BN_zero(3)

BN_zero(3) | OpenSSL | BN_zero(3)

# NAME

BN_zero, BN_one, BN_value_one, BN_set_word, BN_get_word - BIGNUM assignment operations

# SYNOPSIS

     #include <openssl/bn.h>
     void BN_zero(BIGNUM *a);
     int BN_one(BIGNUM *a);
     const BIGNUM *BN_value_one(void);
     int BN_set_word(BIGNUM *a, BN_ULONG w);
     unsigned BN_ULONG BN_get_word(BIGNUM *a);

# DESCRIPTION

BN_ULONG is a macro that will be an unsigned integral type optimized for the most efficient implementation on the local platform.

BN_zero(), BN_one() and BN_set_word() set a to the values 0, 1 and w respectively. BN_zero() and BN_one() are macros.

BN_value_one() returns a BIGNUM constant of value 1. This constant is useful for use in comparisons and assignment.

BN_get_word() returns a, if it can be represented as a BN_ULONG.

# RETURN VALUES

BN_get_word() returns the value a, or all-bits-set if a cannot be represented as a single integer.

BN_one() and BN_set_word() return 1 on success, 0 otherwise. BN_value_one() returns the constant. BN_zero() never fails and returns no value.

# BUGS

If a BIGNUM is equal to the value of all-bits-set, it will collide with the error condition returned by BN_get_word() which uses that as an error value.

BN_ULONG should probably be a typedef.

# SEE ALSO

BN_bn2bin(3)

# HISTORY

In OpenSSL 0.9.8, BN_zero() was changed to not return a value; previous versions returned an int.

# COPYRIGHT

Copyright 2000-2018 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the Apache License 2.0 (the "License"). You may not use this file except in compliance with the License. You can obtain a copy in the file LICENSE in the source distribution or at <https://www.openssl.org/source/license.html>.

2026-06-09 | 3.5.7