[tpm2] Re: Re-provision TPM

[Anthony Arrascue <AArrascue at neuroloop.de>]

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A way of re-provisioning (on a different OS image) that worked for me is the following:

tpm2_startup
#This clears the persistent storage
tpm2_clear
#To change profile from ECC to RSA
sed -i 's/"profile_name": "P_ECCP256SHA256"/"profile_name": "P_RSA2048SHA256"/g' /usr/local/etc/tpm2-tss/fapi-config.json
#Delete existing keystores
rm -rf ~/.local/share/tpm2-tss/user/keystore
rm -rf /usr/local/var/lib/tpm2-tss/system/keystore
#Before we provision we need to generate an EK
tpm2_createprimary -C e -g sha256 -G rsa -c endorsementprimary.ctx
tpm2_create -C endorsementprimary.ctx -g sha256 -G rsa -u rsak.pub -r rsak.priv
tpm2_load -C endorsementprimary.ctx -u rsak.pub -r rsak.priv -n rsak.name -c rsak.ctx
tpm2_evictcontrol -c rsak.ctx 0x81010001
tss2_provision

Without the tpm2_createprimary I would get an error when I use tss2_provision (something like “key cannot be signed”. I cannot remember the error message, but it contained the word EK).

Some questions that came to my mind:

  1.  Can all of this be done using only Fapi (no tpm2 commands)
  2.  Why is generating an EK required for provisioning? (which documentation describes this step)
  3.  Previous versions of the tpm2-tools had also a tpm2_takeownership. What happened with it and how to provision with owner’s authorization?

Thank you very much for your comments.
Best,
Anthony





From: Anthony Arrascue
Sent: Tuesday, 1 June 2021 19:18
To: 'tpm2(a)lists.01.org' <tpm2(a)lists.01.org>
Subject: Re-provision TPM

Hello,

I am learning about the TSS and TPM techonologies.
I have provisioned the TPM with the default settings, which means I am now using the ECC profile (P_ECCP256SHA256).
However, encryption was a requirement I needed to fulfill. I just didn't know that ECC encryption is currently not supported and now I realize RSA would be a better fit for me.
So here is my question:

  *   I see there is another profile in /usr/local/etc/tpm2-tss/fapi-profiles, namely P_RSA2048SHA256.json. Is there a way I can encrypt using the RSA profile instead of the ECC one? I tried to re-run tss2_provision, after setting it in fapi-config.json, but it seems this is not the way to proceed. I get the message that the TPM has been already provisioned. What is the correct way of "changing" profile? Is it even possible or do I need to reset the TPM?
Thank you for your help.
Anthony Arrascue


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