Re: [boost] [xint] Boost.XInt formal review

Subject: Re: [boost] [xint] Boost.XInt formal review
From: Chad Nelson (chad.thecomfychair_at_[hidden])
Date: 2011-03-05 14:13:03

On Fri, 4 Mar 2011 09:36:03 -0800
"Dick Bridges" <Dick.Bridges_at_[hidden]> wrote:

>>> As long as I'm asking, perhaps the ability to provide a
>>> special-purpose generator of our own design?
>> 
>> You already can. :-) The random.hpp classes are there only for
>> convenience. In all of the few functions that use a random generator,
>> you can substitute any Boost.Random generator class, or any other
>> class that has a similar interface. If you've got specialized
>> random-number- generating hardware, the code will happily work with
>> it, with nothing extra but a simple interface class.
> </snip>
>
> If I might make a suggestion, the XInt library interface could be
> simplified by removing all notions of RNG quality (strong, random,
> etc.) and become more in line with the goal of providing a POD-like
> data type.

Yes, but it would require pulling Boost.Random into the example code,
which would complicate it.

> On an abstract [carefully avoiding 'generic'] level, an RNG is an RNG
> is an RNG. One of the problems I see with syntactic candy like
> 'strong_random_generator' is that it implies the generated values are
> both cryptographically acceptable and actually random (and verified
> by the library). IIUC, there is nothing in the library that attempts
> to verify either.

The Windows implementation uses the formerly-undocumented RtlGenRandom
function, which is what Microsoft's own cryptography library relies on
for random numbers. The POSIX implementation uses /dev/urandom, which
has well-known strengths and limitations. As an amateur cryptographer,
I consider the silence of professional cryptographers on their
strengths to be proof enough that they're sufficiently
cryptographically strong for most uses. Especially considering the
uproar from them a few years ago when a coding mistake made the Debian
distribution's generator much weaker for a while.

> IMHO, the XInt library should make no pretense wrt RNG quality - let
> the user specify the RNG or use the default (as is now provided by
> default_random_generator).

The user can, and in fact must. The default_random_generator was truly
a default in earlier iterations of the library, but neither of those
classes are used for anything except the example code now.
-- 
Chad Nelson
Oak Circle Software, Inc.
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