Subject: Re: [Teep] Keeping Secrets from the TAM

From: Brendan Moran <[email-masked]>
Date: Fri, 30 Jul 2021 00:29:31 +0000

The current text for section 9.8 of draft-ietf-teep-architecture-15 says:

One way to do this is for
   the Trusted Component Signer to run its own TAM so that it can
   distribute the decryption key via the TEEP protocol, and the key file
   can be a dependency in the manifest of the encrypted TA.  Thus, the
   TEEP Agent would look at the Trusted Component manifest, determine
   there is a dependency with a TAM URI of the Trusted Component
   Signer's TAM.  The Agent would then install the dependency, and then
   continue with the Trusted Component installation steps, including
   decrypting the TA binary with the relevant key.

While this is possible, it’s not the approach I would choose for TEEP. For TEEP, I would use either the HPKE or ECDH-ES + A(128/192/256)KW options from draft-tschofenig-suit-firmware-encryption. Then, the TC Signer provides a service that the TAM can query, where it will provide a COSE_Encrypt targeted to any specified device, subject to attestation and security posture assessment. This is much lighter-weight.

Best Regards,
Brendan
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