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 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_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_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.