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AM263P4: Questions Regarding Verification When Using OTFA

ATSUKI IMADA
Prodigy 80 points

Part Number: AM263P4
Other Parts Discussed in Thread: SYSCONFIG

environment
SDK : 11.0.0.19
SysConfig : 1.25.0
TI Arm Clang Compiler Tools : 4.0.3.LTS

1.Verification of the XIP Region by SBL    
I have a question regarding Secure Boot.
For an HS-SE device, is it possible to verify the X.509 certificate of the XIP image (*.mcelf_xip) during boot?
(For HS-SE devices, is the file extension actually .mcelf_xip.hs rather than .mcelf_xip? If so, please interpret the file names below accordingly.)

Reference:
https://software-dl.ti.com/mcu-plus-sdk/esd/AM263PX/latest/exports/docs/api_guide_am263px/BOOTFLOW_XIP.html
We are asking because the document states "Signing and encrypting application image to be executed from flash enables this. AM263PX is equipped with OTFA (On-The-Fly-Authentication and Decryption) hardware module to authenticate and decrypt an application running from flash.", and we would like to confirm whether verification is also performed during the boot process.

2.Verification of the XIP Region at Runtime
I have a question regarding OTFA.
When the application accesses the XIP region at runtime, is it correct to understand that verification is performed on a block-by-block basis, including the block containing the accessed address?
Also, is this verification performed using the X.509 certificate associated with the image?
If not, could you please explain what type of verification mechanism is used?
In addition, my understanding is that decryption is performed on AES blocks. Is this understanding correct?

3.Location of the Certificate for .mcelf_xip
We are considering a configuration in which the non-XIP regions are authenticated through Secure Boot, while the XIP region is protected using OTFA.
When a *.mcelf_xip image is signed, is the X.509 certificate appended to the beginning of the image file?
In addition, after the image is programmed to Flash, where is the X.509 certificate stored?
Could you please clarify whether the certificate is stored as part of the image in Flash, or in a separate location?

Requested response date: September 15, 2026

  • 0
    TI__Guru* 91121 points

    Hi,

    Please expect a response from the experts by 15 Sept, due to the holiday in India on 14th Sept.

    Thanks and Regards,

    Nikhil Dasan

  • 0 in reply to Nikhil Dasan
    TI__Genius 9655 points

    Hi Imada,

    For the XIP image, the verification is done during run time via the OTFA block. Unlike normal application were image authentication is done on boot, xip image does not support. The OTFA hardware only knows the authentication key programmed into its registers during boot. It has no concept of certificates or public keys.

    OTFA reads happen in 32 Byte blocks as mentioned in the TRM

    Thanks & Regards,

    Aswin