Re: [PATCH v4 3/9] security: keys: trusted fix tpm2 authorizations

[Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>]

On Mon, 2020-01-06 at 23:45 +0200, Jarkko Sakkinen wrote:
> On Mon, 2019-12-30 at 09:37 -0800, James Bottomley wrote:
> > In TPM 1.2 an authorization was a 20 byte number.  The spec actually
> > recommended you to hash variable length passwords and use the sha1
> > hash as the authorization.  Because the spec doesn't require this
> > hashing, the current authorization for trusted keys is a 40 digit hex
> > number.  For TPM 2.0 the spec allows the passing in of variable length
> > passwords and passphrases directly, so we should allow that in trusted
> > keys for ease of use.  Update the 'blobauth' parameter to take this
> > into account, so we can now use plain text passwords for the keys.
> > 
> > so before
> > 
> > keyctl add trusted kmk "new 32 blobauthõ72d396fae9206628714fb2ce00f72e94f2258f"
> > 
> > after:
> > 
> > keyctl add trusted kmk "new 32 blobauth=hello keyhandle000001"
> > 
> > Note this is both and enhancement and a potential bug fix.  The TPM
> > 2.0 spec requires us to strip leading zeros, meaning empyty
> > authorization is a zero length HMAC whereas we're currently passing in
> > 20 bytes of zeros.  A lot of TPMs simply accept this as OK, but the
> > Microsoft TPM emulator rejects it with TPM_RC_BAD_AUTH, so this patch
> > makes the Microsoft TPM emulator work with trusted keys.
> 
> Even if for good reasons, you should be explicit when you make an API
> change that is not backwards compatible.

Also you have illformed abbrevation in your short summary. Should
be TPM2, not tpm2.

/Jarkko