Difference between revisions of "BCT"

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|  0x04
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|  DevType
|  DevType
|  Device type. Set to 0x04 (dev_type_sdmmc).
|  Device type. Set to 0x04 (Sdmmc).
|  0x0548
|  0x0548

Revision as of 17:31, 29 July 2019

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.

By design, the BCT's data is only signed after offset 0x0510. 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.

During boot, the boot ROM parses the appropriate BCT from eMMC storage and stores a copy of it in IRAM at address 0x40000000.


Below is the BCT structure used by the Switch, which is a minimal variation of the Tegra 210 BCT format.

Offset Size Field Description
0x0000 0x210 BadBlockTable Table containing information on bad blocks
0x0000: EntriesUsed (0x200)
0x0004: VirtualBlockSizeLog2 (0x0F)
0x0005: BlockSizeLog2 (0x0E)
0x0006: BadBlocks
0x0206: Reserved
0x0210 0x100 Key BCT RSA public key's modulus
0x0310 0x110 Signature BCT object signature
0x0310: CryptoHash (empty)
0x0320: RsaPssSig
0x0420 0x04 SecProvisioningKeyNumInsecure Used for Factory Secure Provisioning. Always 0.
0x0424 0x20 SecProvisioningKey Used for Factory Secure Provisioning. Always empty.
0x0444 0xC4 CustomerData Data block available for the customer. Used in key generation.
0x0444: Reserved (0x0C bytes)
0x0450: Keyblob (0xB0 bytes)
0x0500: Reserved (0x08 bytes)
0x0508 0x04 OdmData Legacy field. Unused.
0x050C 0x04 Reserved Legacy field. Unused.
0x0510 0x10 RandomAesBlock Always empty.
0x0520 0x10 UniqueChipId Always empty.
0x0530 0x04 BootDataVersion Set to 0x00210001 (BOOTDATA_VERSION_T210).
0x0534 0x04 BlockSizeLog2 Always 0x0E.
0x0538 0x04 PageSizeLog2 Always 0x09.
0x053C 0x04 PartitionSize Always 0x01000000.
0x0540 0x04 NumParamSets Number of device parameter sets. Always 0x01.
0x0544 0x04 DevType Device type. Set to 0x04 (Sdmmc).
0x0548 0x40 DevParams Device parameters
 0x0548: ClockDivider (0x09 == 24MHz)
 0x054C: DataWidth (0x02 == 8Bit)
0x0588 0x04 NumSdramSets Number of SDRAM parameter sets. Always set to 0, but parameters are used despite this.
0x058C 0x768 SdramParams0 Default values filled in.
0x0CF4 0x768 SdramParams1 Default values filled in.
0x145C 0x768 SdramParams2 Default values filled in.
0x1BC4 0x768 SdramParams3 Default values filled in.
0x232C 0x04 BootLoadersUsed Number of bootloaders installed. Always 0x02 (maximum is 0x04).
0x2330 0x12C BootLoader0 Configuration parameters for bootloader 0 (normal).
0x2330: Version (variable)
0x2334: StartBlock (0x00000040)
0x2338: StartPage (0x00000000)
0x233C: Length (variable)
0x2340: LoadAddress (0x40010000)
0x2344: EntryPoint (0x40010020 for 1.0.0-3.0.2, 0x40010040 for 4.0.0+)
0x2348: Attribute (0x00000000)
0x234C: CryptoHash (empty)
0x235C: RsaPssSig
0x245C 0x12C BootLoader1 Configuration parameters for bootloader 1 (safe mode).
0x245C: Version (variable)
0x2460: StartBlock (0x00000050)
0x2464: StartPage (0x00000000)
0x2468: Length (variable)
0x246C: LoadAddress (0x40010000)
0x2470: EntryPoint (0x40010020 for 1.0.0-3.0.2, 0x40010040 for 4.0.0+)
0x2474: Attribute (0x00000000)
0x2478: CryptoHash (empty)
0x2488: RsaPssSig
0x2588 0x12C BootLoader2 Reserved space for bootloader 2 (unused).
0x26B4 0x12C BootLoader3 Reserved space for bootloader 3 (unused).
0x27E0 0x01 EnableFailBack Always 0.
0x27E1 0x04 SecureJtagControl Always 0.
0x27E5 0x04 SecProvisioningKeyNumSecure Used for Factory Secure Provisioning. Always 0.
0x27E9 0x12 Reserved Always starts with 0x80000000 (NVBOOT padding pattern).
0x27FB 0x05 Padding Empty. Not part of BCT data.


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


The version field controls which keyblob is used, where 0x01 is the first one. See Cryptosystem for the keyblobs used by each system-version.