Why Aadhaar tells a bank only yes or no

transcript

Tell a bank how close the fingerprint matched? You just helped a forger. That's why Aadhaar only ever says yes or no.

The bank asks: is this him? Why not send back a match score? The bank picks its own threshold. Sounds flexible. But every caller learns that score. Including attackers. Or send the stored template, to match locally? It leaks through every agency.

Here's the attack. Submit a fake fingerprint. Read the score. Did it get closer? Keep the tweak that helped. Again. And again. Every answer points the way. That's hill-climbing.

So the scanner encrypts the print with UIDAI's public key. At the sensor. The bank and the agencies only ever carry ciphertext. Only CIDR's HSM can decrypt it. Then one one-to-one match. The answer: a signed yes or no. A transaction ID. A timestamp.

No score to climb. No fingerprint to leak. No personal data, unless he consents to e-KYC.

And the scanner's key is public. A public key can't decrypt. Return a bit, not data. Then there's nothing to leak.

Full breakdown in the lecture.