Date: Sun, 6 Jan 2019 10:39:50 -0500 From: Jeffrey Walton <noloader@...il.com> To: Niels Möller <nisse@...ator.liu.se> Cc: oss-security@...ts.openwall.com, gmp-bugs@...lib.org Subject: Re: Asserts considered harmful (or GMP spills its sensitive information) On Sun, Jan 6, 2019 at 5:31 AM Niels Möller <nisse@...ator.liu.se> wrote: > > tg@...lib.org (Torbjörn Granlund) writes: > > > Let's move on. No bug to be found here. > > Just FYI: There was a bug in Nettle's test code, a line > > assert (mpz_invert(key->d, pub->e, phi)); > > Obviously not working with -DNDEBUG. Fix in commit > https://git.lysator.liu.se/nettle/nettle/commit/73d3c6d5586cc0fd81eab081078144d621de07b4 A small suggestion to remove the sharp edge. If using -DNDEBUG is not supported, then fail configure when it is present. Something like the following in configure.ac should work well: BAD_OPT=`echo $CFLAGS | $EGREP -c '\-DNDEBUG` if test "$BAD_OPT" != "0"; then AC_MSG_ERROR (...) fi And as a safety net, maybe something in the source code like: #if defined(NDEBUG) || defined(_NDEBUG) # error NDEBUG is not supported #endif There are two reasons for the suggestion. First, RTFM does not work. If it was going to work, then it should have happened in the last 50 years or so. Gutmann provides the user psychology behind it in his Security Engineering book, https://www.cs.auckland.ac.nz/~pgut001/pubs/book.pdf . Second, folks who have a Windows programming background use -NDEBUG. It is a standard practice and not a one-off problem. The issue should surface again for two use cases. First, Windows programmers working on Unix and Linux. Second, Windows programmers who are porting projects to Windows. Jeff
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