Messages in this thread | | | Date | Thu, 12 Sep 2013 18:13:40 -0400 | From | Jörn Engel <> | Subject | Re: TPMs and random numbers |
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On Thu, 12 September 2013 19:39:47 -0400, Jeff Garzik wrote: > On Thu, Sep 12, 2013 at 5:57 PM, Jörn Engel <joern@logfs.org> wrote: > > On Wed, 11 September 2013 14:47:04 -0400, David Safford wrote: > >> But I also think that the existing (certified) TPMs are good enough > >> for direct use. > > > That is equivalent to trusting the TPM chip not to be malicious. It > > Indeed. While it need not be rngd or userland at all, it seems > reasonable to require any hardware RNG to have its data pushed through > AES mix steps (as kernel random does now IIUC).
*shrug*
The hardware RNG is either providing good entropy or entirely predictable data - without us being able to tell the difference. So I am torn between two extremes. Either we admit it to the entropy pool and mix it will all other sources - hoping that it actually is unpredictable to The Bad Guys(tm). Or we disregard all of it.
If we disregard all of it, that forces us to collect good entropy from other sources. Having what looks like good entropy but may not be will a) make us complacent and b) make it hard to notice when our random numbers are compromised. It is the same strategy as burning down the bridge, forcing your army to win or die. It also shares the same drawbacks.
Jörn
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