The Apple boss said the FBI was planning to force Apple to build so-called backdoors - equivalent to a digital master key - into the iPhone using the All Writs Act of 1789, something Cook said the company was not willing to do.
"We have great respect for the professionals at the FBI, and we believe their intentions are good. Up to this point, we have done everything that is both within our power and within the law to help them," Cook wrote on the Apple website.
"But now the US government has asked us for something we simply do not have, and something we consider too dangerous to create. They have asked us to build a backdoor to the iPhone."
Cook argued that building a backdoor would be too dangerous as it would allow criminals to develop tools that unlock any iPhone in their possession.
The CEO's open letter helps position the firm as the leader of pro-encryption and it has been praised by those in the data security, development and technology fields on social media:
I wonder what it was like to be in the room during drafting of https://t.co/042rAcPxNQ -- how much legal, PR, product etc vs. just Tim Cook.— Ryan Lackey (@octal) February 17, 2016
Incredibly powerful and clear response from Apple, signed by Tim Cook https://t.co/wzBLBWxC2z— Rachel Bremer (@ryb) February 17, 2016
Tim Cook absolutely sticks it to the FBI https://t.co/PXFbeUw2Pr— Jonathan Haynes (@JonathanHaynes) February 17, 2016
damn that Tim Cook letter is real good. Can't imagine too many other technology companies taking up this fight either— Rupert H (@rpy) February 17, 2016
Remarkable letter from Tim Cook on the importance of encryption & the US govt's demand for a backdoor to the iPhone: https://t.co/AvTRxReiw5— Nicholas Dawes (@NicDawes) February 17, 2016