549
edits
Changes
Jump to navigation
Jump to search
Line 175:
Line 175: + + Line 234:
Line 236: − + − Unless noted otherwise, all keyslots on retail units use the hardware key-scrambler, where the final normal-key is generated in hardware using the input keyX and keyY. This normal-key is then written to the hardware keyslot by the AES engine, all of the AES engine key registers are write-only. The internal normal-key keyslot is only updated when the keyY is written to, the keyslot's normal-key is not immediately updated when writing to the keyX.+ + + + + + + − + − After writing to a keyslot when the keyslot is already selected, the keyslot must be re-selected for the updated keyslot key-data to be used.+ − Writing to the key FIFOs with byte writes results in the AES engine converting the byte to a word for setting the key word, with this: word = (byteval) | (byteval<<8) | (byteval<<16) | (byteval<<24). The result is the same regardless of which FIFO register byte was written to.+
Clarified keyslots
== Keyslots ==
== Keyslots ==
There are 0x40 keyslots, each of which stores three keys called keyX, keyY and normalkey. All keys can be set explicitly, but the normalkey can optionally be generated using a hardware key scrambler instead (see below). There is no way to read the contents of a keyslot.
{| class="wikitable" border="1"
{| class="wikitable" border="1"
! Keyslot
! Keyslot
|}
|}
=== Hardware key generator ===
=== Updating keydata ===
When bit26 in REG_AESCNT is enabled, keyslots can be updated by selecting a particular keyslot using REG_AESKEYCNT and then consecutively writing four words to REG_AESKEYXFIFO (keyX), REG_AESKEYYFIFO(keyY), or REG_AESKEYFIFO (normalkey).
After writing to a keyslot, the keyslot in REG_AESKEYCNT must be set again, even when writing to the same keyslot.
Writing to the key FIFOs with byte writes results in the AES engine converting the byte to a word for setting the key word, with this: word = (byteval) | (byteval<<8) | (byteval<<16) | (byteval<<24). The result is the same regardless of which FIFO register byte was written to.
The TWL keyslots 0x00-0x03 can be set directly by writing to the REG_AESKEY0-REG_AESKEY3 registers.
=== keyX ===
=== keyX ===
The ARM9 bootrom initializes the keyX for each 3DS keyslot, the ARM9 bootrom also initializes the keyY for the keyslots where NATIVE_FIRM doesn't set the keyY. In certain cases Process9 may also set the keyX.
The ARM9 bootrom initializes the keyX for each 3DS keyslot, the ARM9 bootrom also initializes the keyY for the keyslots where NATIVE_FIRM doesn't set the keyY. In certain cases Process9 may also set the keyX.
=== Updating keydata ===
=== Hardware key generator ===
A dedicated hardware key generator can be used to generate a keyslot's normalkey from its keyX and keyY by enabling the corresponding bit in REG_AESKEYCNT. If enabled, the hardware key generator is triggered by writing the keyY (which also seems to be the only way to trigger it). The algorithm used for key generation is unknown.
Unless noted otherwise, all keyslots on retail units use the hardware key-scrambler.
=== FIRM-launch key clearing ===
=== FIRM-launch key clearing ===
Starting with [[9.0.0-20]] the Process9 FIRM-launch code now "clears" the following AES keyslots, with certain keydata by writing the normal-key: 0x15 and 0x18-0x20. These are the keyslots used by the New3DS [[FIRM]] arm9bin loader(minus keyslot 0x11), so the New3DS Process9 presumably does this too.
Starting with [[9.0.0-20]] the Process9 FIRM-launch code now "clears" the following AES keyslots, with certain keydata by writing the normal-key: 0x15 and 0x18-0x20. These are the keyslots used by the New3DS [[FIRM]] arm9bin loader(minus keyslot 0x11), so the New3DS Process9 presumably does this too.