Updated: 2021-03-26

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#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);

**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.

**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).

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>.