8 ms·
How do you brute force the PIN if the KDF process operates over the PIN, plus a 256-bit UID that's only accessible to signed code running on the SoC? If you mo
by teacup50 11y ago
How do you brute force the PIN if the KDF process operates over the PIN, plus a 256-bit UID that's only accessible to signed code running on the SoC?
If you modify the kernel on the NAND, signature checks in the on-die bootloader will fail, and you won't get to run.
If you modify application binaries on the NAND, signature checks in the signed kernel will fail, and you won't get to run.
- lisper 11y agoTurn on the device. Make 5 PIN guesses. Replace the flash chip with a copy of the original. Reboot the device. Make 5 more guesses.
- teacup50 11y agoIn other words, introduce a much, much longer iteration delay that makes the entire effort pointless, while risking destroying the device and all data on it by desoldering the (presumably BGA) NAND?
- lisper 11y agoYou wouldn't solder the chip in every time, you'd install a ZIF socket.
- extrapickles 11y agoDue to the high density, a socket will not fit without a making a pigtail to fit onto the board (commonly available sockets are fairly big). The flash in question is a BGA part on a high density double sided board. It definitely would be hard to desolder the flash without desoldering anything else nearby (as a bonus, the CPU is directly on the other side of the PCB). Specialized machines exist for doing this, but require a highly skilled operator. They want something they can plug the phone into so they can give every site one and not send it out to a expensive technician for modification and data extraction.
- tzs 11y agoHmmm....the flash and the CPU are opposite each other? Interesting. I wonder if that was done on purpose to make it harder to mess with things, or they just ended up that way because it made the layout and routing simpler? If they were not opposite each other, then the following approaches to spying on or tampering with the system would be possible: • Cut the write signal between the CPU and the flash so that the CPU cannot erase anything in the flash. • Cut all the control, data, and address lines between the CPU and the flash and insert a man-in-the-middle device that can allow or block CPU access to the flash and that can read/write the flash itself.
- lisper 11y ago> Specialized machines exist for doing this, but require a highly skilled operator. That's true. But come on, this is the FBI we're talking about. > They want something they can plug the phone into so they can give every site one and not send it out to a expensive technician for modification and data extraction. Yes, of course that is what they want. That is the whole point.
- Someone1234 11y agoThat sounds time consuming. 5,040 possible pins with the 4x length pin and 151,200 possible pins with the 6x length pin.
- lisper 11y agoI don't know how long it takes a 5C to boot, but my iPod takes 30 seconds. Add another 30 seconds to swap out the RAM chip (I'm assuming a ZIF socket has been installed) and you can brute-force 150k PINs in 30k minutes which is about 3 weeks.
- w23j 11y agoHow do you get these numbers? Aren't the number of possible pins 10^4 = 10,000 and 10^6 = 1,000,000?