Re: FIT image verification not working on imx8mm

[Vyacheslav Yurkov <uvv.mail@gmail.com>]

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Hi Michael,
I believe the message is correct:

 > Verifying Hash Integrity ... sha256+ OK

The "+" sign means the signature verification succeeded. The "-" would 
mean otherwise.

I've just tried again to boot a fit image built without 
UBOOT_SIGN_ENABLE and got:

 > No 'signature' subnode found for '<NULL>' hash node in 'conf-my-dtb' 
config node

Do you use the u-boot as SPL by any chance?

Slava

On 21.02.2026 11:39, Michael Opdenacker wrote:
>
> Greetings,
>
> For a secure boot project on Toradex Verdin with imx8mm, I'm trying to 
> enable FIT image signature verification in U-Boot.
>
> Slava's "Generation of FIT images" presentation at the recent OE 
> workshop has been very useful:
> https://pretalx.com/media/openembedded-workshop-2026-2025/submissions/R8KJQZ/resources/_LJtpFTR.pdf
>
> I generated a temporary local RSA 2048 key, and I'm using it to sign a 
> FIT image.
>
> I also set the UBOOT_SIGN_KEYDIR, UBOOT_SIGN_KEYNAME and 
> UBOOT_SIGN_ENABLE variables to add the public key to U-Boot's DTB.
>
> The signature indeed appears in the generated u-boot.dtb file, in a 
> "/signature" node:
>
>     signature {
>
>         key-imx8mmsb {
>             required = "conf";
>             algo = "sha256,rsa2048";
>             rsa,r-squared = <0x56bb2a2b 0xc6b322cc 0x2f828666 
> 0x75c8bc46 0xd13093af 0xc2244c35 0xb6420649 0x478d7ed3 0xeb7a0399 
> 0x3b1d49a9 0xc106169d 0x7328dbb4 0x2140c49b 0x111732a1 0xb3286fed 
> 0x53937163 0x8c28f85c 0xe272b1ee 0x5e009a53 0x13883205 0xcda0fbc7 
> 0xd7ed4e75 0x9ed065c1 0xb6ca1e69 0xf2c9dce2 0xcf8ebf7b 0x59a72b94 
> 0x501d2751 0x437e3355 0xcba6b07a 0x9b13feea 0x1032d715 0xab3cdd83 
> 0x319b6bb0 0xfc31ff93 0xb7fabbb6 0x79d5d0fa 0x9c0f76e0 0x3528c22e 
> 0xbbec6d6c 0x7981362f 0x528848a9 0xb57aa235 0x462ed577 0x4ccc8b9d 
> 0xeb4ce969 0x5fb085b3 0x3fced511 0xfd98edfe 0xf3a4ca51 0x1bb74370 
> 0x3a11c748 0xbbd5be95 0x946f8b3f 0x3d8c98b6 0x3b0e00a8 0xeca87fc6 
> 0x7331981e 0xaaee80df 0x476816f2 0x509aaab1 0xa5f50e1a 0x474d0de8 
> 0xc551ac97>;
>             rsa,modulus = <0xb3ade247 0x4b8d0aef 0x4581e5e9 0x6084f135 
> 0x778847c7 0xaf23976f 0x81b6eb84 0xa2406db4 0x2b89e624 0x81f913c9 
> 0xd6ebef10 0x3e30adee 0xbca06cbe 0x5693b23b 0xc6b211f1 0xfea7a90d 
> 0x2767ca7c 0xaa8b2ddb 0xcf8a63ea 0x66fe8c59 0x43b34a2f 0x720009d8 
> 0xa2a61281 0x2f7fe049 0xfc3d10e5 0x1b52409 0xdeb52a16 0xa4e5fa78 
> 0x7116d181 0xc0c2f39e 0x24a626b4 0x7e59438b 0x6680b1f4 0xc4b1184c 
> 0x8bb65f34 0x92038fd7 0x3901c347 0xc2095158 0x3159031a 0xaa4bb76c 
> 0xc53f2009 0x9f4941f8 0x736ca84a 0xd83bd011 0x3685d02c 0x6f4cb5e7 
> 0xd07e8566 0x173819f 0x8f41366d 0x8b0f82fd 0x54c01fc0 0xc216cbd5 
> 0x2fc4a666 0x426ff669 0x880428ca 0x7c7615c 0xcdc97895 0x8c936a3c 
> 0xd6d7e82e 0x5bf63d9d 0x9fcd83a2 0xb131015f 0xc530c031 0x8446f707>;
>             rsa,exponent = <0x00 0x10001>;
>             rsa,n0-inverse = <0x93653949>;
>             rsa,num-bits = <0x800>;
>             key-name-hint = "imx8mmsb";
>         };
>     };
>
> I also compiled U-Boot with
> |CONFIG_FIT_SIGNATURE=y
> |
> However, when U-Boot loads the FIT image, it only checks the integrity 
> of the sha256 hash of the FIT image parts:
>    Verifying Hash Integrity ... sha256+ OK
>
> No signature checking happens. I can also load an unsigned FIT image 
> which is accepted too. Indeed, when I open the generated "imx-boot" 
> file (or "flash.bin", linking to the same file) that is used to boot 
> the board, I can see a DTB for my board, but it doesn't contain any 
> "signature" node, unlike in "u-boot.dtb".
>
> What could I be missing? My layer, along with a kas file to generate 
> the image, is available on 
> https://gitlab.com/rootcommit/meta-imx8mm-secureboot. I'm using the 
> Toradex Easy Installer (Tezi) to flash the image on eMMC. My layer is 
> relies on the "master" branches of the required layers, but I have the 
> same problem on Scarthgap too.
>
> Any suggestions are appreciated.
> Thanks in advance
> Michael.
>
> -- 
> Root Commit
> Embedded Linux Training and Consulting
> https://rootcommit.com

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