San Francisco, Sep 14 A day after Apple announced facial recognition system to unlock iPhone X, a US senator has written a letter to CEO Tim Cook, conveying concerns on users' privacy and security. According to a report in appleinsider.com on Thursday, Senator Al Franken (Democrat-Minnesota) has asked several questions related to Apple's implementation of Face ID technology. "While details on the device and its reliance on facial recognition technology are still emerging, I am encouraged by the steps that Apple states it has taken to implement the system responsibly," Franken wrote. "However, substantial questions remain about how Face ID will impact iPhone users' privacy and security, and whether the technology will perform equally well on different groups of people," the letter further read. According to Apple, Face ID is more secure than Touch ID fingerprint technology. There's a one in a million chance someone else's face will fool Face ID. Franken, who is the member of the Senate Judiciary Subcommittee on Privacy, Technology and the Law, asked Cook to provide more clarity on the Face ID system. "To offer clarity to the millions of Americans who use your products, I ask that you provide more information on how the company has processed these issues internally, as well as any additional steps that it intends to take to protect its users," the Senator wrote. Face ID uses 'TrueDepth' camera system made up of a dot projector, infrared camera and flood illuminator, and is powered by A11 Bionic to accurately map and recognise a face. Face ID projects more than 30,000 invisible IR dots. The IR image and dot pattern are pushed through neural networks to create a mathematical model of your face and send the data to the secure enclave to confirm a match, while adapting to physical changes in appearance over time. Franken, however, asked whether Face ID "faceprint" data is stored onboard iPhone X, if this information can be extracted from the device and whether Apple plans to store the data on offsite servers. Apple had said in its press release: "All saved facial information is protected by the secure enclave to keep data extremely secure, while all of the processing is done on-device and not in the cloud to protect user privacy". Franken has also asked Cook how Apple would respond to law enforcement requests to access 'faceprint' data or the Face ID system itself. Apple has always been reluctant to let enforcement agencies get into its hardware security technology. Last year, Apple refused to comply with a court order after federal prosecutors tried to unlocked an iPhone tied to a 2015 terrorist attack in San Bernardino, California. Franken wants Cook to reply to his concerns by October 13.