Section: OpenSSL (3)
Updated: 2021-03-26
Page Index


BN_bn2binpad, BN_bn2bin, BN_bin2bn, BN_bn2lebinpad, BN_lebin2bn, BN_bn2hex, BN_bn2dec, BN_hex2bn, BN_dec2bn, BN_print, BN_print_fp, BN_bn2mpi, BN_mpi2bn - format conversions  


 #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_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_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 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 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_bn2bin() returns the length of the big-endian number placed at to. BN_bin2bn() returns the BIGNUM, NULL on error.

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).  


ERR_get_error(3), BN_zero(3), ASN1_INTEGER_to_BN(3), BN_num_bytes(3)  


Copyright 2000-2020 The OpenSSL Project Authors. All Rights Reserved.

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 <>.