Dear TF-M Community,
I have a question regarding rollback protection in Internal Trusted Storage.
Scenario: Recently we are seeing an increasing number of products which will come to market without internal Flash; together with this, there is also the requirement to store permanent keys using PSA key management APIs as psa_import_key, which will then in turn use Internal Trusted Storage as place where keys will be written. Considering these requirements there is a necessity to implement the Internal Trusted Storage in external Flash, which brings with it security challenges: the keys stored in external Flash would require confidentiality but also rollback protection. The encryption of ITS encryption was recently enabled as you can see in the following Pull request https://review.trustedfirmware.org/c/TF-M/trusted-firmware-m/+/15096, but rollback protection is not yet implemented.
Proposal: Our proposal would be to: - Add ITS rollback protection as optional feature, since it is not desired feature for product where the ITS storage is internal - Add rollback protection mechanism to Internal Trusted Storage functions relying on the NV counters APIs called from the platform layer, similar as is already done for Protected Storage
Also, we are open to discuss any other proposal which would help us to fulfill the above requests (ITS in external Flash with still providing confidentiality and rollback protection).
Thanks in advance for the answer and further guidance on the topic.
KR, Bojan Simoneta
Bojan Simoneta (He / Him / His) Principal Embedded SW Engineer Phone: +433124 299160 Email: bojan.simoneta@nxp.commailto:bojan.simoneta@nxp.com
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