{"id":70184,"date":"2016-02-22T12:31:57","date_gmt":"2016-02-22T12:31:57","guid":{"rendered":"https:\/\/www.transcend.org\/tms\/?p=70184"},"modified":"2016-02-22T12:31:57","modified_gmt":"2016-02-22T12:31:57","slug":"upgrade-your-iphone-passcode-to-defeat-the-fbis-backdoor-strategy","status":"publish","type":"post","link":"https:\/\/www.transcend.org\/tms\/2016\/02\/upgrade-your-iphone-passcode-to-defeat-the-fbis-backdoor-strategy\/","title":{"rendered":"Upgrade Your iPhone Passcode to Defeat the FBI\u2019s Backdoor Strategy"},"content":{"rendered":"

\"Exterior<\/a>
\n18 Feb 2016 – <\/em>Yesterday, apple CEO Tim Cook published an open letter<\/a>\u00a0opposing\u00a0a court order to build the FBI a \u201cbackdoor\u201d for the iPhone.<\/p>\n

Cook\u00a0wrote\u00a0that the backdoor, which removes limitations on how often an attacker can incorrectly guess an iPhone passcode, would set a dangerous precedent and \u201cwould have the potential to unlock any iPhone in someone\u2019s physical possession,\u201d even though in this instance, the FBI is seeking to unlock a single iPhone belonging to one of the\u00a0killers\u00a0in a 14-victim mass shooting spree in San Bernardino, California, in December.<\/p>\n

It\u2019s true that ordering Apple to develop\u00a0the backdoor\u00a0will fundamentally undermine\u00a0iPhone security, as Cook and other digital security\u00a0advocates\u00a0have argued<\/a>. But it\u2019s possible for individual iPhone users to protect themselves from government snooping by setting\u00a0strong passcodes on their phones \u2014 passcodes the FBI would not be able to unlock even if it gets its\u00a0iPhone backdoor.<\/p>\n

The technical details of how the iPhone encrypts data, and how the FBI might circumvent this protection, are complex and convoluted, and are being thoroughly explored elsewhere on the internet. What I\u2019m going to focus on here is how ordinary iPhone users can protect themselves.<\/p>\n

The short version: If you\u2019re worried about governments trying to access your phone, set your iPhone up with\u00a0a random, 11-digit numeric passcode. What follows is an explanation of\u00a0why that will protect you and how to actually do it.<\/p>\n

If it sounds outlandish to worry\u00a0about government agents\u00a0trying to crack into your phone,\u00a0consider that\u00a0when you travel internationally, agents at the\u00a0airport or other border crossings\u00a0can seize, search, and temporarily retain your digital devices \u2014\u00a0even without any grounds for suspicion<\/a>. And while a local police officer can\u2019t search your iPhone without a warrant, cops have used their own digital devices to get search warrants within 15 minutes, as\u00a0a\u00a0Supreme Court opinion recently noted<\/a>.<\/p>\n

The most obvious way to try and crack into your iPhone, and what the FBI is trying to do in the San Bernardino case, is to simply run through every possible passcode until the correct one is discovered and the phone is unlocked. This is known as a \u201cbrute force\u201d attack.<\/p>\n

For example, let\u2019s say you set a six-digit passcode on your iPhone.\u00a0There are 10 possibilities for each digit\u00a0in a numbers-based passcode, and so there are\u00a0106<\/sup>, or 1 million, possible combinations for a six-digit passcode as a whole. It is trivial for a computer to generate all\u00a0of these possible codes. The difficulty comes in trying to test them.<\/p>\n

One obstacle to testing all possible\u00a0passcodes is that the iPhone intentionally slows down after you guess wrong a few times. An\u00a0attacker can\u00a0try four incorrect\u00a0passcodes before she\u2019s forced to wait one minute. If she continues to guess wrong, the time delay increases to five minutes, 15\u00a0minutes, and finally one hour. There\u2019s even a setting to erase all data on the iPhone after 10\u00a0wrong guesses.<\/p>\n

This is where the FBI\u2019s requested backdoor comes into play. The FBI is demanding that Apple create a special version of the iPhone\u2019s operating system, iOS, that removes the time delays and ignores the\u00a0data erasure setting. The\u00a0FBI\u00a0could\u00a0install this malicious software\u00a0on the\u00a0San Bernardino killer\u2019s\u00a0iPhone, brute force the passcode, unlock the phone, and access all of its data. And that process could hypothetically be repeated on anyone else\u2019s iPhone.<\/p>\n

(There\u2019s also speculation<\/a>\u00a0that\u00a0the government could make Apple alter the operation of a piece of iPhone hardware known as the Secure Enclave; for the purposes of this article, I assume the protections offered by this hardware, which would slow an attacker down even more, are not in place.)<\/p>\n

Even if the FBI gets its way and can clear away iPhone safeguards against passcode guessing, it faces another obstacle, one that should help keep it from cracking passcodes of, say, 11 digits: It can only test\u00a0potential\u00a0passcodes for your iPhone using\u00a0the\u00a0iPhone itself; the FBI can\u2019t use a supercomputer or a cluster of iPhones to speed up the guessing\u00a0process. That\u2019s because\u00a0iPhone models,\u00a0at least as far back as May 2012<\/a>, have come with a\u00a0Unique ID (UID) embedded in the device hardware. Each iPhone has a different UID fused to the phone, and, by design, no one can read it and copy it to another computer. The iPhone can only be unlocked when the owner\u2019s passcode is combined with the the\u00a0UID\u00a0to derive an\u00a0encryption key.<\/p>\n

So the FBI is stuck using your iPhone to test passcodes. And it turns out that your iPhone is kind of slow at that: iPhones intentionally encrypt data in such a way that they must spend about\u00a080 milliseconds doing the math needed to test a passcode, according to Apple<\/a>. That limits them to testing\u00a012.5 passcode guesses per second, which means\u00a0that guessing a six-digit passcode would take, at most, just over 22 hours.<\/p>\n

You can calculate the time for that task\u00a0simply by dividing the 1 million possible six-digit passcodes by 12.5 per seconds.\u00a0That\u2019s 80,000 seconds, or 1,333 minutes, or 22 hours. But the attacker doesn\u2019t have to try each passcode; she can stop when she finds one that successfully unlocks the device. On average, it will only take 11 hours for that to happen.<\/p>\n

But the FBI would be happy to spend\u00a0mere\u00a0hours cracking your iPhone. What if you use a longer passcode? Here\u2019s how long the FBI would need:<\/p>\n