1.\" $OpenBSD: timingsafe_bcmp.3,v 1.2 2014/06/21 20:22:15 tedu Exp $ 2.\" 3.\" Copyright (c) 2014 Google Inc. 4.\" 5.\" Permission to use, copy, modify, and distribute this software for any 6.\" purpose with or without fee is hereby granted, provided that the above 7.\" copyright notice and this permission notice appear in all copies. 8.\" 9.\" THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES 10.\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF 11.\" MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR 12.\" ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES 13.\" WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN 14.\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF 15.\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. 16.\" 17.\" $FreeBSD$ 18.Dd August 15, 2016 19.Dt TIMINGSAFE_BCMP 3 20.Os 21.Sh NAME 22.Nm timingsafe_bcmp , 23.Nm timingsafe_memcmp 24.Nd timing-safe byte sequence comparisons 25.Sh SYNOPSIS 26.In string.h 27.Ft int 28.Fn timingsafe_bcmp "const void *b1" "const void *b2" "size_t len" 29.Ft int 30.Fn timingsafe_memcmp "const void *b1" "const void *b2" "size_t len" 31.Sh DESCRIPTION 32The 33.Fn timingsafe_bcmp 34and 35.Fn timingsafe_memcmp 36functions lexicographically compare the first 37.Fa len 38bytes (each interpreted as an 39.Vt unsigned char ) 40pointed to by 41.Fa b1 42and 43.Fa b2 . 44.Pp 45Additionally, their running times are independent of the byte sequences compared, 46making them safe to use for comparing secret values such as cryptographic MACs. 47In contrast, 48.Xr bcmp 3 49and 50.Xr memcmp 3 51may short-circuit after finding the first differing byte. 52.Sh RETURN VALUES 53The 54.Fn timingsafe_bcmp 55function returns 0 or not zero if the byte sequence pointed to by 56.Fa b1 57compares equal to or not equal to (respectively) 58the byte sequence pointed to by 59.Fa b2 . 60.Pp 61The 62.Fn timingsafe_memcmp 63function returns a negative value, 0, or positive value if the byte sequence 64pointed to by 65.Fa b1 66compares less than, equal to, or greater than (respectively) 67the byte sequence pointed to by 68.Fa b2 . 69.Sh SEE ALSO 70.Xr bcmp 3 , 71.Xr memcmp 3 72.Sh STANDARDS 73The 74.Fn timingsafe_bcmp 75and 76.Fn timingsafe_memcmp 77functions are 78.Fx 79extensions. 80.Sh HISTORY 81The 82.Fn timingsafe_bcmp 83function first appeared in 84.Ox 4.9 . 85.Pp 86The 87.Fn timingsafe_memcmp 88function first appeared in 89.Ox 5.6 . 90.Pp 91Both functions first appeared in 92.Fx 12.0 . 93