[tpm2] Re: inconsistent arguments

[tpm2] Re: inconsistent arguments

[Roberts, William C]

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> -----Original Message-----
> From: Alexander Lieb [mailto:alexander.lieb(a)online.de]
> Sent: Wednesday, January 8, 2020 11:28 AM
> To: Roberts, William C <william.c.roberts(a)intel.com>
> Cc: tpm2(a)lists.01.org
> Subject: Aw: [tpm2] Re: inconsistent arguments
> 
> Thanks for the fast reply.
> 
> So it is not possible at the moment to decrypt a message using an AK?

Correct. You would want to create a different key with attributes suited for
this.

> 
> Gesendet: Mittwoch, 08. Januar 2020 um 18:11 Uhr
> Von: "Roberts, William C" <william.c.roberts(a)intel.com>
> An: "Alexander Lieb" <alexander.lieb(a)online.de>, "tpm2(a)lists.01.org"
> <tpm2(a)lists.01.org>
> Betreff: [tpm2] Re: inconsistent arguments
> 
> 
> > -----Original Message-----
> > From: Alexander Lieb [mailto:alexander.lieb(a)online.de]
> > Sent: Wednesday, January 8, 2020 11:00 AM
> > To: tpm2(a)lists.01.org
> > Subject: [tpm2] inconsistent arguments
> >
> > Hi everyone,
> >
> > why does
> >
> > tpm2_createak -C ek.handle -c ak.ctx -u ak.pub -n ak.name -f pem
> >
> > openssl rsautl -encrypt -inkey ak.pub -pubin -in plaintext.txt -out
> > chiffre.enc
> >
> > tpm2_rsadecrypt -c ak.ctx -o plain.txt chiffre.enc
> >
> > result into
> >
> > ERROR:esys:src/tss2-esys/api/Esys_RSA_Encrypt.c:103:Esys_RSA_Encrypt()
> > Esys Finish ErrorCode (0x00000182)
> > ERROR: Esys_RSA_Encrypt(0x182) - tpm:handle(1):inconsistent attributes
> > ERROR: Unable to run tpm2_rsaencrypt
> 
> Looks like decrypt attribute is turned down:
> https://github.com/tpm2-software/tpm2-
> tools/blob/28221e5b0c9fc52029bdd96484fb85772601c4b0/tools/tpm2_createak.c
> #L142
> 
> I think it was chosen because an attestation key is typically used in a sign/verify
> pattern. Sign on TPM verify with public key on Attestation verifier side.
> 
> I'm not sure if there is a template specified for the attestation key in the spec, I
> can only find spec defined SRK and EK templates:
> - https://trustedcomputinggroup.org/wp-content/uploads/TCG-TPM-v2.0-
> Provisioning-Guidance-Published-v1r1.pdf
> 
> But that specific set of parameters for the AK template predates me, and I am
> not sure exactly why it was chosen.
> 
> >
> > ?
> >
> > (the same happens if I use tpm2_rsaencrypt)
> >
> > To give some context: I would like to do something like a challenge-response.
> >
> > There are two ways to do this:
> >
> > 1. Sending a nonce and let the tpm sign it using an ak (no idea how to do this) 2.
> > Send an ecrypted message and let the tpm decrypt it (this is what
> > shall happen
> > above)
> >
> > Are there any examples out there which I missed? Or can you help me in
> > any different way?
> >
> > Thanks a lot!
> >
> > Best regards
> > Alex
> >
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[tpm2] Re: inconsistent arguments

[Alexander Lieb]

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[tpm2] Re: inconsistent arguments

[Roberts, William C]

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> -----Original Message-----
> From: Alexander Lieb [mailto:alexander.lieb(a)online.de]
> Sent: Wednesday, January 8, 2020 11:00 AM
> To: tpm2(a)lists.01.org
> Subject: [tpm2] inconsistent arguments
> 
> Hi everyone,
> 
> why does
> 
>     tpm2_createak -C ek.handle -c ak.ctx -u ak.pub -n ak.name -f pem
> 
>     openssl rsautl -encrypt -inkey ak.pub -pubin -in plaintext.txt -out chiffre.enc
> 
>     tpm2_rsadecrypt -c ak.ctx -o plain.txt chiffre.enc
> 
> result into
> 
> ERROR:esys:src/tss2-esys/api/Esys_RSA_Encrypt.c:103:Esys_RSA_Encrypt() Esys
> Finish ErrorCode (0x00000182)
> ERROR: Esys_RSA_Encrypt(0x182) - tpm:handle(1):inconsistent attributes
> ERROR: Unable to run tpm2_rsaencrypt

Looks like decrypt attribute is turned down:
https://github.com/tpm2-software/tpm2-tools/blob/28221e5b0c9fc52029bdd96484fb85772601c4b0/tools/tpm2_createak.c#L142

I think it was chosen because an attestation key is typically used in a sign/verify pattern. Sign on TPM verify with public key on
Attestation verifier side.

I'm not sure if there is a template specified for the attestation key in the spec, I can only find spec defined
SRK and EK templates:
  - https://trustedcomputinggroup.org/wp-content/uploads/TCG-TPM-v2.0-Provisioning-Guidance-Published-v1r1.pdf

But that specific set of parameters for the AK template predates me, and I am not sure exactly why it was chosen.

> 
> ?
> 
> (the same happens if I use tpm2_rsaencrypt)
> 
> To give some context: I would like to do something like a challenge-response.
> 
> There are two ways to do this:
> 
> 1. Sending a nonce and let the tpm sign it using an ak (no idea how to do this) 2.
> Send an ecrypted message and let the tpm decrypt it (this is what shall happen
> above)
> 
> Are there any examples out there which I missed? Or can you help me in any
> different way?
> 
> Thanks a lot!
> 
> Best regards
> Alex
>