- NAME
- SYNOPSIS
- DESCRIPTION
- RETURN VALUES
- SEE ALSO
- HISTORY

# 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 '-'. The string must be freed later using OPENSSL_free().

`BN_hex2bn()` converts the string str containing a hexadecimal number to a BIGNUM and stores it in **bn. If *bn is NULL, a new BIGNUM is created. If bn is NULL, it only computes the number's length in hexadecimal digits. If the string starts with '-', the number is negative. 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.

# RETURN VALUES

`BN_bn2bin()` returns the length of the big-endian number placed at to. `BN_bin2bn()` returns the BIGNUM, NULL on error.

`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.

# SEE ALSO

bn, ERR_get_error, BN_zero, ASN1_INTEGER_to_BN, BN_num_bytes

# 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.