Senior / Staff Software Engineer, Mobile — Core (Account & Risk)

United States Digital Space LLC; Hong Kong; On-site; HKD 900,000 - 1,300,000; Full time

Job summary

United States Digital Space LLC is seeking a Staff Mobile Platform engineer to own account security and authentication subsystems for iOS and Android. You will shape secure flows, collaborate with risk and security teams, and drive automation in engineering workflows.

Strong background in native mobile development, Rust with UniFFI, and experience with Passkey/WebAuthn is highly valued. Apply your AI expertise to improve delivery quality and reliability.

Qualifications

• Experience building native iOS and/or Android apps.
• Cross‑platform or shared‑logic architecture experience.
• Strong knowledge of Rust and UniFFI.
• Hands‑on security in mobile auth: OAuth/OIDC, MFA, Passkey / WebAuthn.
• Proficiency with Swift, Kotlin, or other major mobile languages.

Responsibilities

• Own account subsystem design and security across iOS/Android platforms.
• Design secure, low‑friction login and authentication flows at scale.
• Collaborate with risk & security for threat models and defenses.
• Build AI‑native engineering practices for automated development workflows.
• Lead code reviews and raise engineering quality across teams.
• Set technical direction beyond your subsystem and influence cross‑team decisions.

Skills

iOS/Android native

Cross‑platform knowledge

Rust

UniFFI

Swift

Kotlin

React Native

Flutter

Security fundamentals

OAuth/OIDC

MFA

WebAuthn

Keychain/Keystore

Passkey

Java

JavaScript

Tools

UniFFI

Keychain/Keystore

WebAuthn

Job description

the company will be prioritising applicants who have a current right to work in Hong Kong, and do not require the company's sponsorship of a visa.

Who We Are

At the company, we believe that the future will be reshaped by crypto, and ultimately contribute to every individual's freedom.

the company is a leading crypto exchange, and the developer of the company Wallet, giving millions access to crypto trading and decentralized crypto applications (dApps). the company is also a trusted brand by hundreds of large institutions seeking access to crypto markets. We are safe and reliable, backed by our Proof of Reserves.

Across our multiple offices globally, we are united by our core principles: We Before Me, Do the Right Thing, and Get Things Done. These shared values drive our culture, shape our processes, and foster a friendly, rewarding, and diverse environment for every OK-er.

the company is part of OKG, a group that brings the value of Blockchain to users around the world, through our leading products the company, the company Wallet, OKLink and more.

About The Team

Own the account backbone of a CeFi platform trusted by millions — login, registration, account security, MFA, Passkey — where a single security regression is measured in real user funds. The more senior you are, the more you set the technical direction others build on.

What You'll Be Doing

• Own account-system subsystems end-to-end — authentication, MFA, Passkey/WebAuthn, session & device trust, account registration and recovery — including architecture, tradeoffs, and long-term evolution.
• Design flows that are secure and low-friction at millions-of-DAU scale — the hardest tradeoff in this space.
• Partner with risk & security teams to turn threat models into shipped mobile defenses.
• Build our AI-native engineering practice — design automated development workflows and harness systems (agents, evals, guardrails, CI integration) that let AI do real engineering work, while safeguarding delivery quality and efficiency.
• Raise the bar through design and code review, and by making the engineers around you better.
• At the Staff level: set technical direction beyond your own subsystem and drive cross-team, cross-timezone decisions that shape the account platform.

What We Look For In You

• Deep, hands‑on experience building native iOS and/or Android — you understand the platform, not just a framework on top of it.
• Experience with a cross‑platform / shared business‑logic layer. We build ours in Rust + UniFFI; direct Rust-on-mobile experience is a strong plus, but experience with any shared‑logic approach — KMP, Flutter, or React Native — transfers well and is valued.
• Fluent in at least one of: Swift / Kotlin / Rust / Objective‑C / Java / JavaScript, with strong CS fundamentals.
• Architecture experience with large‑scale mobile apps — you’ve applied maintainable design patterns and own solutions from requirements through to production.
• Hands‑on with mobile authentication & security — OAuth/OIDC, MFA, secure storage (Keychain/Keystore), biometrics. Direct experience with Passkey / WebAuthn / FIDO2 is a strong advantage — it’s live in our stack and central to what you’ll work on.
• Solid grasp of threat modeling and the mobile attack surface.
• You apply AI deeply in your own engineering — not just code generation. You’ve built, or are driven to build, automated development workflows and harnesses that make delivery both faster and more reliable. Solid grasp of LLM fundamentals, prompt engineering, RAG, and agent concepts, with hands‑on experience taking an AI pipeline from scratch to shipped.