## NAME

`BN_bn2bin`

,
`BN_bn2binpad`

, `BN_bin2bn`

,
`BN_bn2lebinpad`

, `BN_lebin2bn`

,
`BN_bn2hex`

, `BN_bn2dec`

,
`BN_hex2bn`

, `BN_dec2bn`

,
`BN_asc2bn`

, `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 **ap`,
`const char *str`);

`int`

`BN_dec2bn`

(`BIGNUM **ap`,
`const char *str`);

`int`

`BN_asc2bn`

(`BIGNUM **ap`,
`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
*`to` 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 minus sign. The string must be freed later using
free(3).

`BN_hex2bn`

()
interprets `str` as a hexadecimal number. The string may
start with a minus sign (‘-’). Conversion stops at the first
byte that is not a hexadecimal digit. The number is converted to a
`BIGNUM` and stored in **`ap`. If
*`ap` is `NULL`

, a new
`BIGNUM` is created. If `ap` is
`NULL`

, it only computes the number's length in
hexadecimal digits, also counting the leading minus sign if there is one. A
"negative zero" is converted to zero.
`BN_dec2bn`

()
is the same using the decimal system.
`BN_asc2bn`

()
infers the number base from an optional prefix. If `str`
starts with "0x" or "0X", it calls
`BN_hex2bn`

(), otherwise
`BN_dec2bn`

(). If the number is negative, the minus
sign can be given before or after the prefix.

`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
`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 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_bn2binpad`

() and
`BN_bn2lebinpad`

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

`BN_bin2bn`

() and
`BN_lebin2bn`

() return 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, also counting the leading minus sign if there
is one, or 0 on error, in which case no new `BIGNUM` is
created. `BN_asc2bn`

() returns 1 on success or 0 on
error, in which case no new `BIGNUM` is 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`, or `NULL`

on error.

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

## SEE ALSO

ASN1_bn_print(3), ASN1_INTEGER_to_BN(3), BN_new(3), BN_num_bytes(3), BN_zero(3)

## HISTORY

`BN_bn2bin`

(),
`BN_bin2bn`

(), and `BN_print`

()
first appeared in SSLeay 0.5.1. `BN_print_fp`

() first
appeared in SSLeay 0.6.0. `BN_bn2hex`

(),
`BN_bn2dec`

(), `BN_hex2bn`

(),
`BN_dec2bn`

(), `BN_bn2mpi`

(),
and `BN_mpi2bn`

() first appeared in SSLeay 0.9.0. All
these functions have been available since OpenBSD
2.4.

`BN_asc2bin`

() first appeared in OpenSSL
1.0.0 and has been available since OpenBSD 4.9.

`BN_bn2binpad`

(),
`BN_bn2lebinpad`

(), and
`BN_lebin2bn`

() first appeared in OpenSSL 1.1.0 and
have been available since OpenBSD 7.0.