Date: Wed, 13 Sep 2017 10:34:34 -0600 From: Ian Lepore <ian@freebsd.org> To: "freebsd-arch@FreeBSD.org" <freebsd-arch@FreeBSD.org> Subject: hardware RNG harvest rate Message-ID: <1505320474.32063.120.camel@freebsd.org>
next in thread | raw e-mail | index | archive | help
While looking into updating the hardware rng driver for RPi 3 I discovered that on the original wimpy RPi we're feeding random_harvest_queue() with 16 bytes of generated data, 82 times a second. That seems like a lot of work for a wimpy processor, and probably more than needed for good random numbers. I looked at some other rng drivers, and I see them feeding in a few bytes at a time at rates ranging from 100 Hz to once every 5 seconds. So no clear concensus there. Some have this comment: /* MarkM: FIX!! Check that this does not swamp the harvester! */ A comment block above random_harvest_queue() warns, in part: * It is also illegal (and morally reprehensible) to insert any * high-rate data here. So is there any simple "X bytes per second is good and more than Y is wasted/harmful" advice available? -- Ian
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?1505320474.32063.120.camel>