ANONYMOUS CREDENTIALS: AN ILLUSTRATED PRIMER

Summary from the TLDR InfoSec newsletter

As age-verification laws spread across 25 states in the US and over a dozen countries, anonymous credential systems built on blind signatures and zero-knowledge proofs offer a cryptographic path to proving attributes such as age or residency without exposing the underlying identity to issuers or relying parties. The core challenge is preventing credential cloning: single-use Chaumian credentials bound to blind-signed serial numbers address this but require per-session issuance, while ZK-based reusable credentials solve efficiency and expressiveness at the cost of requiring N-time use limits enforced via PRF-derived serial numbers or hardware binding. Security practitioners building identity systems should treat the issuer-resource collusion threat model as a first-class design requirement rather than an afterthought.