[paramiko] paramiko random number regression: Stop using RandomPool!

[Dwayne Litzenberger]

On April 12, 2008 04:06:27 pm Robey Pointer wrote:
> Is there nothing Windows users can do? I added RandomPool as a
> fallback because on my Windows XP box did not have the winrandom
> module. Since I think XP will be the most widely used Windows release
> for the forseeable future, this is really bad. :(

It has nothing to do with Windows XP.  The winrandom module is part of 
*PyCrypto*, but there is a bug in PyCrypto 2.0.1 where the winrandom module 
is omitted from setup.py.

On Windows systems, the os.urandom function in Python >= 2.4 is equivalent to 
the winrandom.new().get_bytes function.  That's why my previous patch kept 
both os.urandom and /dev/urandom.

In addition to fixing this RNG regression, my latest patch also does several 
other sanity checks to avoid running insecurely, and it combines RandomPool 
with the OS RNG in a thread-safe manner, so that certain types of potential 
weaknesses in the OS RNG don't become immediately exploitable in paramiko.  
Since Microsoft is changing how the Windows RNG works, I think this is a good 
idea.

For the long term, I plan to take over the maintainership of PyCrypto, and 
move this functionality into PyCrypto itself.  (When I contacted A. M. 
Kuchling about the winrandom problem, he said that he's not doing much with 
PyCrypto anymore.  Nobody else seems to be maintaining PyCrypto either, so I 
might as well do it.)  It'll be a month or two before I start making releases 
of PyCrypto; I'm moving across the country at the end of the month, and there 
is a pile of bug reports and suggested changes to PyCrypto that I want to 
sort through before I release anything.  I don't want to risk making things 
worse by rushing a PyCrypto release, but in the meantime, you can improve 
paramiko's security by applying "paramiko-fix-rng-again.bundle".

-- 
Dwayne Litzenberger, B.A.Sc.
Information Technology Analyst

Open Systems Canada Limited
#210 - 2332 11th Ave
Regina, SK S4P0K1
Office: (306) 359-OSCL (6725)
http://www.oscl.ca/
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