Middle Blockchain & Fintech Engineer

**Blockchain & Finance Lead — UEX.US Platform** 📍 **Location:** Madrid, Spain (Hybrid — 3 days onsite) 🏢 **Company:** Quanta Tech Systems Europe (US-backed, Quanta Tech Systems LLC) 💼 **Employment:** Full-time, permanent (Spanish contract) 💰 **Salary:** €70,000 – €95,000 + bonus + token allocation About Us Quanta Tech Systems Europe is building the core infrastructure behind **UEX.US** — a next-generation, U.S.-regulated digital asset exchange (Wyoming, est. 2025). Our platform combines: - Crypto trading - Staking & yield products - Crypto-backed lending - Tokenized real-world assets (gold, silver, equities) We are scaling our Madrid HQ and looking for a **Senior Blockchain & Fintech Engineer** to take ownership of the most critical layer — where **code meets real money movement** . Your Mission You will be the **technical anchor** for blockchain and financial systems: - On-chain settlement - Wallet & custody infrastructure - Exchange core (matching, ledger, reconciliation) - Fiat ↔ crypto rails This is a **high-impact role** — your systems will directly move and secure real assets. What You’ll Do Blockchain Engineering - Build Go services interacting with: - EVM chains (Ethereum, Polygon, Arbitrum, Base) - Non-EVM (Bitcoin, Solana, XRP, Cardano) - Own wallet infrastructure: - HD wallets (BIP-32/39/44) - HSM / MPC integrations - Hot / warm / cold architecture - Develop: - Indexers & reorg-safe pipelines - Gas optimization tools - Integrate custody providers: - Fireblocks, Copper, BitGo - Review smart contracts & define listing security standards Finance & Exchange Systems - Work on: - Order book & matching engine - Ledger & settlement systems - Ensure: - Double-entry accounting - Idempotency - Cross-chain reconciliation - Build fiat integrations: - PayPal, Zelle, Apple Pay, cards - Implement: - Crypto-backed loans - Staking rewards - APY-based savings Leadership & Ownership - Act as **domain tech lead** (blockchain + finance) - Define: - Engineering standards - Observability & incident response - Mentor engineers & support hiring - Drive architecture via RFCs Must-Have - **Go (Golang)** — 4+ years in production systems - **Blockchain/Web3** — 2+ years (Ethereum or similar) - Strong understanding of: - Transactions, gas, nonce, reorgs - Cryptography (ECDSA, keccak) - **Fintech experience** : - Exchanges / payments / ledger systems - **Distributed systems** : - Kafka, PostgreSQL, Redis - **Cloud & Infra** : - AWS, Docker, Kubernetes, CI/CD - **Security mindset** : - Key management, attack vectors, front-running - 🤖 **Claude Code (required)** : - Daily usage - AI-assisted workflows - 🇬🇧 English — professional level Nice to Have - Solidity / Rust - Experience in: - Crypto exchange / neobank - Regulatory knowledge: - MiCA / FinCEN / SEC - MPC / HSM (CloudHSM, Vault, etc.) - Open-source contributions (geth, Bitcoin Core, etc.) - RWA (tokenized assets) experience Tech Stack **Languages:** Go, TypeScript, Solidity, Rust **Chains:** Ethereum, Polygon, Bitcoin, Solana, XRP, Cardano **Data:** PostgreSQL, Redis, Kafka, ClickHouse **Infra:** AWS, Kubernetes (EKS), Terraform **Security:** Vault, AWS KMS, Fireblocks, Chainalysis **Observability:** Prometheus, Grafana, OpenTelemetry **AI:** Claude Code, Claude Opus 4.7 💎 Compensation & Benefits - 💰 €70k – €95k salary - 📈 Bonus up to 15% - 🪙 Token allocation (vesting) - 💻 MacBook / Linux workstation + €2,000 setup - 📚 €2,500 learning budget (Devcon, EthCC, Money20/20) - 🏥 Private health insurance (Sanitas / Adeslas) - 🌴 25 vacation days + holidays - ✈️ Travel (NYC, London, Paris, Brussels) - 🌍 Relocation support + visa Hiring Process 1. Intro call (30 min) 2. Technical interview (Go + blockchain) 3. Take-home (paid): ERC-20 indexer 4. System design (custody + settlement) 5. VP Engineering interview 6. Offer (2–3 weeks total)