.\" $OpenBSD: CRYPTO_memcmp.3,v 1.1 2019/08/25 06:20:22 schwarze Exp $
.\" full merge up to: OpenSSL 1075139c Jun 24 09:18:48 2019 +1000
.\"
.\" This file was written by Pauli <paul.dale@oracle.com>.
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.Dd $Mdocdate: August 25 2019 $
.Dt CRYPTO_MEMCMP 3
.Os
.Sh NAME
.Nm CRYPTO_memcmp
.Nd constant time memory comparison
.Sh SYNOPSIS
.In openssl/crypto.h
.Ft int
.Fo CRYPTO_memcmp
.Fa "const void *a"
.Fa "const void *b"
.Fa "size_t len"
.Fc
.Sh DESCRIPTION
.Fn CRYPTO_memcmp
compares the
.Fa len
bytes pointed to by
.Fa a
and
.Fa b
for equality.
It takes an amount of time dependent on
.Fa len ,
but independent of the contents of the memory regions pointed to by
.Fa a
and
.Fa b .
.Sh RETURN VALUES
.Fn CRYPTO_memcmp
returns 0 if the content of the memory regions is equal
or non-zero otherwise.
.Sh HISTORY
.Fn CRYPTO_memcmp
first appeared in OpenSSL 1.0.1d and has been available since
.Ox 5.6 .
.Sh BUGS
Unlike
.Xr memcmp 3
and
.Xr timingsafe_memcmp 3 ,
this function cannot be used to order the two memory regions.
In the current implementation, the return value is always greater
than or equal to 0.