RE: [PATCH] KEYS: asym_tpm: Switch to get_random_bytes()

[Pascal Van Leeuwen]

> -----Original Message-----
> From: linux-crypto-owner@xxxxxxxxxxxxxxx <linux-crypto-owner@xxxxxxxxxxxxxxx> On Behalf Of
> Jarkko Sakkinen
> Sent: Wednesday, October 9, 2019 9:42 AM
> To: Ken Goldman <kgold@xxxxxxxxxxxxx>
> Cc: Safford, David (GE Global Research, US) <david.safford@xxxxxx>; Mimi Zohar
> <zohar@xxxxxxxxxxxxx>; linux-integrity@xxxxxxxxxxxxxxx; stable@xxxxxxxxxxxxxxx; open
> list:ASYMMETRIC KEYS <keyrings@xxxxxxxxxxxxxxx>; open list:CRYPTO API <linux-
> crypto@xxxxxxxxxxxxxxx>; open list <linux-kernel@xxxxxxxxxxxxxxx>
> Subject: Re: [PATCH] KEYS: asym_tpm: Switch to get_random_bytes()
> 
> On Wed, Oct 09, 2019 at 10:33:15AM +0300, Jarkko Sakkinen wrote:
> > On Wed, Oct 09, 2019 at 02:53:39AM +0300, Jarkko Sakkinen wrote:
> > > On Wed, Oct 09, 2019 at 02:49:35AM +0300, Jarkko Sakkinen wrote:
> > > > On Mon, Oct 07, 2019 at 06:13:01PM -0400, Ken Goldman wrote:
> > > > > The TPM library specification states that the TPM must comply with NIST
> > > > > SP800-90 A.
> > > > >
> > > > > https://trustedcomputinggroup.org/membership/certification/tpm-certified-products/
> > > > >
> > > > > shows that the TPMs get third party certification, Common Criteria EAL 4+.
> > > > >
> > > > > While it's theoretically possible that an attacker could compromise
> > > > > both the TPM vendors and the evaluation agencies, we do have EAL 4+
> > > > > assurance against both 1 and 2.
> > > >
> > > > Certifications do not equal to trust.
> > >
> > > And for trusted keys the least trust solution is to do generation
> > > with the kernel assets and sealing with TPM. With TEE the least
> > > trust solution is equivalent.
> > >
> > > Are you proposing that the kernel random number generation should
> > > be removed? That would be my conclusion of this discussion if I
> > > would agree any of this (I don't).
> >
> > The whole point of rng in kernel has been to use multiple entropy
> > sources in order to disclose the trust issue.
> >
> > Even with weaker entropy than TPM RNG it is still a better choice for
> > *non-TPM* keys because of better trustworthiness. Using only TPM RNG is
> > a design flaw that has existed probably because when trusted keys were
> > introduced TPM was more niche than it is today.
> >
> > Please remember that a trusted key is not a TPM key. The reality
> > distortion field is strong here it seems.
> 
> And why not use RDRAND on x86 instead of TPM RNG here? It is also FIPS
> compliant and has less latency than TPM RNG. :-) If we go with this
> route, lets pick the HRNG that performs best.
> 
There's certification and certification. Not all certificates are
created equally. But if it matches your specific requirements, why not.
There's a _lot_ of HW out there that's not x86 though ...

And: is RDRAND certified for _all_ x86 processors? Or just Intel?
Or perhaps even only _specific (server) models_ of CPU's?
I also know for a fact that some older AMD processors had a broken
RDRAND implementation ...

So the choice really should be up to the application or user.

Regards,
Pascal van Leeuwen
Silicon IP Architect, Multi-Protocol Engines @ Verimatrix
www.insidesecure.com