In the older versions of iOS, Siri was accessible from the lock screen which was a great security lapse for the user,
because anyone could access personal data like pics using Siri. Moreover, after unlocking the device, Siri can answer whatever you want to ask and will respond to you at your every command. In other words, Siri responds to the speech itself, not the speaker.
Apple thought it as a flaw and been working on it lately for the betterment of Siri. Finally, Apple thinks of a solution to this problem. In the upcoming update of iOS, Siri might get updated and may use different combinations of phrases and your unique pronunciation/voice. This will ensure that Siri answers to you and only you.
After coming up with this solution to the problem, Apple has now filed to patent this tech.
Up until now when a digital assistant has been invoked with a voice command, the digital assistant is responsive to the speech itself, not to the speaker. Consequently, a user other than the owner of the electronic device is able to utilize the digital assistant, which may not be desirable in all circumstances […]
Apple’s invention provides a method to train Siri to know the voice of the owner of the iDevice before responding to a command.
In this new approach, the device will ask the user for a specific word or phrase that will be used as Siri access code instead of “hey Siri”. Your device would store authentication in both ways i.e some phrase and your voice as well. You’ll only get access to Siri if your combination is correct.
If the voice doesn’t match the stored pattern for some reasons, the device will ask to use TouchID or enter the passcode for authentication.
This new approach looks like a bit difficult as the differentiation b/w individual voice for reliability may take a while. This approach is already being used by Commercial Verification Security Systems like Telephone Banking Services. The phrase used for identification will be known phrase such as your Date of Birth that will help a lot system to reliability identify your voice.
While the Apple has applied for this new tech for the digital assistant, we cannot say for sure if it would see the light of the day.