diff options
Diffstat (limited to 'lib/libc/string/bcmp.3')
| -rw-r--r-- | lib/libc/string/bcmp.3 | 28 |
1 files changed, 25 insertions, 3 deletions
diff --git a/lib/libc/string/bcmp.3 b/lib/libc/string/bcmp.3 index 57e1a0faded..1a777506276 100644 --- a/lib/libc/string/bcmp.3 +++ b/lib/libc/string/bcmp.3 @@ -27,18 +27,21 @@ .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF .\" SUCH DAMAGE. .\" -.\" $OpenBSD: bcmp.3,v 1.7 2007/05/31 19:19:32 jmc Exp $ +.\" $OpenBSD: bcmp.3,v 1.8 2010/09/24 13:33:00 matthew Exp $ .\" -.Dd $Mdocdate: May 31 2007 $ +.Dd $Mdocdate: September 24 2010 $ .Dt BCMP 3 .Os .Sh NAME -.Nm bcmp +.Nm bcmp , +.Nm timingsafe_bcmp .Nd compare byte string .Sh SYNOPSIS .Fd #include <string.h> .Ft int .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 The .Fn bcmp @@ -53,6 +56,20 @@ bytes long. Zero-length strings are always identical. .Pp 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 .Xr memcmp 3 , .Xr strcasecmp 3 , @@ -64,3 +81,8 @@ A .Fn bcmp function first appeared in .Bx 4.2 . +.Pp +The +.Fn timingsafe_bcmp +function first appeared in +.Ox 4.9 . |