There is any secure storage in NRF52840

[alireza sadeghpour]

Hi, 

i am developing an based on NRF52840 and i need to save some credentials and keys in a secure storage and keep them in power cycles, there is any secure storage in NRF52840 that i can use?

i readed something about Trustzone and Cryptocell, Do they provide a secure storage?

[haakonsh]

You can use the ACL — Access control lists to disable W/R operations on specific parts of the flash. 

You can for instance store a key in flash, load it into Cryptocell'ss secure RAM, then turn of read/write access to the part of flash that the key is stored in. At this point the CPU cannot access your key, debugger read access will be Read-As-Zero (RAZ), while debugger write access will be Write-Ignored (WI).

The ACL will release on a reset, it is therefore paramount that the flash is locked down with ACL immediately after the CPU is ready for execution, usually in a secure bootloader.