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

[Jarkko Sakkinen]

On Mon, Oct 14, 2019 at 12:29:57PM -0700, James Bottomley wrote:
> The job of the in-kernel rng is simply to produce a mixed entropy pool
> from which we can draw random numbers.  The idea is that quite a few
> attackers have identified the rng as being a weak point in the security
> architecture of the kernel, so if we mix entropy from all the sources
> we have, you have to compromise most of them to gain some predictive
> power over the rng sequence.

The documentation says that krng is suitable for key generation.
Should the documentation changed to state that it is unsuitable?

> The point is not how certified the TPM RNG is, the point is that it's a
> single source and if we rely on it solely for some applications, like
> trusted keys, then it gives the attackers a single known point to go
> after.  This may be impossible for script kiddies, but it won't be for
> nation states ... are you going to exclusively trust the random number
> you got from your chinese certified TPM?

I'd suggest approach where TPM RNG result is xored with krng result.

> Remember also that the attack doesn't have to be to the TPM only, it
> could be the pathway by which we get the random number, which involves
> components outside of the TPM certification.

Yeah, I do get this.

/Jarkko