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Add timingsafe_memcmp().

ok deraadt, jmc, tedu
OPENBSD_5_6
matthew 10 years ago
parent
commit
f82197f5b3
6 changed files with 154 additions and 34 deletions
  1. +2
    -1
      src/include/string.h
  2. +6
    -5
      src/lib/libc/string/Makefile.inc
  3. +5
    -26
      src/lib/libc/string/bcmp.3
  4. +3
    -2
      src/lib/libc/string/memcmp.3
  5. +92
    -0
      src/lib/libc/string/timingsafe_bcmp.3
  6. +46
    -0
      src/lib/libc/string/timingsafe_memcmp.c

+ 2
- 1
src/include/string.h View File

@ -1,4 +1,4 @@
/* $OpenBSD: string.h,v 1.27 2014/01/22 21:06:45 tedu Exp $ */
/* $OpenBSD: string.h,v 1.28 2014/06/13 02:12:17 matthew Exp $ */
/* $NetBSD: string.h,v 1.6 1994/10/26 00:56:30 cgd Exp $ */ /* $NetBSD: string.h,v 1.6 1994/10/26 00:56:30 cgd Exp $ */
/*- /*-
@ -138,6 +138,7 @@ size_t strlcpy(char *, const char *, size_t)
void strmode(int, char *); void strmode(int, char *);
char *strsep(char **, const char *); char *strsep(char **, const char *);
int timingsafe_bcmp(const void *, const void *, size_t); int timingsafe_bcmp(const void *, const void *, size_t);
int timingsafe_memcmp(const void *, const void *, size_t);
#endif #endif
__END_DECLS __END_DECLS


+ 6
- 5
src/lib/libc/string/Makefile.inc View File

@ -1,4 +1,4 @@
# $OpenBSD: Makefile.inc,v 1.34 2014/03/23 23:16:48 tedu Exp $
# $OpenBSD: Makefile.inc,v 1.35 2014/06/13 02:12:17 matthew Exp $
# string sources # string sources
.PATH: ${LIBCSRCDIR}/arch/${MACHINE_CPU}/string ${LIBCSRCDIR}/string .PATH: ${LIBCSRCDIR}/arch/${MACHINE_CPU}/string ${LIBCSRCDIR}/string
@ -7,11 +7,11 @@ SRCS+= explicit_bzero.c memccpy.c memmem.c memrchr.c stpcpy.c stpncpy.c \
strcasecmp.c strcasestr.c strcoll.c strdup.c \ strcasecmp.c strcasestr.c strcoll.c strdup.c \
strerror.c strerror_r.c strlcat.c strmode.c strndup.c strnlen.c \ strerror.c strerror_r.c strlcat.c strmode.c strndup.c strnlen.c \
strsignal.c strtok.c strxfrm.c \ strsignal.c strtok.c strxfrm.c \
timingsafe_bcmp.c timingsafe_memcmp.c \
wcscat.c wcschr.c wcscmp.c wcscpy.c wcscspn.c wcslcat.c wcslcpy.c \ wcscat.c wcschr.c wcscmp.c wcscpy.c wcscspn.c wcslcat.c wcslcpy.c \
wcslen.c wcsncat.c wcsncmp.c wcsncpy.c wcspbrk.c wcsrchr.c wcsspn.c \ wcslen.c wcsncat.c wcsncmp.c wcsncpy.c wcspbrk.c wcsrchr.c wcsspn.c \
wcsstr.c wcstok.c wcswcs.c wcswidth.c wmemchr.c wmemcmp.c wmemcpy.c \ wcsstr.c wcstok.c wcswcs.c wcswidth.c wmemchr.c wmemcmp.c wmemcpy.c \
wmemmove.c wmemset.c wcsdup.c \
timingsafe_bcmp.c wcscasecmp.c
wmemmove.c wmemset.c wcsdup.c wcscasecmp.c
# machine-dependent net sources # machine-dependent net sources
# m-d Makefile.inc must include sources for: # m-d Makefile.inc must include sources for:
@ -149,7 +149,8 @@ MAN+= bcmp.3 bcopy.3 bstring.3 bzero.3 ffs.3 memccpy.3 memchr.3 \
strcat.3 strchr.3 strcmp.3 strcoll.3 strcpy.3 strcspn.3 strdup.3 \ strcat.3 strchr.3 strcmp.3 strcoll.3 strcpy.3 strcspn.3 strdup.3 \
strerror.3 string.3 strlen.3 strmode.3 strncat.3 strncpy.3 strpbrk.3 \ strerror.3 string.3 strlen.3 strmode.3 strncat.3 strncpy.3 strpbrk.3 \
strrchr.3 strsep.3 strsignal.3 strspn.3 strstr.3 strtok.3 strxfrm.3 \ strrchr.3 strsep.3 strsignal.3 strspn.3 strstr.3 strtok.3 strxfrm.3 \
swab.3 strlcpy.3 wcscasecmp.3 wcscat.3 wcschr.3 wcscmp.3 wcscpy.3 \
swab.3 strlcpy.3 timingsafe_bcmp.3 \
wcscasecmp.3 wcscat.3 wcschr.3 wcscmp.3 wcscpy.3 \
wcscspn.3 wcsdup.3 wcslcpy.3 wcslen.3 wcspbrk.3 wcsrchr.3 wcsspn.3 \ wcscspn.3 wcsdup.3 wcslcpy.3 wcslen.3 wcspbrk.3 wcsrchr.3 wcsspn.3 \
wcsstr.3 wcstok.3 wcswidth.3 wmemchr.3 wmemcmp.3 wmemcpy.3 wmemmove.3 \ wcsstr.3 wcstok.3 wcswidth.3 wmemchr.3 wmemcmp.3 wmemcpy.3 wmemmove.3 \
wmemset.3 wmemset.3
@ -167,9 +168,9 @@ MLINKS+=strlen.3 strnlen.3
MLINKS+=strstr.3 strcasestr.3 MLINKS+=strstr.3 strcasestr.3
MLINKS+=strtok.3 strtok_r.3 MLINKS+=strtok.3 strtok_r.3
MLINKS+=strerror.3 strerror_r.3 MLINKS+=strerror.3 strerror_r.3
MLINKS+=timingsafe_bcmp.3 timingsafe_memcmp.3
MLINKS+=wcscasecmp.3 wcsncasecmp.3 MLINKS+=wcscasecmp.3 wcsncasecmp.3
MLINKS+=wcscat.3 wcsncat.3 MLINKS+=wcscat.3 wcsncat.3
MLINKS+=wcscmp.3 wcsncmp.3 MLINKS+=wcscmp.3 wcsncmp.3
MLINKS+=wcscpy.3 wcsncpy.3 MLINKS+=wcscpy.3 wcsncpy.3
MLINKS+=wcslcpy.3 wcslcat.3 MLINKS+=wcslcpy.3 wcslcat.3
MLINKS+=bcmp.3 timingsafe_bcmp.3

+ 5
- 26
src/lib/libc/string/bcmp.3 View File

@ -27,21 +27,18 @@
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE. .\" SUCH DAMAGE.
.\" .\"
.\" $OpenBSD: bcmp.3,v 1.10 2013/06/05 03:39:23 tedu Exp $
.\" $OpenBSD: bcmp.3,v 1.11 2014/06/13 02:12:17 matthew Exp $
.\" .\"
.Dd $Mdocdate: June 5 2013 $
.Dd $Mdocdate: June 13 2014 $
.Dt BCMP 3 .Dt BCMP 3
.Os .Os
.Sh NAME .Sh NAME
.Nm bcmp ,
.Nm timingsafe_bcmp
.Nm bcmp
.Nd compare byte string .Nd compare byte string
.Sh SYNOPSIS .Sh SYNOPSIS
.In string.h .In string.h
.Ft int .Ft int
.Fn bcmp "const void *b1" "const void *b2" "size_t len" .Fn bcmp "const void *b1" "const void *b2" "size_t len"
.Ft int
.Fn timingsafe_bcmp "const void *b1" "const void *b2" "size_t len"
.Sh DESCRIPTION .Sh DESCRIPTION
The The
.Fn bcmp .Fn bcmp
@ -56,33 +53,15 @@ bytes long.
Zero-length strings are always identical. Zero-length strings are always identical.
.Pp .Pp
The strings may overlap. The strings may overlap.
.Pp
The
.Fn timingsafe_bcmp
function has the same semantics as
.Fn bcmp ,
but its running time is independent of the contents of
.Fa b1
and
.Fa b2 ,
making it safe to use for comparing secret values such as cryptographic MACs.
In contrast,
.Fn bcmp
returns after finding the first differing byte,
making it vulnerable to timing attacks.
.Sh SEE ALSO .Sh SEE ALSO
.Xr memcmp 3 , .Xr memcmp 3 ,
.Xr strcasecmp 3 , .Xr strcasecmp 3 ,
.Xr strcmp 3 , .Xr strcmp 3 ,
.Xr strcoll 3 , .Xr strcoll 3 ,
.Xr strxfrm 3
.Xr strxfrm 3 ,
.Xr timingsafe_bcmp 3
.Sh HISTORY .Sh HISTORY
The The
.Fn bcmp .Fn bcmp
function first appeared in function first appeared in
.Bx 4.2 . .Bx 4.2 .
.Pp
The
.Fn timingsafe_bcmp
function first appeared in
.Ox 4.9 .

+ 3
- 2
src/lib/libc/string/memcmp.3 View File

@ -1,4 +1,4 @@
.\" $OpenBSD: memcmp.3,v 1.8 2013/06/05 03:39:23 tedu Exp $
.\" $OpenBSD: memcmp.3,v 1.9 2014/06/13 02:12:17 matthew Exp $
.\" .\"
.\" Copyright (c) 1990, 1991 The Regents of the University of California. .\" Copyright (c) 1990, 1991 The Regents of the University of California.
.\" All rights reserved. .\" All rights reserved.
@ -31,7 +31,7 @@
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE. .\" SUCH DAMAGE.
.\" .\"
.Dd $Mdocdate: June 5 2013 $
.Dd $Mdocdate: June 13 2014 $
.Dt MEMCMP 3 .Dt MEMCMP 3
.Os .Os
.Sh NAME .Sh NAME
@ -70,6 +70,7 @@ Zero-length strings are always identical.
.Xr strcmp 3 , .Xr strcmp 3 ,
.Xr strcoll 3 , .Xr strcoll 3 ,
.Xr strxfrm 3 , .Xr strxfrm 3 ,
.Xr timingsafe_memcmp 3 ,
.Xr wmemcmp 3 .Xr wmemcmp 3
.Sh STANDARDS .Sh STANDARDS
The The


+ 92
- 0
src/lib/libc/string/timingsafe_bcmp.3 View File

@ -0,0 +1,92 @@
.\" $OpenBSD: timingsafe_bcmp.3,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.
.Dd $Mdocdate: June 13 2014 $
.Dt TIMINGSAFE_BCMP 3
.Os
.Sh NAME
.Nm timingsafe_bcmp ,
.Nm timingsafe_memcmp
.Nd timing-safe byte sequence comparisons
.Sh SYNOPSIS
.In string.h
.Ft int
.Fn timingsafe_bcmp "const void *b1" "const void *b2" "size_t len"
.Ft int
.Fn timingsafe_memcmp "const void *b1" "const void *b2" "size_t len"
.Sh DESCRIPTION
The
.Fn timingsafe_bcmp
and
.Fn timingsafe_memcmp
functions lexicographically compare the first
.Fa len
bytes (each interpreted as an
.Vt unsigned char )
pointed to by
.Fa b1
and
.Fa b2 .
.Pp
Additionally, their running times are independent of the byte sequences compared,
making them safe to use for comparing secret values such as cryptographic MACs.
In contrast,
.Xr bcmp 3
and
.Xr memcmp 3
may short-circuit after finding the first differing byte.
.Sh RETURN VALUES
The
.Fn timingsafe_bcmp
function returns 0 or 1 if the byte sequence pointed to by
.Fa b1
compares equal to or not equal to (respectively)
the byte sequence pointed to by
.Fa b2 .
.Pp
The
.Fn timingsafe_memcmp
function returns \-1, 0, or 1 if the byte sequence pointed to by
.Fa b1
compares less than, equal to, or greater than (respectively)
the byte sequence pointed to by
.Fa b2 .
.Pp
Note that these return values are compatible with, but stricter than,
the ones specified for
.Xr bcmp 3
and
.Xr memcmp 3 .
.Sh SEE ALSO
.Xr bcmp 3 ,
.Xr memcmp 3
.Sh STANDARDS
The
.Fn timingsafe_bcmp
and
.Fn timingsafe_memcmp
functions are
.Ox
extensions.
.Sh HISTORY
The
.Fn timingsafe_bcmp
function first appeared in
.Ox 4.9 .
.Pp
The
.Fn timingsafe_memcmp
function first appeared in
.Ox 5.6 .

+ 46
- 0
src/lib/libc/string/timingsafe_memcmp.c View File

@ -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 <limits.h>
#include <string.h>
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);
}

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