The encryption itself isn’t what the FBI is worried about. They can brute force encrypted data. The item that’s been perplexing them it the “Mission Impossible” hardware that erases the data after 10 wrong guesses.
It's both. The data on the Flash drive is encrypted to a far higher standard than the simplistic unlocking passcode. They can't brute force the data on the Flash drive. . . even using the lowest possible size key of 132 characters (Apple permits all 223 characters of the Apple character set to be used), and the fastest available supercomputer sped up by three times which can try 10 trillion keys per year, it would take 5.62 X 10195 years to brute force every possible key!
That is effectively impossible. Why? Consider these facts. Cosmologists will tell you that looking out as far as we can see into the Universe, some 16 billion light years, with all the galaxies with all their stars, planets, and the gas in-between them, of all we can see, everything is made up of approximately 4.75 X 1084 ATOMS . . . and everyone of those atoms will have decayed completely into quarks, leptons, or bosons by approximately 7.84 X 1080 years have elapsed. . . in other words, the Universe dies of heat death in less than 40% of the time required to test all of the possible minimum size keys to just one iPhone's encryption.
There’s more to this than is being listed here.
First, the setting on the phone in question might have the “erase in 10 failed attempts” turned on....or it might be off! The FBI is afraid to attempt the unlock by brute force for fear the setting is on, and the data would be wiped. But who knows, maybe they could run through all the numbers in a few weeks or months and no erase would happen. Also, remember, once they find it, they stop the hunt, so maybe after only a couple thousand attempts it is found, and won’t be the final available choice requiring all numbers to be tried!
Second, people are assuming a 4-digit unlock code. However, the unlock code can be customized and can be a 4-digit numeric (10,000 combos), a 6-digit numeric (1 million combos), a custom numeric code (up to 11 digits), or a custom alphanumeric code (with numbers, letters, and special characters, and can be at least 50 characters, and some say can be more than 90 characters before receiving a warning that that’s too many).
Third, the iphone increases the time required to wait for a repeat unlock attempt after failed attempts! One source says that beginning with the 5th failed attempt, there is a 1 minute wait before the 6th attempt can be entered (and not the nanoseconds a supercompter could use to enter the next number and then next and the next, etc.). The 7th attempt requires a 5 minute wait, the 8th requires 15 minutes, and the 9th and subsequent tries require 60 minute waits between attempts!!!! That will really add to the time required to brute force find the unlock code, assuming it doesn’t go black and wipe the memory at the failed 10th attempt.
Just interesting additional info on this. No wonder the FBI wants Apple to do it for them!