The Unique Identification Authority of India (UIDAI), the Aadhaar-issuing body, on Tuesday told the Supreme Court that it cannot provide authentication failure rates at the state level but it stood at 8.54% at the national level in cases of iris scan and 6% in those concerning fingerprint scan. However, it told a five-judge Constitution bench led by Chief Justice Dipak Misra that \u201cauthentication failures do not mean exclusion or denial from subsidies, benefits or services since the Requesting Entities are obliged under the law to provide for exception handling mechanisms\u201d. It further said that a person\u2019s mobile number can be used for authentication where both iris and fingerprint scan could not be used. While responding to a set of questions raised by the petitioners on its presentation on the technical and security aspects of Aadhaar, UIDAI chief operating officer Ajay Bhushan Pandey said biometric authentication is based on l:1 matching and, therefore, in that sense it is not probabilistic. \u201cIf biometrics are captured well it will lead to successful authentication. If biometrics are not well captured during authentication or an impostor tries authentication, it will lead to authentication failure. Aadhaar Proof of Concept studies show that a vast majority of residents (> 98%) can successfully authenticate using biometric modalities such as fingerprints and\/or iris,\u201d he clarified. The bench is hearing around 30 petitions challenging several aspects of the Aadhaar scheme, including the validity of Aadhaar and possible leakage of data, making Aadhaar mandatory for social welfare benefits, filing income tax returns (ITRs) as well as for obtaining and retaining PAN, the mandatory parting of biometric details like iris scans and fingerprints, thus alleging violation of the citizens\u2019 right to privacy. Besides, two other petitions challenging Aadhaar \u2014 one by the West Bengal government on the mandatory linking of Aadhaar to various schemes and another challenging its mandatory linking with mobile numbers \u2014are also being heard. The petitions also include one by former Karnataka High Court judge Justice KS Puttuswamy challenging the validity of the Aadhaar Act on the ground it violated the fundamental right to privacy. Earlier, the Supreme Court had passed a slew of orders asking the government and its agencies not to make Aadhaar mandatory for extending benefits of their welfare schemes, but had allowed the government to use unique ID for a large number of purposes like welfare schemes and income tax return filing, with a rider that it would not be made mandatory.