[tpm2] Re: Lifecycle of handles and contexts

[Roberts, William C <william.c.roberts at intel.com>]

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On Sat, 2022-07-16 at 14:20 +0000, Tim K wrote:
> Is there a good resource that describes the lifecycle of handles and
> contexts, in easy to understand terms?

Not great, but the TPM spec does have a section on it:
  - Section 15 of 
https://trustedcomputinggroup.org/wp-content/uploads/TPM-Rev-2.0-Part-1-Architecture-01.38.pdf


They key to know when you get a Handle the high byte determines the
type of handle, when you know the type you can know the lifecycle.

> 
> For example, if I create a primary key and then create a key and seal
> some data, I can keep unsealing the data without reloading the key.
> But if I reboot the computer, I have to create the primary key again
> and reload the key then I can unseal multiple times. So these keys
> get stored in the TPM until reboot it seems.

Correct, they are both transient objects with a high byte of 0x80.
 
> 
> Is there a way to flush them out of the TPM or even list what's
> stored? 

TPM2 Command TPM2_GetCap can show you what's loaded and
TPM2_FlushContext will flush them. Their are matching APIs and tools in
the tpm2-tss and tpm2-tools project. NOTE that when using a resource
manager like tpm2-abrmd or /dev/tpmrm0 that transient objects are
flushed when the application exits or closes the connection with the
resource manager.

> 
> Is there a way to list what's stored, what keys are loaded? 

For example with the tpm2-tools NOT USING A RESOURCE MANAGER:

# create
tpm2 createprimary

# list
tpm2 getcap --tcti=mssim handles-transient
- 0x80000000

# note 0x80 start, so transient
tpm2 flushcontext --tcti=mssim 0x80000000

tpm2 getcap --tcti=mssim handles-transient
# gone

> What about flushing them out without rebooting?

flushcontext

> 
> Thanks!
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