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Date: Tue, 1 Jan 2019 11:45:39 -0500
From: Jeffrey Walton <noloader@...il.com>
To: Torbjörn Granlund <tg@...lib.org>
Cc: Niels Möller <nisse@...ator.liu.se>,
oss-security@...ts.openwall.com, gmp-bugs@...lib.org
Subject: Re: Asserts considered harmful (or GMP spills its sensitive information)
On Tue, Jan 1, 2019 at 11:19 AM Torbjörn Granlund <tg@...lib.org> wrote:
>
> The assert that Jeffrey has hit is in sec_powm.c,
>
> ASSERT_ALWAYS (enb >= windowsize);
>
> As far as I can see, "enb" is the input argument to the win_size function,
> and "windowsize" is the return value. I'm waiting for more information,
> since it works fine in my build. Possible explanations I see are
>
> A reasonable assumption is that this user has modified the sources to
> cause this bug. The motive would be to support his auxesis about how
> insecure GMP is.
My bad, I did not mean to imply this was a problem with GMP only. GMP
has a lot of company, like GnuPG and OpenSSL.
I believe the assumption is incorrect. The sources were not modified,
and a standard (?) 'configure; make; make check' was used. The
reproducer script is available at
https://www.openwall.com/lists/oss-security/2018/12/31/1; see
test-gmp.sh.txt.
For completeness here's a quick audit of some security libraries.
Botan, Crypto++ and OpenSSL use -DNDEBUG to remove asserts from
production/release builds. They use asserts as a debugging/diagnostic
aide. They don't depend on crashing the program and risk egressing
sensitive information outside the app's security boundary.
gmp-6.1.2$ grep -iIR assert | wc -l
4867
openssl-1.0.2$ grep -iIR assert | wc -l
436
libgcrypt-1.8.4$ grep -iIR assert | wc -l
245
gnupg-2.2.12$ grep -iIR assert | wc -l
1337
cryptopp-8.0$ grep -iIR assert | wc -l
1123
botan-2.8$ grep -iIR assert | wc -l
746
Cheers, Jeff
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