EncryptionPasswords, privacy and protection: can Apple meet FBI’s demand without creating a ‘backdoor’?

By H. V. Jagadish

Published 24 February 2016

The point of encryption is to make decryption hard. However, hard does not mean impossible. The FBI could decrypt this data, with sufficient effort and computational power, and they could do this with no help from Apple. However, this route would be expensive, and would take some time. In effect, what they’re requesting of Apple is to make their job easier, cheaper and faster. Ultimately, how this matter gets resolved may depend more on the big-picture question of what privacy rights we as a society want for the data we record on our personal devices. Understanding the technical questions can inform this discussion.

The San Bernardino terrorist suspect Syed Rizwan Farook used an iPhone 5c, which is now in the possession of the FBI. The iPhone is locked. The FBI wants Apple to help unlock it, presumably so they can glean additional evidence or information about other possible attacks. Apple has declined, and appears to ready to defy a court order. Its response is due February 26. So what’s the technology they’re fighting over?

The code to unlock the phone is known only to Farook, who is dead, and any confidants he may have shared it with. Even if he were alive, it would probably be difficult to get him to reveal it.

But phones are typically locked with a very simple personal identification number (PIN) of only four to six digits. That means, at most, there are a million possible PIN values. It’s straightforward to write a computer program that would methodically walk through all these possible values, trying each in turn until the correct one is found. Indeed, there even are products on the market that will do just this. Given that modern computers can execute over one billion instructions every second, even a conservative estimate says testing all one million PIN possibilities would take only about a second.

Ways to ward off attack
One way to defend against this kind of break-in attempt is to do something drastic after multiple failures. For example, Apple deletes all data on the iPhone after ten incorrect unlocking attempts in succession, if the user has turned on this feature. We don’t know if this defense is activated on Farook’s phone – but the FBI doesn’t want to gamble that it isn’t, turn out to be wrong, and watch the phone be wiped clean after 10 incorrect guesses.

A second approach is to force a delay after each failed attempt. If the real authorized user accidentally types in the wrong code, she won’t mind waiting sixty seconds before the phone will let her try again. But for a computer that wants to try a million possibilities, the time required to try all possibilities has gone up by a factor of a million or more.

The FBI, of course, should have no difficulty programming a computer to try all possible passwords. It simply wants Apple to turn off the defenses.