India's highest court has upheld the legality of the nation's controversial biometric identity database, saying it does not violate citizens' rights to privacy.

Key points: Indian residents cannot receive welfare food rations, other benefits without being entered into Aadhaar

Indian residents cannot receive welfare food rations, other benefits without being entered into Aadhaar There is concern the system is vulnerable to security breaches

There is concern the system is vulnerable to security breaches An Indian newspaper has already bought access to data by paying hackers about $10

More than 1 billion people are already enrolled in the database, Aadhaar.

All residents of India are compelled to hand over their personal details to the giant database, including their iris scans and fingerprints, if they want basic services.

Residents cannot receive welfare food rations without being entered into the system.

Sorry, this video has expired The world's largest biometric identity database approved in India

Aadhaar was launched in 2010 as a voluntary system designed to tackle welfare fraud but was expanded to be linked to almost every aspect of daily life, including getting a mobile number, bank account or passport.

Shyam Divan, a lawyer arguing against making the system mandatory, said Aadhaar "alters the relationship between the citizen and the state".

A woman waits her turn to enrol in Aadhaar. ( Reuters: Saumya Khandelwal )

"It seeks to tether every resident of India to an electronic leash," Mr Divan said.

"This leash is connected to a central database that's designed to track transactions across the life of the citizen.

"This record will enable the state to profile citizens, track their movements, assess their habits and silently influence their behaviour."

Critics say Aadhaar could be used over time to profile people and influence political behaviour.

Lawyers argue that if a person's profile in the database is disabled or revoked, he or she could be immediately deprived of basic services like a phone number, bank account, education or food.

There is also concern that the system is extremely vulnerable to security breaches.

Earlier this year, an Indian newspaper was able to buy access to the personal data of any of the one billion people in the system by paying hackers about $10.

Instead of investigating the breach, the Indian Government initially responded by filing criminal charges against the newspaper.

There is concern that Aadhaar is extremely vulnerable to security breaches. ( Reuters: Saumya Khandelwal )

There is also criticism that India's poorest are suffering under the scheme.

There are reports of people's fingerprints not being accessible in rural areas with poor internet connectivity, leading to them being denied food rations.

The ruling by India's Supreme Court did however limit the scope of the biometric system.

Until today, Indian residents have had to link their private bank accounts, mobile numbers and even school admissions to their profile in the government database.

The court ruled those regulations are unconstitutional, although it is too late for the hundreds of millions who have already linked such accounts to the government database.