1 1. Setup U-Boot Image for Encrypted Boot
2 ----------------------------------------
3 An authenticated U-Boot image is used as starting point for
4 Encrypted Boot. The image is encrypted by i.MX Code Signing
5 Tool (CST). The CST replaces only the image data of
6 u-boot-dtb.imx with the encrypted data. The Initial Vector Table,
7 DCD, and Boot data, remains in plaintext.
9 The image data is encrypted with a Encryption Key (DEK).
10 Therefore, this key is needed to decrypt the data during the
11 booting process. The DEK is protected by wrapping it in a Blob,
12 which needs to be appended to the U-Boot image and specified in
15 The DEK blob is generated by an authenticated U-Boot image with
16 the dek_blob cmd enabled. The image used for DEK blob generation
17 needs to have the following configurations enabled in Kconfig:
22 Note: The encrypted boot feature is only supported by HABv4 or
25 The dek_blob command then can be used to generate the DEK blob of
26 a DEK previously loaded in memory. The command is used as follows:
28 dek_blob <DEK address> <Output Address> <Key Size in Bits>
29 example: dek_blob 0x10800000 0x10801000 192
31 The resulting DEK blob then is used to construct the encrypted
32 U-Boot image. Note that the blob needs to be transferred back
33 to the host.Then the following commands are used to construct
36 cat u-boot-dtb.imx csf-u-boot.bin > u-boot-signed.imx
37 objcopy -I binary -O binary --pad-to <blob_dst> --gap-fill=0x00 \
38 u-boot-signed.imx u-boot-signed-pad.bin
39 cat u-boot-signed-pad.imx DEK_blob.bin > u-boot-encrypted.imx
41 NOTE: u-boot-signed.bin needs to be padded to the value
42 equivalent to the address in which the DEK blob is specified