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From: Pascal Van Leeuwen <pvanleeuwen@verimatrix.com>
To: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>,
	Ken Goldman <kgold@linux.ibm.com>
Cc: "Safford, David (GE Global Research, US)" <david.safford@ge.com>,
	Mimi Zohar <zohar@linux.ibm.com>,
	"linux-integrity@vger.kernel.org"
	<linux-integrity@vger.kernel.org>,
	"stable@vger.kernel.org" <stable@vger.kernel.org>,
	"open list:ASYMMETRIC KEYS" <keyrings@vger.kernel.org>,
	"open list:CRYPTO API" <linux-crypto@vger.kernel.org>,
	open list <linux-kernel@vger.kernel.org>
Subject: RE: [PATCH] KEYS: asym_tpm: Switch to get_random_bytes()
Date: Wed, 9 Oct 2019 08:02:52 +0000	[thread overview]
Message-ID: <MN2PR20MB29732A856A40131A671F949FCA950@MN2PR20MB2973.namprd20.prod.outlook.com> (raw)
In-Reply-To: <20191009073315.GA5884@linux.intel.com>

> -----Original Message-----
> From: linux-crypto-owner@vger.kernel.org <linux-crypto-owner@vger.kernel.org> On Behalf Of
> Jarkko Sakkinen
> Sent: Wednesday, October 9, 2019 9:33 AM
> To: Ken Goldman <kgold@linux.ibm.com>
> Cc: Safford, David (GE Global Research, US) <david.safford@ge.com>; Mimi Zohar
> <zohar@linux.ibm.com>; linux-integrity@vger.kernel.org; stable@vger.kernel.org; open
> list:ASYMMETRIC KEYS <keyrings@vger.kernel.org>; open list:CRYPTO API <linux-
> crypto@vger.kernel.org>; open list <linux-kernel@vger.kernel.org>
> Subject: Re: [PATCH] KEYS: asym_tpm: Switch to get_random_bytes()
> 
> 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.
> 
I do understand that, and combining multiple entropy sources, if
you have them available to get _more_ entropy is a good idea, at 
least in theory. But ...

How do I know the mixing of entropy happens properly? Especially
if I'm not capable of judging this by myself. 
And how do I know the SW entropy pool and/or code cannot be influenced
_somehow_? (either directly or indirectly by influencing one of the
contributors). More code and/or HW involved means more attack vectors
and complication of the review process.

The point is, if you want to certify such an application, you would
have to have _all_ contributors _plus_ the kernel rng code certified.
And you would have to have it _recertified_ every time a _single_
component - including the kernel code itself! - changes.

> Even with weaker entropy than TPM RNG it is still a better choice for
> *non-TPM* keys because of better trustworthiness.
>
"Even with weaker entropy"? Now that's just silly. If you _know_ and
_trust_ the TPM to have _better_ entropy, then obviously that is the
better choice. I guess the key word being the trust you don't have.

> 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.
>
For non-TPM keys, possibly. Assuming the kernel RNG indeed adds 
(or at least does not weaken) entropy. And assuming I _can_ trust
the kernel RNG implementation. Question is: why would I trust that
more than the TPM implementation? Sure, I could look at the code,
but would I truly and fully understand it? (so maybe _I_ would,
but would Joe Random User?)

> Please remember that a trusted key is not a TPM key. The reality
> distortion field is strong here it seems.
> 
Agree. But you should not mess with the possibility to generate
keys based on _just_ the TPM RNG _where that is required_ (and
perhaps _only_ where that is required, if possible)

> /Jarkko

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


  parent reply	other threads:[~2019-10-09  8:03 UTC|newest]

Thread overview: 58+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-09-26 17:16 Jarkko Sakkinen
2019-09-28 18:05 ` Jerry Snitselaar
2019-10-01 20:54   ` Jarkko Sakkinen
2019-10-02 14:00 ` Mimi Zohar
2019-10-03 11:41   ` Jarkko Sakkinen
2019-10-03 11:43     ` Jarkko Sakkinen
2019-10-03 13:02     ` Mimi Zohar
2019-10-03 17:58       ` Jarkko Sakkinen
2019-10-03 18:53         ` Mimi Zohar
2019-10-03 21:51           ` Jarkko Sakkinen
2019-10-03 21:57             ` Jarkko Sakkinen
2019-10-03 22:08               ` Mimi Zohar
2019-10-03 23:59                 ` James Bottomley
2019-10-04 18:22                   ` Jarkko Sakkinen
2019-10-04 18:24                     ` James Bottomley
2019-10-04 18:33                       ` Jerry Snitselaar
2019-10-04 18:42                         ` James Bottomley
2019-10-04 20:07                           ` Jerry Snitselaar
2019-10-04 20:11                             ` Jerry Snitselaar
2019-10-04 22:11                               ` James Bottomley
2019-10-06  0:38                                 ` Mimi Zohar
2019-10-06 23:52                                   ` Jarkko Sakkinen
2019-10-07 18:08                                     ` Mimi Zohar
2019-10-04 18:20                 ` Jarkko Sakkinen
2019-10-03 22:10               ` Jarkko Sakkinen
2019-10-04 13:26           ` Safford, David (GE Global Research, US)
2019-10-04 18:27             ` Jarkko Sakkinen
2019-10-04 18:30               ` Jarkko Sakkinen
2019-10-04 19:56               ` Safford, David (GE Global Research, US)
2019-10-07  0:05                 ` Jarkko Sakkinen
2019-10-07 22:13                   ` Ken Goldman
2019-10-08 23:49                     ` Jarkko Sakkinen
2019-10-08 23:53                       ` Jarkko Sakkinen
2019-10-09  7:10                         ` Pascal Van Leeuwen
2019-10-09  7:33                         ` Jarkko Sakkinen
2019-10-09  7:41                           ` Jarkko Sakkinen
2019-10-09  8:09                             ` Pascal Van Leeuwen
2019-10-14 19:11                               ` Jarkko Sakkinen
2019-10-09  8:02                           ` Pascal Van Leeuwen [this message]
2019-10-09 12:11                         ` Safford, David (GE Global Research, US)
2019-10-14 19:00                           ` Jarkko Sakkinen
2019-10-14 19:29                             ` Jarkko Sakkinen
2019-10-14 19:29                             ` James Bottomley
2019-10-16 11:00                               ` Jarkko Sakkinen
2019-10-16 12:34                                 ` James Bottomley
2019-10-16 16:25                                   ` Jarkko Sakkinen
2019-10-16 19:10                                     ` James Bottomley
2019-10-17 12:52                                       ` Sumit Garg
2019-10-17 12:58                                         ` James Bottomley
2019-10-17 18:04                                       ` Jarkko Sakkinen
2019-10-21 11:39                                         ` Jarkko Sakkinen
2019-10-29  8:42                                           ` Jarkko Sakkinen
2019-10-29 14:58                                             ` James Bottomley
2019-10-31 21:03                                               ` Jarkko Sakkinen
2019-10-18  7:32                                   ` Janne Karhunen
2019-10-03 18:02       ` Jarkko Sakkinen
2019-10-03 18:15         ` Jarkko Sakkinen
2019-10-07 10:33     ` Janne Karhunen

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