consttime_memequal(3) - NetBSD Manual Pages

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CONSTTIME_MEMEQUAL(3)   NetBSD Library Functions Manual  CONSTTIME_MEMEQUAL(3)


NAME

     consttime_memequal -- compare byte strings for equality without timing
     leaks


LIBRARY

     Standard C Library (libc, -lc)


SYNOPSIS

     #include <string.h>

     int
     consttime_memequal(void *b1, void *b2, size_t len);


DESCRIPTION

     The consttime_memequal() function compares len bytes of memory at b1 and
     b2 for equality, returning 0 if they are distinct and 1 if they are iden-
     tical.

     The time taken by consttime_memequal() depends on len, but not on the
     data at b1 or b2.  Thus, consttime_memequal() is appropriate for compar-
     ing cryptographic secrets, hashes, message authentication codes, etc.,
     without leaking information about them through a timing side channel.  In
     crypto literature, consttime_memequal() is said to take `constant time',
     meaning time that does not vary depending on the data it processes.

     Note that unlike memcmp(3), consttime_memequal() does not return a lexi-
     cographic ordering on the data at b1 and b2; it tells only whether they
     are equal.  NetBSD does not provide a consttime_memcmp() function,
     because all known use cases that require `constant time' memory compari-
     son also require only comparison for equality, not lexicographic order-
     ing.


SEE ALSO

     explicit_memset(3), memcmp(3)


HISTORY

     The consttime_memequal() function appeared in NetBSD 7.0.

NetBSD 9.0                      March 23, 2015                      NetBSD 9.0