200 milliseconds to check you. 3,170 years to prove you're new.

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Checking this man's fingerprint takes under 200 milliseconds. Proving he isn't already enrolled? 3,170 years. For each day of enrolment.

A ration shop. He puts his thumb on a scanner, with his Aadhaar number. The number points to one record. One comparison, under 200 milliseconds. The answer is a signed yes or no. But when he first enrolled, he had no number. So you must search everyone on file. One-to-N.

How big is that search? A billion people, ten fingers each. Enrol a million a day, as in 2014. That's 10 quadrillion comparisons. At 100,000 matches a second? About 3,170 years. For one day's enrolments.

So Aadhaar splits them. Enrolment goes down a slow, wide path. Indexed, massively parallel, asynchronous. Minutes to days. Authentication goes down a fast, narrow path. One read, one match. A backlog on one never slows the other.

Enrolment end to end? 3 to 90 days. And that's fine. Nobody is waiting at a counter.

Two questions that sound alike. Treating them the same is the mistake. Authentication is a lookup. Deduplication is a search.

Full breakdown in the lecture.