In today’s digital world, verifying someone’s identity online is a challenging task, especially when balancing the need for privacy with security requirements. Many applications, from social platforms to financial systems, need to verify key details like nationality, age, or identity uniqueness, but current solutions are often intrusive, centralized, and susceptible to data breaches.
Enter zero-knowledge proofs (ZKPs) combined with electronic passports. With ZKPs, it’s possible to prove something is true—such as a person’s nationality or age—without revealing the actual data. Electronic passports, used by more than 170 countries worldwide, already provide a verified digital footprint of individuals. These passports contain chips with personal information that can be verified without disclosing it entirely. Using zero-knowledge proofs to verify identities via passports offers a compelling solution that could drastically enhance privacy in various online and offline applications.
Let’s explore how this approach works, the underlying mechanisms, and the potential applications and limitations of such a system.
The Concept of Zero-Knowledge Proofs
Zero-knowledge proofs (ZKPs) are a cryptographic method that allows one party (the prover) to prove to another party (the verifier) that a statement is true without revealing any additional information about the statement. In the case of identity verification, ZKPs can confirm someone’s identity or attributes (such as age or nationality) without exposing sensitive personal data.
This concept can be paired with electronic passports, which are issued with a digital signature from the country’s authorities, allowing users to securely store their identity information in a verifiable format. These passports contain an NFC chip that stores essential personal details, including name, date of birth, nationality, and even a photo. The public keys used to verify these passports are available in global registries maintained by governments.
Verifying Identity with Zero-Knowledge Proofs and Passports
A significant challenge in online identity verification is that most systems require users to disclose too much personal information. However, using ZKPs in conjunction with electronic passports can change this dynamic by enabling selective disclosure—users can verify their identity while revealing only the necessary details.
Here’s how the process works:
- Reading the Passport Chip: With any NFC-enabled smartphone, a user can scan the NFC chip in their electronic passport to extract their personal information.
- Creating a Zero-Knowledge Proof: Instead of sharing all personal data, the user can generate a ZKP that proves the accuracy of selected attributes, such as nationality or age, without sharing any other details.
- Signature Verification: The ZKP verifies that the disclosed attributes (such as name, nationality, or date of birth) have been signed by a legitimate country authority. This is done by checking the public key of the issuing country, ensuring that the passport is valid and the data is authentic.
This approach means users no longer have to disclose all their personal data just to prove one or two details. For example, a user could prove they are over 21 years old to access age-restricted services without revealing their actual date of birth.
Enhancing the System: Features and Use Cases
For the system to be both secure and practical, certain additional features are necessary.
1. Public Key Verification with Merkle Proofs
One challenge in using public keys for verification is ensuring that the key comes from a legitimate country listed in the International Civil Aviation Organization (ICAO) registry. This problem is addressed using Merkle proofs. Instead of directly passing the public key, a Merkle proof can verify that the public key is part of the global registry. This ensures that only passports issued by recognized authorities can be verified.
2. Selective Disclosure with Bitmaps
One key feature is the ability to selectively disclose only specific attributes. By using a bitmap as an input to the ZKP, the user can choose which attributes to disclose. For example, they might choose to reveal only their nationality and age while keeping other information, such as their name or passport number, private.
3. Range Checks for Age Verification
For certain applications, such as age-restricted services, users need to prove they are above a certain age without revealing their exact date of birth. A range check in the ZKP circuit can prove that the user is above a specified age while keeping their precise age confidential. This feature can be particularly useful for verifying legal drinking ages, voting eligibility, or access to adult content.
4. Sybil Resistance and Passport Expiry Checks
In applications like decentralized voting or fair airdrops, sybil resistance (preventing one person from creating multiple identities to game the system) is crucial. A hash of the government’s signature on the passport can be stored to ensure that the same passport cannot be used multiple times.
Moreover, verifying that a passport is still valid (i.e., not expired) can be done by comparing the expiry date with the current date using a blockchain timestamp or server-side verification.
Real-World Applications of Zero-Knowledge Proofs with Passports
The combination of zero-knowledge proofs and electronic passports opens up numerous possibilities for secure, privacy-preserving identity verification in various industries.
1. Proof of Humanity and Sybil Resistance
One of the most important applications is proof of humanity for sybil resistance. Ensuring that each individual can only use one verified identity can prevent bots and fake accounts from taking over platforms. This is especially relevant in voting systems, airdrops for token distribution, or decentralized social media platforms that need to verify unique users without compromising privacy.
2. Privacy-Preserving Age Verification
Governments and businesses often need to ensure that minors cannot access certain services, such as purchasing alcohol or gambling. Zero-knowledge proofs can verify age without revealing exact birth dates. This allows for privacy-preserving age checks at bars, casinos, or online services while complying with legal regulations.
3. Compliance for Decentralized Finance (DeFi)
Another compelling use case is in DeFi. Many financial platforms require users to prove they are not citizens of certain countries to comply with local laws. With selective disclosure, users can prove that they are not from restricted countries without revealing their full nationality or personal details, striking a balance between compliance and privacy.
4. Authentication for Transaction Signing
Electronic passports could also be used as authentication tools for signing blockchain transactions. Some passports support active authentication, meaning they have their own private keys and can sign data. This could be used for small transactions or multisignature setups, where the passport acts as one of the authorized signers.
Limitations of Using Passports for Zero-Knowledge Proofs
While the potential for using electronic passports and ZKPs is vast, certain limitations need to be considered.
- Biometric Checks Are Missing: Electronic passports do not perform biometric checks when the chip is read. This means someone could theoretically use a stolen or borrowed passport for identity verification, although additional layers of security could mitigate this risk.
- Passport Ownership Rates: Not everyone in the world possesses a passport. For instance, only about 50% of the U.S. population has a passport, limiting the scalability of this approach.
- Passport Revocation and Dual Citizenship: Passports can be lost, revoked, or replaced without invalidating prior signatures. Additionally, dual citizenship complicates identity verification when multiple passports are involved.
These limitations highlight the need for multi-layered identity verification systems that combine various sources of identity proof.