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TIMINGSAFE_BCMP(3) FreeBSD Library Functions Manual TIMINGSAFE_BCMP(3) NAME timingsafe_bcmp, timingsafe_memcmp - timing-safe byte sequence comparisons SYNOPSIS #include <string.h> int timingsafe_bcmp(const void *b1, const void *b2, size_t len); int timingsafe_memcmp(const void *b1, const void *b2, size_t len); DESCRIPTION The timingsafe_bcmp() and timingsafe_memcmp() functions lexicographically compare the first len bytes (each interpreted as an unsigned char) pointed to by b1 and b2. 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, bcmp(3) and memcmp(3) may short-circuit after finding the first differing byte. RETURN VALUES The timingsafe_bcmp() function returns 0 or not zero if the byte sequence pointed to by b1 compares equal to or not equal to (respectively) the byte sequence pointed to by b2. The timingsafe_memcmp() function returns a negative value, 0, or positive value if the byte sequence pointed to by b1 compares less than, equal to, or greater than (respectively) the byte sequence pointed to by b2. SEE ALSO bcmp(3), memcmp(3) STANDARDS The timingsafe_bcmp() and timingsafe_memcmp() functions are FreeBSD extensions. HISTORY The timingsafe_bcmp() function first appeared in OpenBSD 4.9. The timingsafe_memcmp() function first appeared in OpenBSD 5.6. Both functions first appeared in FreeBSD 12.0. FreeBSD 14.1-RELEASE-p8 August 15, 2016 FreeBSD 14.1-RELEASE-p8