India's vaunted tech savvy is being put to the test this week as the country embarks on a daunting mission: assigning a unique 12-digit number to each of its 1.2 billion people.

The project, which seeks to collect fingerprint and iris scans from all residents and store them in a massive central database of unique IDs, is considered by many specialists the most technologically and logistically complex national identification effort ever attempted. To pull it off, India has recruited tech gurus of Indian origin from around the...