# BN_bn2bin

## Name

BN_bn2bin, BN_bin2bn, 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); BIGNUM *BN_bin2bn(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_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_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() converts the string **str**
containing a hexadecimal number to a **BIGNUM** and stores it in ****bn**. If ***bn** is
NULL, a new **BIGNUM** is created. If
**bn** is NULL, it only computes the
number's length in hexadecimal digits. If the string starts with '-',
the number is negative. 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_bn2hex() and BN_bn2dec() return a null-terminated string, or NULL on error. BN_hex2bn() and BN_dec2bn() return the number's length in hexadecimal or decimal digits, and 0 on error.

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).