Date: Mon, 20 Aug 2012 23:05:39 +0100 From: Ben Laurie <ben@links.org> To: Steve Kargl <sgk@troutmask.apl.washington.edu> Cc: freebsd-arch@freebsd.org Subject: Re: /dev/random Message-ID: <CAG5KPzwBzWvDFDZqzT4masbknKfVe-rvdTd1h6ZxEoG90Rcxqg@mail.gmail.com> In-Reply-To: <20120820220243.GA96700@troutmask.apl.washington.edu> References: <CAG5KPzz4GQ2C_ky_qrDroQ4srGL4daW0OO-F3eOvvL-9AO6zoQ@mail.gmail.com> <20120820220243.GA96700@troutmask.apl.washington.edu>
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On Mon, Aug 20, 2012 at 11:02 PM, Steve Kargl <sgk@troutmask.apl.washington.edu> wrote: > On Mon, Aug 20, 2012 at 07:49:16PM +0100, Ben Laurie wrote: >> Apparently /dev/random uses h/w PRNGs if available, discarding all >> other sources of randomness. >> >> This seems like a mistake to me - we should fix it. >> >> Also, it seems that entropy is available in detailed interrupt timing >> (see http://www.issihosts.com/haveged/) which might be useful on >> entropy-starved systems - I suspect we are not exploiting this source, >> and in light of recent developments, we probably should be, >> >> Comments? > > Well, it's hard to comment when you failed to explain > *why* you think it is a mistake. Sorry - because I do not think it is wise to trust the h/w prng so much we discard other entropy. > In addition, I'm having > a hard time parsing your 1st sentence, which appears to > be related to this sentence: > > The device will probe for certain hardware entropy sources, > and use these in preference to the fallback, which is a > generator implemented in software. > > from 'man 4 random'. Your 'all other sources of randomness' > would then need to be amended to 'all other sources of entropy'. > But, then 'all other sources' does not make sense, because only > the 'generator implemented in software' is discarded. That is everything except the hardware, right? So ... all other sources. > It is also unclear why a linux-only project for gathering entropy > is relevant here given that FreeBSD already has the ability to > use both hardware and software interrupts as sources of entropy. It is relevant because it seems there is entropy available in fine-grained timing.
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