string/FreeBSD/timingsafe_bcmp.3

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  18 .Dd August 15, 2016
  19 .Dt TIMINGSAFE_BCMP 3
  20 .Os
  21 .Sh NAME
  22 .Nm timingsafe_bcmp
  23 .Nd timing-safe byte sequence comparisons
  24 .Sh SYNOPSIS
  25 .In string.h
  26 .Ft int
  27 .Fn timingsafe_bcmp "const void *b1" "const void *b2" "size_t len"
  28 .Sh DESCRIPTION
  29 The
  30 .Fn timingsafe_bcmp
  31 function compares the first
  32 .Fa len
  33 bytes pointed to by
  34 .Fa b1
  35 and
  36 .Fa b2 .
  37 .Pp
  38 Additionally, the running time is independent of the byte sequences compared,
  39 making it safe to use for comparing secret values such as cryptographic MACs.
  40 In contrast,
  41 .Xr bcmp 3
  42 and
  43 .Xr memcmp 3
  44 may short-circuit after finding the first differing byte.
  45 .Sh RETURN VALUES
  46 The
  47 .Fn timingsafe_bcmp
  48 function returns 0 or not zero if the byte sequence pointed to by
  49 .Fa b1
  50 compares equal to or not equal to (respectively)
  51 the byte sequence pointed to by
  52 .Fa b2 .
  53 .Sh SEE ALSO
  54 .Xr bcmp 3
  55 .Sh STANDARDS
  56 The
  57 .Fn timingsafe_bcmp
  58 function is a non-standard extension.
  59 .Sh HISTORY
  60 The
  61 .Fn timingsafe_bcmp
  62 function first appeared in
  63 .Ox 4.9 ,
  64 .Fx 12.0 ,
  65 and macOS 10.12.1.