From 55c239d83413d3092c38acde8191d9249cf9f0ee Mon Sep 17 00:00:00 2001 From: Sebastian Huber Date: Fri, 18 Mar 2016 11:49:27 +0100 Subject: Add timingsafe_memcmp() This function is used by LibreSSL and OpenSSH and is provided by the OpenBSD libc. * libc/include/string.h (timingsafe_memcmp): Declare. * libc/string/timingsafe_memcmp.c: New file. * libc/string/Makefile.am: Add new file. * libc/string/Makefile.in: Regenerate. --- newlib/libc/string/timingsafe_memcmp.c | 46 ++++++++++++++++++++++++++++++++++ 1 file changed, 46 insertions(+) create mode 100644 newlib/libc/string/timingsafe_memcmp.c (limited to 'newlib/libc/string/timingsafe_memcmp.c') diff --git a/newlib/libc/string/timingsafe_memcmp.c b/newlib/libc/string/timingsafe_memcmp.c new file mode 100644 index 000000000..04e2ac5e2 --- /dev/null +++ b/newlib/libc/string/timingsafe_memcmp.c @@ -0,0 +1,46 @@ +/* $OpenBSD: timingsafe_memcmp.c,v 1.1 2014/06/13 02:12:17 matthew Exp $ */ +/* + * Copyright (c) 2014 Google Inc. + * + * Permission to use, copy, modify, and distribute this software for any + * purpose with or without fee is hereby granted, provided that the above + * copyright notice and this permission notice appear in all copies. + * + * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES + * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF + * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR + * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES + * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN + * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF + * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. + */ + +#include +#include + +int +timingsafe_memcmp(const void *b1, const void *b2, size_t len) +{ + const unsigned char *p1 = b1, *p2 = b2; + size_t i; + int res = 0, done = 0; + + for (i = 0; i < len; i++) { + /* lt is -1 if p1[i] < p2[i]; else 0. */ + int lt = (p1[i] - p2[i]) >> CHAR_BIT; + + /* gt is -1 if p1[i] > p2[i]; else 0. */ + int gt = (p2[i] - p1[i]) >> CHAR_BIT; + + /* cmp is 1 if p1[i] > p2[i]; -1 if p1[i] < p2[i]; else 0. */ + int cmp = lt - gt; + + /* set res = cmp if !done. */ + res |= cmp & ~done; + + /* set done if p1[i] != p2[i]. */ + done |= lt | gt; + } + + return (res); +} -- cgit v1.2.3