## table of contents

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

# NAME¶

BN_bn2binpad, BN_bn2bin, BN_bin2bn, BN_bn2lebinpad, BN_lebin2bn, BN_bn2nativepad, BN_native2bn, 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); int BN_bn2nativepad(const BIGNUM *a, unsigned char *to, int tolen); BIGNUM *BN_native2bn(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_bn2nativepad()** and **BN_native2bn()** are identical
to **BN_bn2binpad()** and **BN_bin2bn()** except the buffer is in
native format, i.e. most significant byte first on big-endian platforms, and
least significant byte first on little-endian platforms.

**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()**, **BN_bn2lebinpad()**, and
**BN_bn2nativepad()** return the number of bytes written or -1 if the
supplied buffer is too small.

**BN_bn2hex()** and **BN_bn2dec()** return a NUL-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 2000-2021 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>.

2022-08-14 | 3.0.5 |