Why does presenting my credential to ten verifiers let them silently map my life?
Opportunity
Every SD-JWT credential, the dominant format being deployed in EUDI Wallets across EU member states in 2026, carries a single issuer signature that is identical across all presentations. Any two verifiers who receive the same credential can share that token and link both visits to the same person. BBS+ with randomizable signatures prevents this correlation, but it is computationally heavier and production wallet support is thin. An IEEE EuroS&P 2026 paper confirms that issuer-verifier unlinkability is structurally impossible in salted-hash selective disclosure schemes like SD-JWT without issuing fresh credential batches per presentation, an operational burden no major deployment has solved. The hundreds of millions of wallets rolling out under eIDAS 2.0 today will silently correlate holders across every verifier they interact with for the lifetime of the credential.
Why it matters
Unlinkable presentation is the primitive that makes selective disclosure mean privacy rather than just granularity, and the dominant deployed format cannot provide it.
How I score the opportunity
The Opportunity Score is my own read, not a measurement: how much it hurts, how often it bites, and how little exists to solve it today. Higher means I think it is more worth building.
How much pain it causes when it shows up.
How often people actually run into it.
How little good tooling exists for it today.
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