Privacy-Preserving Citizenship Verification Using Zero-Knowledge Proofs and Taiwan's National ID Card

How can a user prove they are a Taiwanese citizen to an online service — without revealing their name, national ID number, or any other personal information? This talk presents our answer: a zero-knowledge proof system built on top of Taiwan's Citizen Digital Certificate (自然人憑證), a government-issued smart card that can produce RSA signatures.

Using the OpenAC proving framework, we designed a ZKP circuit that parses and verifies the RSA signature produced by the card, while keeping all personally identifiable fields hidden inside the proof. The entire flow runs on-device: the app requests a signature from the card for a given challenge, generates the zero-knowledge proof locally, and submits only the proof to a verifier. The verifier learns that the prover holds a valid Citizen Digital Certificate — and nothing else.

To make this accessible to developers, we have released an open-source SDK and a reference application covering the full pipeline: card interaction, signature acquisition, on-device proof generation, and backend verification.

In this session we will cover:

How ZKP and the Citizen Digital Certificate work together RSA signature circuit design and the OpenAC framework Performance challenges and optimizations for on-device proof generation SDK architecture and a live demo If you are interested in privacy-enhancing technologies (PET), decentralized identity (DID), or cryptography applied to civic tech, this talk offers a complete view from theory to working implementation.