Crescent digital identity privacy
In the interconnected world of digital identities, where electronic credentials like mobile driver’s licenses and workplace logins are commonplace, privacy concerns are becoming increasingly prominent. These credentials offer undeniable convenience but also expose users to the risk of tracking and surveillance through linkability.
This occurs when hidden identifiers within these credentials allow separate activities to be linked, creating detailed profiles of user behavior, especially regarding digital identity in the context of unlinkability, including privacy protection applications. Addressing this issue is crucial to maintaining individual privacy in digital interactions. Crescent, a cryptographic library, has been introduced to mitigate these privacy risks by adding unlinkability to widely used identity formats such as JSON Web Tokens and mobile driver’s licenses.
Crescent enhances existing privacy features by preventing credentials from being linked through serial numbers, cryptographic signatures, or embedded identifiers, particularly in digital identity, including privacy protection applications. By ensuring that only the information a user chooses to disclose is revealed, Crescent protects users’ privacy without requiring organizations to overhaul their current systems.
Cryptographic Privacy Digital Identity
Understanding how Crescent achieves unlinkability involves examining two primary methods researchers have developed for enhancing privacy in identity systems: ① Specialized Cryptographic Signature Schemes: These schemes, such as the BBS signature being standardized by the Internet Engineering Task Force (IETF), can provide unlinkability but necessitate significant changes to existing infrastructures. This involves standardizing, implementing, and integrating new algorithms into current software and hardware platforms, which can be a slow process.
② Zero-Knowledge Proofs with Existing Credentials: Used by Crescent, this approach allows users to prove specific facts about their credentials without exposing underlying data, preventing tracking. For instance, a person could verify they possess a valid driver’s license and reside in a certain ZIP code without disclosing additional personal information, particularly in digital identity in the context of privacy protection in the context of digital identity, especially regarding privacy protection.
By performing the most complex calculations in advance, Crescent ensures efficient proof generation, making it feasible for mobile devices. Beyond unlinkability, Crescent supports selective disclosure, enabling users to prove certain facts without revealing unnecessary details. This includes confirming the validity of a credential without disclosing unique identifiers like expiration dates, including digital identity applications, including privacy protection applications.
These protections remain robust even when credentials are stored in a phone’s secure hardware, linking them to the device and preventing unauthorized access.
Zero – Knowledge SNARK Privacy
At the core of Crescent lies the advanced cryptographic proof technique known as zero-knowledge SNARK (Zero-Knowledge Succinct Noninteractive Argument of Knowledge). This method allows one party to prove possession of information or credentials without revealing the underlying data itself.
Crescent employs the Groth16 proof system, known for its practical implementation. Groth16’s proofs are small, quick to verify, and can be shared in a single step, enhancing user privacy without extensive communication between user and verifier in the context of digital identity, particularly in unlinkability, especially regarding privacy protection, including digital identity applications, including unlinkability applications, including privacy protection applications. The system operates by establishing shared cryptographic parameters based on a credential template.
Organizations issuing similar credentials can use these parameters as long as they adhere to compatible data formats and security standards. Specialized programming tools then convert these into a Rank-1 Constraint System (R1CS), defining exactly what needs to be proven about a credential, particularly in digital identity, particularly in unlinkability, particularly in privacy protection.
To optimize real-world use, Crescent divides the proof generation into two stages: ① Prepare Stage: This preliminary step generates cryptographic values stored on the user’s device for repeated use.
② Show Stage: This quicker step utilizes stored values, randomizing them to prevent connections to previous presentations while creating a compact cryptographic summary revealing only necessary information.
Crescent digital identity verification
To demonstrate Crescent’s capabilities, a sample application was created covering two real-world scenarios: employment verification and age verification for online access. This application, composed of sample code for setting up fictional issuers and verifiers, illustrates how Crescent can be integrated into existing systems.
Setup Involves: ① Pre-generating zero-knowledge parameters for creating and verifying proofs from JSON Web Tokens and mobile driver’s licenses.
② Users obtaining a mobile driver’s license from their Department of Motor Vehicles in the context of digital identity, including unlinkability applications, including privacy protection applications, especially regarding digital identity in the context of unlinkability, particularly in privacy protection.
③ Users obtaining a proof-of – employment JSON Web Token from their employer.
④ Storing these credentials and private keys in the Crescent wallet.
Scenarios Include: ⑤ Employment Verification: Users present their employment token to an online health clinic, proving eligibility for benefits without revealing their identity.
⑥ Age Verification: Users present their driver’s license to a social network, confirming they are over 18 without disclosing their age or identity, especially regarding digital identity, including unlinkability applications, particularly in privacy protection. In both scenarios, Crescent ensures that credential presentations remain unlinkable, preventing any party from connecting them to the user.
While the sample defines its own protocol, it can be integrated into higher-level identity frameworks like OpenID/OAuth or Verifiable Credentials.
Crescent digital identities privacy
Crescent represents a significant advancement in addressing privacy concerns associated with digital identities. By implementing zero-knowledge proofs and enabling selective disclosure, Crescent empowers users to maintain control over their personal information in an increasingly digital world.
Its ability to integrate into existing systems without requiring significant changes offers a practical solution for organizations aiming to enhance privacy features, including unlinkability applications, including privacy protection applications. For those interested in exploring Crescent further, the project is available on GitHub, with recent presentations at conferences like Real-World Crypto 2025 and North Sec 2025 providing deeper insights into its functionalities. As digital identity systems continue to evolve, Crescent stands as a testament to the power of cryptographic innovations in safeguarding privacy while maintaining the convenience of digital interactions.
