Hash of Image during confirm the firmware

Hi,

I'm looking to implement the smp protocol in my central device based on nrf5 sdk, in order to update my new peripheral device based on ncs v2.6.1.

My questions are : how to generate the hash image sended when you want to confirm the image previously sended.

Do you have any documentation or explication about it ? 

I saw that is a sha256 encryption, but i do not know which data i need to perform this encryption.

Thanks in advance.

Regards,

Julien

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