Depends on the PLL design - which we don't know. But yes, generally they are notoriously sensitive to thermal effects.
I think my point is valid though - even if it is a PRNG, provided it's a good one (and distribution will tell you that) if an attacker can't tell exactly when you are sampling the PRNG effectively it's a usable entropy source. There are use cases where it may not be a good source - as in my previous comments, a smart card for example, where the owner has pysical access and *can* dunk it into a thermos full of liquid nitrogen ;) but in most of the OpenSSL use cases it's reasonable to exclude those scenarios. The same is true of events we consider to be really random - i.e. radioactive material, thermal shot noise - the real situation may simply be that we don't yet know enough at present to be able to predict when an indivdual nucleus will decay - that doesn't mean that'll always be true or that someone with physical access to the hardware can't fake the 'random' events anyway. Peter From: Andy Polyakov <[email protected]> To: [email protected] Date: 18/01/2012 01:53 Subject: Re: OS-independent entropy source? Sent by: [email protected] > In praxis the feedback loop will exhibit both deterministic > (e.g. quantization) and random (thermal) noise. For example > if the common input clock changes, feedback loops in both > PLLs go through their transfer functions until they stabilize > on the new frequency. The resulting jitter will probably > appear quite random, but is not. Maybe relevant question is not how [in]predictable is PLL's reaction on input frequency variation, but that there is one. I mean even if PLL reaction is predictable, *when* [thermal] variation and consequent reaction occurs is not, right? ______________________________________________________________________ OpenSSL Project http://www.openssl.org Development Mailing List [email protected] Automated List Manager [email protected] ______________________________________________________________________ OpenSSL Project http://www.openssl.org Development Mailing List [email protected] Automated List Manager [email protected]
