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bug#22202: 24.5; SECURITY ISSUE -- Emacs Server vulnerable to random num

From: Richard Copley
Subject: bug#22202: 24.5; SECURITY ISSUE -- Emacs Server vulnerable to random number generator attack on Windows systems
Date: Thu, 31 Dec 2015 19:49:42 +0000

>> That last patch would still improve matters. The user would have
>> to be publishing the output of their PRNG to begin with in order
>> for the attacker to analyse it and guess the seed. (I don't know
>> how one could do that but that's no proof that it's impossible.)
>I don't even understand how that could be possible.

Me either, but that doesn't make it impossible. (There are articles
on the web demonstrating such feats, if you're interested.)

>> What Demetri has just described is what I would do.
>Now I'm confused: do what?

As I understand it: Provide a function callable from lisp that returns
a cryptographically secure sequence of random bytes, of a specified
length. Use that function to generate the server secret.

>We still need to support 'random' with an
>argument, so we cannot get rid of seeding a PRNG with a known value.
>And I didn't want to remove srandom.

Given the above, we could leave "random", etc., as they are, or we
could use a better PRNG and/or seed with system entropy. It would
no longer be tied up with this issue report.

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