The perils of security tools

[IanG]

Steven M. Bellovin wrote:
> On Sat, 24 May 2008 20:29:51 +0100
> Ben Laurie <ben at links.org> wrote:
> 
>> Of course, we have now persuaded even the most stubborn OS that 
>> randomness matters, and most of them make it available, so perhaps
>> this concern is moot.
>>
>> Though I would be interested to know how well they do it! I did have 
>> some input into the design for FreeBSD's, so I know it isn't
>> completely awful, but how do other OSes stack up?
>>
> I believe that all open source Unix-like systems have /dev/random
> and /dev/urandom; Solaris does as well.


Yes, but with different semantics:

      /dev/urandom is a compatibility nod
      to Linux. On Linux, /dev/urandom will
      produce lower quality output if the
      entropy pool drains, while
      /dev/random will prefer to block and
      wait for additional entropy to be
      collected.  With Yarrow, this choice
      and distinction is not necessary,
      and the two devices behave
      identically. You may use either.

(random(4) from Mac OSX.)

Depending on where you are in the security paranoia 
equation, the differences matter little or a lot.  If doing 
medium level security, it's fine to outsource the critical 
components to the OS, and accept any failings.  If doing 
paranoid-level stuff, then best to implement ones own mix 
and just stir in the OS level offering.  That way we reduce 
the surface area for lower-layer config attacks like the 
Debian adventure.

iang

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