My understanding was that the malformed update would allow them to bypass the 10-attempt limit and also the delays between attempts, allowing a brute force attack. Meaning a device with a sufficiently strong password would still be capable of being secure, barring any secret government technology that we don't know about that can crack 64 character random passwords(which probably does exist).

HOWEVER, if I'm not mistaken, the newer iPhones (the one in question is a 5c) hold the delay-between-attempts limit IN HARDWARE, so a firmware upgrade would do nothing. The encryption is all done in dedicated hardware on the device. Someone please correct me if I'm wrong.

Each attempt takes 80 ms. That's in hardware. There is a separate retry delay that increases exponentially then tops out at 1 hour per unsuccessful attempt. The 10-try limit is the number of consecutive unsuccessful attempts before the device erases its stored encryption keys (effectively wiping itself).

It seems that the attempt limit at least is not hardcoded and can be updated, as it has been increased in the past by an iOS update. I would suspect the same is true for the attempt retry delay time. Either way, this is only specifically applicable to devices newer than the 5c, which doesn't have a Secure Element (or "Secure Enclave" in Applespeak).

In any case, given a software image made to the FBI's specifications, the time to crack a phone depends on the complexity of the user passcode. If the user had a 4-digit numeric PIN it could be cracked in under 15 minutes. On the other hand, with a sufficiently complex passcode the expected time to brute force the device could be literally in the millions of years.

You're correct. Each attempt takes 80ms as a hardware limitation.

I'm pretty sure iOS updates are signed per device, as that's why everyone backs up their signatures for old versions (so that they can go back while Apple isn't signing them). So Apple could only sign this backdoor for one device.

http://www.saurik.com/id/12

Did you miss the part where the government said they were fine with Apple keeping the custom iOS software version in their possession, and not giving it to the government?

http://www.nytimes.com/aponline/2016/02/20/us/politics/ap-us...

"Apple may maintain custody of the software, destroy it after its purpose under the order has been served, refuse to disseminate it outside of Apple and make clear to the world that it does not apply to other devices or users without lawful court orders," the Justice Department told Judge Sheri Pym on Friday. "No one outside Apple would have access to the software required by the order unless Apple itself chose to share it."

This argument just doesn't add up to me.

Regardless of this court order, Apple already has possession of keys that can sign iOS updates to disable security features. So this "master key" already exists.

Meanwhile the government is saying that Apple can delete the tool the moment after the court order is executed, so then what is there to steal?

I just don't get the argument that this tool is any more of a "master key" than the actual "master key" Apple already has.

Monday, create a tool for phone A. Tuesday, delete the tool. Wednesday, recreate that same tool, but now for phone B. Thursday, delete the tool. Friday, recreate that same tool, but now for phone C. ...

What do you think is going to happen? Oh yeah, there's the git logs too.

This is not about one phone. It never was. It's about establishing a behavior.

Also, there's no master key. It does not exist. Apple does not have an "actual master key". Maybe Google does, but Apple has said quite clearly, that no such software or key to decrypt phones exists.

The master key they have is the ability to sign firmware updates for all phones that could disable security. The point is, it isn't a new master key. If the key was somehow lost, Apple phones would be vulnerable, just like in the dystopian hypotheticals being thrown around here.

You're thinking of this from the wrong angle. What the FBI is working to build is a legal master key to get information from modern smartphones. It's not difficult to determine this is their objective, as the director of the FBI has asked for as much from Congress.

If you didn't realize that, it's easy to see how you're caught up in the wrong argument.

This begs the question: can FBI in theory write the modified OS without Apple, and just command Apple to sign it with Apple's private key so it can be loaded without knowing the passcode and booted?

The problem is, Apple designs the software, loads it onto the device, and gives it to the government so they can do their brute force on it.

What's preventing the government from just copying the software off the device and keeping it for themselves? Obviously they'd have to do some work to make it universal, but do we really think an agency with pretty much unlimited budget, and brilliant mathematicians, couldn't get it done?

"To do some work to make it universal" = code change = thrown hash (the signature which requires the Apple key to create, and proves the software hasn't been tampered with, will be broken/no longer valid)

Cryptographic hashes like SHA and AES are designed for "dispersion" meaning, in the idea case, flipping only one bit of the input leads to a 50% probability of every single bit in the hash flipping. So while it's theoretically possible to make a change to the code, and find a way to insert that change that both (1) does the same thing and (2) hashes the same way as the original build, it's probably beyond the realm of what even a motivated attacker could do today.

The warrant allows that the phone could be entirely in Apple's possession with the FBI having only programmatic access to the PIN input. Imagine, say, an isolated SSH server with serial access to a PIN input API.

Interesting question. I don't know the answer but would be interested to hear anyone with more information weigh in.

did you miss the part where the government said they would never do this ever again?

once the precedent is set, the floodgates will open.