Showing Revision 1 created 04/27/2012 by Amara Bot.

1. Title:
   02-07 Sources Of Randomness
2. Description:

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   And Quantum Mechanics provides a notion of random events
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   --that there are events in the universe that are inherently random--
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   and we can count things like radioactive decay with a Geiger counter
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   and use that to generate randomness from physical events.
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   Thermal noise is an easier thing to measure in most circumstances.
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   If you can measure that precisely enough--it also depends on Quantum Mechanics--
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   at some level and produces randomness.
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    And many modern processors have a way of generating a small amount
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    of randomness by measuring thermal noise in the processor.
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    Whether it's really physically random depends on a lot of other things.
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    You can also look at things that actually happen, and think that
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    they are random. Maybe if they're key presses or user actions--
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    maybe those are random. An example of this is when we generate
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    a new key using GPG, it will ask you to generate
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    --when you start to generate a key--it says we need lots of random bytes
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    and you can perform some type of action like moving the mouse using the disc
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    to help generate more randomness for it.
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    And humans aren't good at doing random stuff
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    When we move the mouse, we're probably moving it in a pattern--
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    When we type on the keyboard, maybe we're doing things
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    that are not very random. So unless you're generating your randomness from
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    quantum physics, there's always some question whether it's really random enough.
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    Or whether you can predict the particular motions I took. And certainly
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    given that this has been recorded and released, the fake key that I generated
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    for Alyssa B. Hacker should not be used for any secure purpose.
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    So this approach of waiting for physically random events
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    is OK for GPG, maybe, because someone using it is
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    probably patient enough to sit around for a while, doing random stuff
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    as well as a human can to generate a key.
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    This would not work very well when you need more randomness
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    more quickly. And this happens every time you do a web transaction.
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    Every time someone does a secure web session,
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    any time you see the lock key in your browser,
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    there's a protocol going on called TLS. We'll talk about that more in a later unit.
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    But one thing that that requires is a new random key.
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    for each secure web session.
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    I don't think many people would tolerate being asked to move around their mouse
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    and do strange things to generate enough randomness in the hopes that
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    that key is secure every time you connect to a website.
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    So we need something better. We need a way to take a little bit
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    of physical randomness, and that's usually known as the seed--
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    that's the initial state, and that's the input to what's known
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    as a pseudo-random number generator. And that produces
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    a long sequence--that is longer than the amount of physical randomness
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    we started with--of random bits.
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    So that's our goal--to take a small amount of physical randomness
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    --some source of entropy that we can use as a seed--
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    have some function that will compute from that seed a long sequence
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    of apparently random bits.