Company: X Location: Remote-friendly globally. Time-zone band UTC-1 to UTC+5 (meaningful Saudi hours overlap). Optional relocation to Riyadh. Reports to: Custody Platform Lead. Type: Full-time. Individual Contributor. About us: The company is the digital-asset custody and infrastructure platform for the GCC. We hold institutional crypto safely, settle transactions across chains, and expose all of that as a developer API and a regulated-grade institutional console. The role You are a senior backend engineer with a custody and key-management background. You will be a foundational engineer on the company's custody platform, reporting to the Custody Platform Lead. You will: Ship production custody code across signing service, key management, chain integrations, and the transaction pipeline. Own a chain or a subsystem. Within 3 months you should own a meaningful surface end-to-end (a chain integration, a signing-service component, a key-rotation flow). Pair with the Custody Platform Lead and our in-house cryptography function on threshold signing, share generation, and key recovery flows. Write post-mortems when things break. We treat these as architecture-improvement opportunities, not blame exercises. Integrate new chains. Bitcoin, Ethereum and L2s, Solana, and an active onboarding queue. Engage in async written communication. Spec docs, PR descriptions, async design reviews. Must-haves 5-plus years of backend engineering, with the last 2-plus years on a custody platform or a key management system at a regulated entity. General fintech does not substitute. Hands-on with at least one of: HSM lifecycle (CloudHSM, YubiHSM, Ledger Vault, similar). MPC / TSS (Fireblocks-style, Sepior, ZenGo, Curv-style). Threshold signing schemes (GG18, GG20, FROST, CGGMP21, CMP). Production experience with one or more of: Bitcoin (UTXO model, PSBT). Ethereum (EIP-712, EIP-1559, account abstraction). At least one non-EVM Layer 1 (Solana, Sui, Cosmos SDK chain, similar). Reads Solidity, Move, or Rust well enough to integrate with new chains without hand-holding. Strong async written communication. Your PR threads, design docs, and intro reply are themselves a signal. English fluency. Nice-to-haves Experience with travel-rule / FATF compliance integrations (Notabene, Sumsub, TRP, IVMS101). Authored or contributed to an EIP, BIP, or chain RFC. Audit-contest finalist on Code4rena, Sherlock, or Cantina. Familiarity with regulated-financial controls: dual-control, four-eyes, M-of-N approvals, SOC 2 evidence collection. This is not the right role if Only frontend / dApp experience, no backend custody or key-management depth. "Crypto trader who codes." Algorithmic trading without custody experience. Anyone whose entire blockchain experience is a single hackathon, bootcamp, or DeFi side project. Currently subject to a non-compete blocking digital-asset custody for more than 6 months. Stack Backend: Go primary. Some Rust, some TypeScript. Aurora Postgres and ClickHouse. Temporal for orchestration. Cryptography: in-house MPC stack (TSS-based), HSM integrations, multi-chain signing service. Chains: Bitcoin, Ethereum and L2s, Solana, active onboarding queue. Infra: AWS, Kubernetes, GitHub Actions CI, Terraform. Security posture: SOC 2 Type II in motion, SAMA-aligned, intent toward ISO 27001 and dual-control workflows. Location, visa, relocation Location: Riyadh, open to Remote Opportunity. Time-zone band: UTC-1 to UTC+5 for meaningful Saudi-hours overlap. Relocation (optional): if the candidate elects to relocate to Riyadh, we’ll support sponsorship. Tax / payroll: KSA payroll for relocators. Contractor or Employer-of-Record for remote-international.