linux-kernel - Re: TPMs and random numbers

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Message-ID: <1378925224.26698.90.camel@localhost>
Date:	Wed, 11 Sep 2013 14:47:04 -0400
From:	David Safford <safford@...ibm.com>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	Leonidas Da Silva Barbosa <leosilva@...ux.vnet.ibm.com>,
	Ashley Lai <ashley@...leylai.com>,
	Rajiv Andrade <mail@...jiv.net>,
	Marcel Selhorst <tpmdd@...horst.net>,
	Sirrix AG <tpmdd@...rix.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Jeff Garzik <jgarzik@...ox.com>, "Ted Ts'o" <tytso@....edu>,
	Kent Yoder <key@...ux.vnet.ibm.com>,
	David Safford <safford@...son.ibm.com>,
	Mimi Zohar <zohar@...ibm.com>,
	"Johnston, DJ" <dj.johnston@...el.com>
Subject: Re: TPMs and random numbers

On Wed, 2013-09-11 at 10:49 -0700, Andy Lutomirski wrote:
> On Wed, Sep 11, 2013 at 10:22 AM, David Safford <safford@...ibm.com> wrote:
> >>On 09/09/2013 02:11 PM, H. Peter Anvin wrote:
> 
> A TPM that has an excellent internal entropy source and is FIPS 140-2
> compliant with no bugs whatsoever may still use Dual_EC_DRBG, which
> looks increasingly likely to be actively malicious.

I don't know of any that do so (it's more complex and slower than
the alternatives). 

> I'd be *much* happier if my system read a few hundred random bytes
> from the TPM at startup and fed those bytes into the kernel's entropy
> pool.  This should IMO happen at startup as early as possible.

I agree completely that the ideal case is a system with good entropy
sources, including a TPM, and all these mixed as early as possible.
But I also think that the existing (certified) TPMs are good enough 
for direct use.

dave


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