Background. One-time mobile authentication remains vulnerable to post-login compromise. Biometric templates, once exposed, cannot be revoked. Continuous authentication that models user behavior and physiology over time can raise security, but it must preserve privacy and resist spoofing and replay.
Methods. We propose a layered framework centered on a user's Digital Twin built from continuous, multimodal signals gathered passively from a smartphone and a companion wearable. The pipeline includes sensor ingestion, feature extraction, adaptive DT modeling per modality, context-aware fusion into a unified confidence score, and a decision module for seamless access, step-up challenges, or lockout. Privacy is enforced through template encryption, hardware-backed secure storage, and the use of zero-knowledge proofs and homomorphic encryption for verifications involving remote services.
Results. We conduct a theoretical security evaluation using the STRIDE methodology. The analysis maps threats such as spoofing, tampering, information disclosure, denial of service, and elevation of privilege to architectural mitigations, including multimodal liveness, secure enclaves for DT parameters, encrypted storage and transit, adaptive sensing, and fail-safe locks on precipitous confidence drops. A worked example illustrates how confidence responds to legitimate and illegitimate use and how the DT adapts during high-confidence sessions.
Discussion. The framework aims to balance the usability-security-privacy trilemma by achieving passive, high-fidelity verification while constraining data exposure through cryptographic protocols. We discuss deployment considerations such as energy management, computational overhead of cryptography, inclusivity and bias, and regulatory and ethical expectations in healthcare contexts, including consent and transparency. Limitations include the absence of empirical validation, reliance on secure hardware and wearables, and the need for dedicated adversarial ML defenses.
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