BCT (Boot Configuration Table) is a data structure present on Tegra based devices that supplies boot time configuration parameters.
The Switch's BCT is included in the firmware package titles (0100000000000819 and 010000000000081A) and is installed into eMMC storage's boot partition 0. A total of four BCT copies can be installed into the system: normal, normal backup, safe mode and safe mode backup.
The Erista BCT's data is only signed after offset 0x510. Therefore, regions like CustomerData can be freely modified without resigning. This is done by NS when injecting a new keyblob during a system update, for example.
The Mariko BCT's data is signed starting at offset 0x420 and encrypted starting at offset 0x480, so the keyblob system is no longer used.
During boot, the boot ROM parses the appropriate BCT from eMMC storage and stores a copy of it in IRAM.
Format
Erista
| Offset | Size | Field | Description |
|---|---|---|---|
| 0x0 | 0x210 | BadBlockTable | Table containing information on bad blocks
0x0: EntriesUsed (0x200) 0x4: VirtualBlockSizeLog2 (0xF) 0x5: BlockSizeLog2 (0xE) 0x6: BadBlocks 0x206: Reserved |
| 0x210 | 0x100 | Key | BCT RSA public key's modulus |
| 0x310 | 0x110 | Signature | BCT cryptographic signature
0x310: CryptoHash (empty) 0x320: RsaPssSig |
| 0x420 | 0x4 | SecProvisioningKeyNumInsecure | Used for Factory Secure Provisioning (always 0) |
| 0x424 | 0x20 | SecProvisioningKey | Used for Factory Secure Provisioning (always 0) |
| 0x0444 | 0xC4 | CustomerData | Data block available for the customer (used in key generation)
0x444: Reserved 0x450: Keyblob 0x500: Reserved |
| 0x508 | 0x4 | OdmData | Empty |
| 0x50C | 0x4 | Reserved | Empty |
| 0x510 | 0x10 | RandomAesBlock | Empty |
| 0x520 | 0x10 | UniqueChipId | Empty |
| 0x530 | 0x4 | BootDataVersion | Set to 0x210001 (BOOTDATA_VERSION_T210) |
| 0x534 | 0x4 | BlockSizeLog2 | Always 0xE |
| 0x538 | 0x4 | PageSizeLog2 | Always 0x9 |
| 0x53C | 0x4 | PartitionSize | Always 0x1000000 |
| 0x540 | 0x4 | NumParamSets | Number of device parameter sets (always 0x1) |
| 0x544 | 0x4 | DevType | Device type (0x4 == Sdmmc) |
| 0x548 | 0x40 | DevParams | Device parameters
0x548: ClockDivider (0x9 == 24MHz) 0x54C: DataWidth (0x2 == 8Bit) |
| 0x588 | 0x4 | NumSdramSets | Number of SDRAM parameter sets (always set to 0, but parameters are used despite this) |
| 0x58C | 0x768 | SdramParams0 | Default values filled in |
| 0xCF4 | 0x768 | SdramParams1 | Default values filled in |
| 0x145C | 0x768 | SdramParams2 | Default values filled in |
| 0x1BC4 | 0x768 | SdramParams3 | Default values filled in |
| 0x232C | 0x4 | BootLoadersUsed | Number of bootloaders installed (always 0x2, maximum is 0x4) |
| 0x2330 | 0x12C | BootLoader0 | Configuration parameters for bootloader 0 (main)
0x2330: Version (variable) 0x2334: StartBlock (0x40 for BootImagePackage, 0x100 for BootImagePackageSafe) 0x2338: StartPage (0) 0x233C: Length (variable) 0x2340: LoadAddress (0x40010000) 0x2344: EntryPoint (0x40010020 for 1.0.0-3.0.2, 0x40010040 for 4.0.0+) 0x2348: Attribute (0 for BootImagePackage, 1 for BootImagePackageSafe) 0x234C: CryptoHash (empty) 0x235C: RsaPssSig |
| 0x245C | 0x12C | BootLoader1 | Configuration parameters for bootloader 1 (backup)
0x245C: Version (variable) 0x2460: StartBlock (0x50 for BootImagePackage, 0x110 for BootImagePackageSafe) 0x2464: StartPage (0) 0x2468: Length (variable) 0x246C: LoadAddress (0x40010000) 0x2470: EntryPoint (0x40010020 for 1.0.0-3.0.2, 0x40010040 for 4.0.0+) 0x2474: Attribute (0 for BootImagePackage, 1 for BootImagePackageSafe) 0x2478: CryptoHash (empty) 0x2488: RsaPssSig |
| 0x2588 | 0x12C | BootLoader2 | Reserved space for bootloader 2 (unused) |
| 0x26B4 | 0x12C | BootLoader3 | Reserved space for bootloader 3 (unused) |
| 0x27E0 | 0x1 | EnableFailBack | Always 0 |
| 0x27E1 | 0x4 | SecureJtagControl | Always 0 |
| 0x27E5 | 0x4 | SecProvisioningKeyNumSecure | Used for Factory Secure Provisioning (always 0) |
| 0x27E9 | 0x12 | Reserved | Always starts with 0x80000000 (NVBOOT padding pattern) |
| 0x27FB | 0x5 | Padding | Empty |
CustomerData
This data block is ignored by the boot ROM, therefore is available for the programmer to use freely. The Switch uses 0xB0 bytes of this area, at offset 0x0450, to store the active keyblob. All remaining bytes are zero.
The first bootloader validates and decrypts this block for further key generation. The decrypted keyblob payload is as follows.
| Offset | Size | Description |
|---|---|---|
| 0x0 | 0x80 | Array of master static key encryption keys |
| 0x80 | 0x10 | PK11 key |
BootLoader0
The version field controls which keyblob is used, where 0x1 is the first one. See Cryptosystem for the keyblobs used by each system-version.
Mariko
| Offset | Size | Field | Description |
|---|---|---|---|
| 0x0 | 0x210 | Pcp | BCT public cryptographic parameters
0x0: KeySize 0x4: Reserved 0x10: PublicKeyModulus 0x110: PublicKeyExponent |
| 0x210 | 0x110 | Signature | BCT cryptographic signature
0x210: CryptoHash (empty) 0x220: RsaPssSig |
| 0x320 | 0x20 | SecProvisioningKey | Used for Factory Secure Provisioning (always 0) |
| 0x340 | 0x4 | SecProvisioningKeyNumInsecure | Used for Factory Secure Provisioning (always 0) |
| 0x344 | 0xC | Padding | Empty |
| 0x350 | 0xD0 | CustomerData | Data block available for the customer |
| 0x420 | 0x10 | RandomAesBlock | |
| 0x430 | 0x10 | Empty | |
| 0x440 | 0x40 | Empty | |
| 0x480 | 0x10 | RandomAesBlock2 | |
| 0x490 | 0x10 | UniqueChipId | Empty |
| 0x4A0 | 0x4 | BootDataVersion | Set to 0x210001 (BOOTDATA_VERSION_T210) |
| 0x4A4 | 0x4 | BlockSizeLog2 | Always 0xE |
| 0x4A8 | 0x4 | PageSizeLog2 | Always 0x9 |
| 0x4AC | 0x4 | PartitionSize | Always 0x1000000 |
| 0x4B0 | 0x4 | NumParamSets | Number of device parameter sets (always 0x1) |
| 0x4B4 | 0x4 | DevType | Device type (0x4 == Sdmmc) |
| 0x4B8 | 0x40 | DevParams | Device parameters |
| 0x4F8 | 0x4 | NumSdramSets | Number of SDRAM parameter sets (always set to 0, but parameters are used despite this) |
| 0x4FC | 0x838 | SdramParams0 | Default values filled in |
| 0xD34 | 0x838 | SdramParams1 | Default values filled in |
| 0x156C | 0x838 | SdramParams2 | Default values filled in |
| 0x1DA4 | 0x838 | SdramParams3 | Default values filled in |
| 0x25DC | 0x04 | BootLoadersUsed | Number of bootloaders installed (always 0x2, maximum is 0x4) |
| 0x25E0 | 0x10 | BootLoader0 | Configuration parameters for bootloader 0 (main)
0x25E0: StartBlock (0x40 for BootImagePackage, 0x100 for BootImagePackageSafe) 0x25E4: StartPage (0) 0x25E8: Version (variable) 0x25EC: Reserved |
| 0x25F0 | 0x10 | BootLoader1 | Configuration parameters for bootloader 1 (backup)
0x25F0: StartBlock (0x50 for BootImagePackage, 0x110 for BootImagePackageSafe) 0x25F4: StartPage (0) 0x25F8: Version (variable) 0x25FC: Reserved |
| 0x2600 | 0x10 | BootLoader2 | Reserved space for bootloader 2 (unused) |
| 0x2610 | 0x10 | BootLoader3 | Reserved space for bootloader 3 (unused) |
| 0x2620 | 0x4 | SecureDebugControlNoneEcid | Empty |
| 0x2624 | 0x4 | SecureDebugControlEcid | Empty |
| 0x2628 | 0x10 | Empty | |
| 0x2638 | 0x40 | Empty | |
| 0x2678 | 0x4 | SecProvisioningKeyNumSecure | Used for Factory Secure Provisioning (always 0) |
| 0x267C | 0x184 | Reserved | Always starts with 0x80000000 (NVBOOT padding pattern) |