend: Java/Spring Boot and TypeScript/NestJS microservices, event-driven systems, PostgreSQL ledgers and high-integrity transactional workflows.
AI-assisted delivery: Agent workflows, MCP servers and review automation with deterministic guardrails, explicit evidence and human accountability for the final result.

Writing

Field notes from systems where a missed edge case can move money, corrupt a ledger or produce evidence nobody can reproduce.

Balance at 14:00 UTC Does Not ExistAug 2026
Money in Rust: Making Illegal States UnrepresentableJul 2026
Your Backtest Is Lying to YouJul 2026
Why Your Deposit Detection Misses MoneyJul 2026
Transaction State Machines for Multi-Chain CustodyJul 2026
UTXO Coin Selection in ProductionJul 2026

Working stack

BlockchainSolana, Rust, Anchor, Solidity, Besu, GoQuorum, Canton/Daml

BackendJava, Spring Boot, TypeScript, NestJS, Node, Python

DataPostgreSQL, RabbitMQ, Redis, Liquibase, IPFS

DeliveryAWS, GCP, Kubernetes, Terraform, Docker, ArgoCD, Helm

Background

Software house co-founder: Co-founded and ran a 15-developer software house across architecture, delivery, budgeting and client relationships.
Education: B.Eng. in Computer Science, Artificial Intelligence specialization, GPA 5.0. Certified Ethereum Expert and Certified Ethereum Developer.

Need a custody system reviewed or untangled?

See fixed-scope engagements, write to contact@maciejlewandowski.dev or reach me on LinkedIn.