Revolutionizing Security with Biometric-Bound Credentials: A New Era in Digital Identity

As we step further into the digital age, safeguarding personal and sensitive data has become paramount. Passwords, once the cornerstone of online security, are increasingly proving inadequate in the face of advanced cyber threats and usability challenges. In this landscape, hardware-based authentication methods like passkeys offer a promising alternative. However, they are not without their limitations. The pressing need for more versatile and secure solutions has led to the emergence of biometric-bound credentials—an innovative approach that promises to reshape digital identity management.

The Case for Biometric-Bound Credentials

Passkeys, primarily supported by FIDO (Fast Identity Online) protocols, function as secure hardware tokens designed to eliminate the vulnerabilities of traditional passwords. However, these tokens pose significant challenges in account recovery. When users are tied to their devices—literally and figuratively—loss, damage, or theft of a device can lead to irrevocable access issues. Imagine dropping your phone into water or losing it during travel; with hardware-bound authentication, your digital identity may sink with it.

To address these challenges, biometric-bound credentials have been proposed as a transformative solution. By leveraging the unique attributes of biometrics, these credentials offer enhanced security while preserving user convenience.

Understanding Biometric-Bound Credentials

A Biometric-bound credential refers to a digital credential that is linked directly to a person's unique biological characteristics, like their fingerprint or facial features, essentially using their biometrics as the primary means of verification for accessing systems or services, offering a more secure and convenient way to authenticate identity compared to traditional passwords or PINs. 

There are several ways to create biometric-bound credentials. Biometric cryptosystems such as Trust Stamp’s Stable IT2 work by creating a stable key from biometrics, whereas encrypted biometrics simply encrypt biometric templates, which must be decrypted during comparison, therefore offering no protection during the comparison phase. Homophic encryption biometrics address this weakness, albeit at the cost of higher computation.

Finally, SMPC proposes to distribute biometric templates into multiple compute nodes, but it incurs the highest computation, not to mention that the biometric comparison must be done online, so it is not suitable for time-critical applications such as border controls.

As shown in the table below, the biometric cryptosystem stands out in terms of template protection, online/offline, and low computational requirements.

In addition, specific to Trust Stamp’s Stable IT2 is its ability to extract a high entropy of 256 bits that is completely independent of the biometric sample. This approach directly binds biometrics to cryptographic keys.

During registration, a stable key is created from the enrolment biometric sample but immediately discarded. The registration process generates a sketch that does not reveal the biometric or the secret (the stable key). When a user attempts authentication, the system reconstructs the stable key from a new biometric sample. Since only the registered user can provide a close enough biometric sample for the reference, this method ensures a strong, irreversible binding between the credential and the user’s biometric data. 

Trust Stamp’s implementation further incorporates advanced techniques such as:

• Cancellable biometrics: Transforming biometric templates into a secure, cancellable format.
• Secret splitting (sharding): Distributing biometric data across multiple nodes for secure storage.
• Encryption: Safeguarding any data through cryptographic encryption.
• Liveness detection: Ensuring that the biometric input is from a live individual rather than a spoof or artifact.
  
  

Key Advantages and Applications

Biometric-bound credentials are gaining traction across various domains, offering unique advantages over traditional methods:

1. Enhanced Security
   Unlike hardware tokens, where private keys are stored on the device, biometric cryptosystems like Trust Stamp’s Stable IT2 reconstruct keys from biometric data. This eliminates the risk of key theft and provides a robust defense against unauthorized access.
2. Account Recovery
   Stable IT2 enables seamless account recovery without compromising security. Users can regain access to their accounts by providing their biometrics, even if they lose their primary authentication device.
3. Multi-Factor Authentication (MFA)
   By design, biometric-bound credentials comply with high-security standards such as NIST AAL2 and AAL3, ensuring robust multi-factor authentication.
4. Versatile Applications
   The potential use cases for biometric-bound credentials are vast, including:
   • Digital wallets: Securely managing financial transactions.
   • Remote identity proofing: Verifying identity for online services.
   • Digital travel credentials: Streamlining border control processes.
   • Biometric-enabled passes: Facilitating secure access through QR codes.

Overcoming Challenges

While biometric-bound credentials offer significant promise, they also face challenges. Traditionally, a biometric cryptosystem can only extract some 30+ and certainly no more than 60 bits of entropy per biometric sample of the same modality. Innovative solutions like Stable IT2 address this by generating high-entropy keys from biometrics, ensuring randomness and security.

Additionally, public understanding of key concepts remains limited. For instance:

• Credentials should not be confused with tokens.
• Identity proofing differs from authentication.
• Biometric identification is not the same as identity proofing.
• The robustness of offline biometric comparison against the disruption of internet connectivity is often underappreciated.

Clear communication and education are essential to bridge these gaps and drive adoption.

Looking Ahead

As organizations and governments increasingly adopt biometric-bound credentials, partnerships will play a critical role in scaling their impact. Trust Stamp, for instance, seeks collaborations with biometric vendors across various modalities to expand the reach of Stable IT2.

The transition from traditional security methods to biometric-bound credentials represents a paradigm shift in how we manage digital identities. By addressing the limitations of hardware tokens and enhancing security through biometrics, this innovative approach is set to redefine authentication in a digital-first world.

For researchers, practitioners, and regulators alike, the journey toward widespread adoption of biometric-bound credentials is both exciting and essential. With the right combination of technology, policy, and education, we can build a future where digital security is not just robust but also intuitive and user-friendly.

A similar version of this article has been accepted for publication by the Biometrics Institute's editorial team in their upcoming publication series: "Future of Responsible Biometrics"