PSA Initial attestation token signature verification

[dilip agrawal]

Hi 

We have received  Initial Attestation report from device using  psa_initial_attest_get_token  and we want to verify signature.

Today we don't know how signature is calculated inside psa_initial_attest_get_token  api, signing key that we set is of type SAH256 ECDSA ,

We have respective public  key and want to verify it .

this is the complete EAT token report 

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

I used cobr to format and we found below 

18([h'A10126', {}, h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h'A09B986B6B300280FD930916A6F42B122442159EC25A37B7AAAF0C559400C79F933279C80CAC735F9A07B8739DEC1A354D4953AAB46D6C5125F69A59EA8A6351'])

and here is the signature , we want to know how this signature is calculated, because we want to verify this signature out side of device. So if you have any exampls or links where signture varication is done it will be useful.

A09B986B6B300280FD930916A6F42B122442159EC25A37B7AAAF0C559400C79F933279C80CAC735F9A07B8739DEC1A354D4953AAB46D6C5125F69A59EA8A6351

Regards

Dilip

[Hieu]

Hi Dilip,

If I understand correctly, the reason you want to know how the signature is calculated is to perform a validation, right?

I will investigate this and get back to you soon.

Regards,

Hieu

[dilip agrawal]

yes Hieu

[Hieu]

Hi Dilip,

There is a tool for validating the Initial Attestation Token, provided by the Trusted Firmware org.

You can find its source code it here: https://git.trustedfirmware.org/TF-M/tf-m-tools.git/tree/iat-verifier?h=release%2F1.8.x.

From the source code, you will also be able to investigate the compilation and decompilation of a token.

Hieu