[wha...@lists.whatwg.org removed from cc list because I'm not on
it and MarkM suggested dropping it.]
On 2/14/11 at 4:20 PM, sha...@google.com (Shabsi Walfish) wrote:
Hmm... if there is a guarantee that /dev/urandom was successfully seeded at
some point in the past, then I'm happy with it. Is there such a guarantee? I
don't see that documented anywhere, and I'm not sure how it would be
provided. Since /dev/urandom never blocks, I'm assuming it will return
something based mostly on weak entropy sources (like system time and/or or a
very small number of real bits of entropy) in the event that the system
hasn't really had a chance to seed the pool yet. I can live with not
reliably refreshing the pool, but its pretty scary if you think about what
happens when a user boots their phone up for the first time, etc. and there
is just no entropy there yet.
While I think this question is a bit outside the language area,
as an OS person, it falls directly in my lap, so please indulge
me while I pontificate.
Getting unguessable bits into a deterministic system like a
computer is very platform dependent. Disk timing, variable
because of air turbulence on the platters, has been a popular
source. However now many systems have solid state disks. This
dependency means we are at the mercy of the system builders.
I don't know that there are any guarantees. Consider the environments:
Servers
pcs
phones/tablets
(others?)
I think the worst case is servers. They live in a temperature
controlled room, and the only I/O they have is a network
connection and a disk farm. With some luck, the server operator
will have a source of unguessable bits included on a crypto
board or on one of the manufacture's support chips. Otherwise
there's timings on the disk and network I/O. A number of the CPU
chips have "cycle counter" which can provide high resolution
timing for interrupts etc.
Pcs (lower case because I mean it generically) have a number of
good sources involved with UI events, microphones etc. There is
time between boot and first application launch to gather mouse
movements, ambient sound etc.
Phones/tablets have a wonderful set of resources: radio noise,
compass direction, GPS location tracking, microphone input,
camera input, etc. They should be able to get enough unguessable
bits within a few seconds, certainly by the time they've
established network connectivity.
Cheers - Bill
-----------------------------------------------------------------------
Bill Frantz | gets() remains as a monument | Periwinkle
(408)356-8506 | to C's continuing support of | 16345
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www.pwpconsult.com | buffer overruns. | Los Gatos,
CA 95032
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