# 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 minus sign. The string must be freed later using free(3).

**BN_hex2bn**() converts the string

*str*containing a hexadecimal number 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 number's length in hexadecimal digits. If the string starts with a minus sign, 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 minus sign for negative numbers, to the BIO or FILE

*fp*.

**BN_bn2mpi**() and

**BN_mpi2bn**() convert BIGNUMs 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 a NUL 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, or NULL on error.

**BN_bn2hex**() and

**BN_bn2dec**() return a NUL-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, or NULL on error.

# HISTORY

**BN_bn2bin**(),

**BN_bin2bn**(),

**BN_print_fp**(), and

**BN_print**() are available in all versions of SSLeay and OpenSSL.

**BN_bn2hex**(),

**BN_bn2dec**(),

**BN_hex2bn**(),

**BN_dec2bn**(),

**BN_bn2mpi**(), and

**BN_mpi2bn**() were added in SSLeay 0.9.0.