Gary's hacking stuff
While everyone was waiting on news for the successor of the Nintendo Switch, Nintendo released the Alarmo. A small plastic alarm clock that can wake you up with sounds from your favorite Nintendo games. While I was hesitant to buy one at first, I eventually decided to get one and look deeper into how it works.
I have a stable connection rigged up to the SWD pads on the Nintendo Alarmo. Haven't connected to my debugger board yet, but this is looking legit! pic.twitter.com/gzbkm8RGhP
Since Spinda was posting some massive progress on Twitter, I decided to contact her. She told me to take a look at the 0x70000000 range in memory. Dumping from there indeed reveals a lot of ARM instructions. This area seems to contain most of the firmware! According to the reference manual this is the so called OCTOSPI2 range. OCTOSPI is a low-level interface which is used for single/dual/quad/octal SPI communication. SPI? Is there an SPI flash on the board that I missed? There seems to be a small chip without any useful markings next to the MCU. Could that be it? After starting to reverse engineer the firmware, which I just dumped, it seems to treat the OCTOSPI range as RAM. And indeed, writing a value to an unused part of this area and resetting the system causes the value to reset back to 0x55 . After examining the OCTOSPI register configuration, this seems to be 32 MiB of HYPERRAM used for external RAM. Unfortunately this doesn't help us to defeat RDP, since we can't have a persisting payload in external RAM.
When configuring the CRYP interface, the key is placed into four 32-bit registers. Unfortunately reading out the key from those registers isn't possible, since they are write-only. Brute-forcing also isn't a viable option since there are 2128 different possible combinations. While Spinda was already looking into the contents of the eMMC (She found lots of interesting stuff, keep an eye on her Twitter!), I started talking with hexkyz about the findings. Hexkyz noticed that the CRYP interface is vulnerable to a partial overwrite attack. And indeed, since the key is split up into 4 different registers it's possible to only update 32 bits of the key and then try out all 232 different possibilities until matching output is produced by the crypto processor. This needs to be done for all four parts of the key, so we need to test for a total of 4×232 different combinations, which is possible to do in a few hours. After writing a small payload to perform this, I let it run overnight. The next morning I checked the progress and it was done, I had successfully obtained the AES-128-CTR key used to encrypt and decrypt the Alarmo content files.
