Mercurial > urweb
diff src/c/urweb.c @ 1512:dcc8abbc6dfd
Change cookie signature comparison to resist timing attacks (based on code suggested by Robin Green and Austin Seipp)
author | Adam Chlipala <adam@chlipala.net> |
---|---|
date | Tue, 19 Jul 2011 09:18:50 -0400 |
parents | 7f8ddcf12b20 |
children | 3c0803c1acd7 |
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--- a/src/c/urweb.c Sun Jul 17 14:49:52 2011 -0400 +++ b/src/c/urweb.c Tue Jul 19 09:18:50 2011 -0400 @@ -3455,6 +3455,23 @@ return r; } +/* This bit of crafty code is intended to prevent GCC from performing + * optimizations that would enable timing attacks. See: + * http://www.impredicative.com/pipermail/ur/2011-July/000659.html + */ +int uw_streq(uw_Basis_string s1, uw_Basis_string s2) { + int i, x = 0, len1 = strlen(s1); + + if (len1 != strlen(s2)) return 0; + + for (i = 0; i < len1; ++i) { + __asm__ __volatile__ (""); + x |= s1[i] ^ s2[i]; + } + + return x == 0; +} + uw_Basis_string uw_Basis_sigString(uw_context ctx, uw_unit u) { return ctx->app->cookie_sig(ctx); }