In today’s world, our digital identities are a huge part of our daily routines. We use them to access apps, services, and information with just a few taps. But this convenience can also put our privacy at risk. Many digital credentials can be used to track what we do online and even tie different activities back to us. This raises the question: how can we stay private while still using digital services?

The Problem with Linkable Digital Identities

When you use your mobile driver’s license or log into different apps, there are often hidden identifiers involved. These identifiers can connect your various online activities without your knowledge. This means your behavior, preferences, and location might be collected and analyzed, creating detailed profiles about you. Even if you only share limited information in each interaction, these identifiers can still link your activities together over time.

This linkability is a growing concern for privacy advocates and everyday users alike. It can lead to unwanted tracking, targeted advertising, or even surveillance. The challenge is to find ways to use digital credentials without allowing them to be connected across different uses. That’s where new privacy-enhancing tools come into play.

Introducing Crescent: A Privacy-Preserving Cryptographic Library

To combat the issue of linkability, a new tool called Crescent has been developed. Crescent is a cryptographic library designed to add unlinkability to common digital identity formats. It works by ensuring that each use of a credential remains separate unless the user explicitly chooses to share information. This means that even if someone uses their driver’s license multiple times, Crescent keeps those activities disconnected unless the user reveals specific data.

Existing privacy features like selective disclosure already let users choose what information to share. However, even with these, credentials can still be linked through serial numbers, cryptographic signatures, or embedded identifiers. Crescent goes a step further by preventing such linkages altogether, giving users more control over their digital footprints.

How Crescent Achieves Unlinkability

There are two main approaches researchers have explored for adding unlinkability to digital identities. One involves specialized cryptographic signatures that can prevent linking but require significant changes to current systems. Implementing these new algorithms and standards can be complex and time-consuming.

The other approach uses zero-knowledge proofs with existing credentials. Zero-knowledge proofs let users demonstrate they have certain information—like a valid driver’s license—without revealing the actual data. For example, a user could prove they live in a specific ZIP code without sharing their exact address or personal details. This method helps protect privacy while still verifying important information.

Crescent employs advanced techniques to make zero-knowledge proofs more practical. Since these proofs can be computationally heavy, Crescent uses preprocessing—performing complex calculations in advance—to speed things up. This makes it easier for users to prove what they need without exposing their full data or allowing their activities to be linked.

The Future of Private Digital Interactions

Crescent represents a major step forward in protecting digital identities from unwanted tracking. By enabling users to control how their credentials are used and shared, it helps keep online activities private and disconnected. This not only enhances individual privacy but also promotes a more trustworthy digital environment.

As technology evolves, tools like Crescent could become standard in digital identity systems. They offer a way to enjoy the convenience of online services without sacrificing privacy. Ultimately, the goal is to empower users with more control over their digital footprints and reduce the risk of surveillance and profiling.

Protecting digital privacy is increasingly important in our connected world. Innovations like Crescent show how cryptography and smart design can help us take back control and stay safe online.

Inspired by

• https://www.microsoft.com/en-us/research/blog/crescent-library-brings-privacy-to-digital-identity-systems/

Sources

• iacr.org
• identity.foundation
• github.com
• github.com
• aka.ms