杨磊18

Just noticed that the selective disclosure example SIGN uses most frequently in the whitepaper proving you’re over a certain age without showing your exact birth date is actually more nuanced than the simple one line description suggests 😂
the part that surprises me:
the whitepaper presents selective disclosure as a straightforward privacy win: “prove age eligibility without revealing exact birth date.” Citizens can verify for age-gated services (alcohol, senior benefits, education programs) with minimal data exposure. Sounds clean and effective.
"But mechanically, how does it actually work? The credential still contains the full birth date. The zero-knowledge proof (ZKP) only demonstrates a mathematical statement that the birth date is before (or after) a specific threshold without ever revealing the date itself. The verifier receives cryptographic proof that the statement is true, not the underlying data.
still figuring out if…
the ZKP for age verification requires the prover to know their exact birth date while the verifier defines the age threshold. The proof shows “birth_date < (current_date - minimum_age)”. Different services set different thresholds 18 for alcohol, 65 for pensions, 16 for certain programs. This creates an interesting granularity question.
A single proof for “older than 18” already reveals more than just eligibility it narrows the possible birth date range. Add a second proof for “older than 65” or “younger than 70” from another service, and the range narrows further. Over dozens of verifications across different platforms over months and years, these overlapping range proofs can gradually reveal a much tighter window around the actual birth date.
BBS+ unlinkable credentials help prevent direct correlation of the same proof across verifiers. However, they cannot stop a single verifier or a coordinated actor from combining multiple threshold-based proofs tied to the same identity over time. This progressive leakage is a known property of range-based ZK age proofs, not unique to SIGN, yet the whitepaper presents selective disclosure as delivering strong privacy without highlighting this cumulative effect.
theres also a current_date dependency the whitepaper doesn’t mention. The ZKP needs the current date to calculate the threshold correctly, which means each proof is effectively time-stamped. That timestamp becomes part of the on-chain record.
still figuring out whether selective disclosure for age verification provides the strong privacy guarantee the whitepaper implies — or a privacy protection that degrades gradually as multiple threshold proofs accumulate across different services over a citizen’s lifetime.
And the last thing if we talk about $SIGN coin it is having better long term advantages rather then $SIREN and $BULLA

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