## table of contents

BN_BN2BIN(3SSL) | OpenSSL | BN_BN2BIN(3SSL) |

# NAME¶

BN_bn2binpad, BN_bn2bin, BN_bin2bn, BN_bn2lebinpad, BN_lebin2bn, BN_bn2hex, BN_bn2dec, BN_hex2bn, BN_dec2bn, BN_print, BN_print_fp, BN_bn2mpi, BN_mpi2bn - format conversions

# SYNOPSIS¶

#include <openssl/bn.h> int BN_bn2bin(const BIGNUM *a, unsigned char *to); int BN_bn2binpad(const BIGNUM *a, unsigned char *to, int tolen); BIGNUM *BN_bin2bn(const unsigned char *s, int len, BIGNUM *ret); int BN_bn2lebinpad(const BIGNUM *a, unsigned char *to, int tolen); BIGNUM *BN_lebin2bn(const unsigned char *s, int len, BIGNUM *ret); char *BN_bn2hex(const BIGNUM *a); char *BN_bn2dec(const BIGNUM *a); int BN_hex2bn(BIGNUM **a, const char *str); int BN_dec2bn(BIGNUM **a, const char *str); int BN_print(BIO *fp, const BIGNUM *a); int BN_print_fp(FILE *fp, const BIGNUM *a); int BN_bn2mpi(const BIGNUM *a, unsigned char *to); BIGNUM *BN_mpi2bn(unsigned char *s, int len, BIGNUM *ret);

# DESCRIPTION¶

**BN_bn2bin()** converts the absolute value of **a** into
big-endian form and stores it at **to**. **to** must point to
BN_num_bytes(**a**) bytes of memory.

**BN_bn2binpad()** also converts the absolute value of **a**
into big-endian form and stores it at **to**. **tolen** indicates the
length of the output buffer **to**. The result is padded with zeros if
necessary. If **tolen** is less than BN_num_bytes(**a**) an error is
returned.

**BN_bin2bn()** converts the positive integer in big-endian
form of length **len** at **s** into a **BIGNUM** and places it in
**ret**. If **ret** is NULL, a new **BIGNUM** is created.

**BN_bn2lebinpad()** and **BN_lebin2bn()** are identical to
**BN_bn2binpad()** and **BN_bin2bn()** except the buffer is in
little-endian format.

**BN_bn2hex()** and **BN_bn2dec()** return printable strings
containing the hexadecimal and decimal encoding of **a** respectively.
For negative numbers, the string is prefaced with a leading '-'. The string
must be freed later using **OPENSSL_free()**.

**BN_hex2bn()** takes as many characters as possible from the
string **str**, including the leading character '-' which means negative,
to form a valid hexadecimal number representation and converts them to a
**BIGNUM** and stores it in ****a**. If ***a** is NULL, a new
**BIGNUM** is created. If **a** is NULL, it only computes the length
of valid representation. A "negative zero" is converted to zero.
**BN_dec2bn()** is the same using the decimal system.

**BN_print()** and **BN_print_fp()** write the hexadecimal
encoding of **a**, with a leading '-' for negative numbers, to the
**BIO** or **FILE** **fp**.

**BN_bn2mpi()** and **BN_mpi2bn()** convert **BIGNUM**s
from and to a format that consists of the number's length in bytes
represented as a 4-byte big-endian number, and the number itself in
big-endian format, where the most significant bit signals a negative number
(the representation of numbers with the MSB set is prefixed with null
byte).

**BN_bn2mpi()** stores the representation of **a** at
**to**, where **to** must be large enough to hold the result. The size
can be determined by calling BN_bn2mpi(**a**, NULL).

**BN_mpi2bn()** converts the **len** bytes long
representation at **s** to a **BIGNUM** and stores it at **ret**,
or in a newly allocated **BIGNUM** if **ret** is NULL.

# RETURN VALUES¶

**BN_bn2bin()** returns the length of the big-endian number
placed at **to**. **BN_bin2bn()** returns the **BIGNUM**, NULL on
error.

**BN_bn2binpad()** returns the number of bytes written or -1 if
the supplied buffer is too small.

**BN_bn2hex()** and **BN_bn2dec()** return a null-terminated
string, or NULL on error. **BN_hex2bn()** and **BN_dec2bn()** return
the number of characters used in parsing, or 0 on error, in which case no
new **BIGNUM** will be created.

**BN_print_fp()** and **BN_print()** return 1 on success, 0
on write errors.

**BN_bn2mpi()** returns the length of the representation.
**BN_mpi2bn()** returns the **BIGNUM**, and NULL on error.

The error codes can be obtained by ERR_get_error(3).

# SEE ALSO¶

ERR_get_error(3), BN_zero(3), ASN1_INTEGER_to_BN(3), BN_num_bytes(3)

# COPYRIGHT¶

Copyright 2000-2020 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the OpenSSL license (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>.

2022-06-24 | 1.1.1n |