Project notebook / Systems
DocumentedHardening iOS Device Trust Signals
I hardened iOS device-trust decisions by separating untrusted client signals from evidence verified by backend services.
What I built
- I defined server-issued nonce challenges, separated verifiable evidence from advisory device signals, and implemented rejection paths for stale, replayed and mismatched requests.
Experiments & checks
- Check nonce freshness, binding, and replay rejection at the API boundary.
- Treat instrumentation and device posture claims as advisory unless independently verified.
- Exercise outage and fallback paths for privileged actions.
Notes & limitations
Client-side device posture was being treated as stronger evidence than the backend could verify. That created room for replay and manipulated signals in high-risk decisions.
Needed to preserve user experience under partial outages while still failing closed for privileged actions.
I made the verification boundary explicit: backend evidence could inform a privileged decision, while client posture alone could not. The case study focuses on that design and its failure paths, rather than publishing private system telemetry.
Screenshots & media
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