[tpm2] Re: Fapi_Decrypt using auth value

[tpm2] Re: Fapi_Decrypt using auth value

[Fuchs, Andreas]

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Hi Anthony,

in FAPI the authValues are always asked for using the callback registered in Fapi_SetAuthCB.
The simplest to do this (as I did a few times) in a programs is

TSS2_RC myAuthCB(..., const char **auth, void* userdata) {
    *auth = (char *) userdata;
    return TSS2_RC_SUCCESS;
}

static const char *myauth = "password";
Fapi_SetAuthCB(ctx, myAuthCB, myauth);
Fapi_Decrypt(ctx, ...);
Fapi_setAuthCB(ctx, NULL, NULL);

Hope this helps you.

Cheers,
Andreas

________________________________________
Von: Anthony Arrascue <AArrascue(a)neuroloop.de>
Gesendet: Mittwoch, 30. Juni 2021 12:37
An: tpm2(a)lists.01.org
Betreff: [tpm2] Fapi_Decrypt using auth value

Hello,

I am learning about encryption / decryption using Fapi.
For that purpose, I create a key using tss2_createkey and use tss2_encrypt / tss2_decrypt (and their Fapi equivalents).

tss2_ createkey has the argument -a, --authValue to set up a decryption password.
With tss2_encrypt I generate the cipher text.

The problem is with the decryption process. When I decrypt with tss2_decrypt I got asked for that authValue. If it is given correctly it decrypts the cipher text. However, Fapi_Decrypt will fail throwing an authorization error.

I was wondering how to programmatically enter the authValue? Fapi_Decrypt has no arguments to pass it. Maybe through the FAPI_CONTEXT?

Using TPM2-TSS v. 2.4.x
TPM2-TOOLS v. 4.X

Thank you for any possible help.
Best,


Anthony Arrascue
--------------------------------------
neuroloop GmbH
Breisacher Str. 86, 79110 Freiburg, Germany
aarrascue(a)neuroloop.de<mailto:aarrascue(a)neuroloop.de>
neuroloop.de

[tpm2] Re: Fapi_Decrypt using auth value

[Anthony Arrascue]

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Hi Andreas,

Thank you! I will try that.

Best,

Anthony

> -----Original Message-----
> From: Fuchs, Andreas <andreas.fuchs(a)sit.fraunhofer.de>
> Sent: Wednesday, 30 June 2021 13:25
> To: Anthony Arrascue <AArrascue(a)neuroloop.de>; tpm2(a)lists.01.org
> Subject: AW: Fapi_Decrypt using auth value
> 
> Hi Anthony,
> 
> in FAPI the authValues are always asked for using the callback registered in
> Fapi_SetAuthCB.
> The simplest to do this (as I did a few times) in a programs is
> 
> TSS2_RC myAuthCB(..., const char **auth, void* userdata) {
>     *auth = (char *) userdata;
>     return TSS2_RC_SUCCESS;
> }
> 
> static const char *myauth = "password";
> Fapi_SetAuthCB(ctx, myAuthCB, myauth);
> Fapi_Decrypt(ctx, ...);
> Fapi_setAuthCB(ctx, NULL, NULL);
> 
> Hope this helps you.
> 
> Cheers,
> Andreas
> 
> ________________________________________
> Von: Anthony Arrascue <AArrascue(a)neuroloop.de>
> Gesendet: Mittwoch, 30. Juni 2021 12:37
> An: tpm2(a)lists.01.org
> Betreff: [tpm2] Fapi_Decrypt using auth value
> 
> Hello,
> 
> I am learning about encryption / decryption using Fapi.
> For that purpose, I create a key using tss2_createkey and use tss2_encrypt /
> tss2_decrypt (and their Fapi equivalents).
> 
> tss2_ createkey has the argument -a, --authValue to set up a decryption
> password.
> With tss2_encrypt I generate the cipher text.
> 
> The problem is with the decryption process. When I decrypt with
> tss2_decrypt I got asked for that authValue. If it is given correctly it decrypts
> the cipher text. However, Fapi_Decrypt will fail throwing an authorization
> error.
> 
> I was wondering how to programmatically enter the authValue?
> Fapi_Decrypt has no arguments to pass it. Maybe through the
> FAPI_CONTEXT?
> 
> Using TPM2-TSS v. 2.4.x
> TPM2-TOOLS v. 4.X
> 
> Thank you for any possible help.
> Best,
> 
> 
> Anthony Arrascue
> --------------------------------------
> neuroloop GmbH
> Breisacher Str. 86, 79110 Freiburg, Germany
> aarrascue(a)neuroloop.de<mailto:aarrascue(a)neuroloop.de>
> neuroloop.de
>