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=head1 NAME

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

=head1 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);

=head1 DESCRIPTION

BN_bn2bin() converts the absolute value of B<a> into big-endian form
and stores it at B<to>. B<to> must point to BN_num_bytes(B<a>) bytes of
memory.

BN_bin2bn() converts the positive integer in big-endian form of length
B<len> at B<s> into a B<BIGNUM> and places it in B<ret>. If B<ret> is
NULL, a new B<BIGNUM> is created.

BN_bn2hex() and BN_bn2dec() return printable strings containing the
hexadecimal and decimal encoding of B<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 B<str> containing a hexadecimal number
to a B<BIGNUM> and stores it in **B<bn>. If *B<bn> is NULL, a new
B<BIGNUM> is created. If B<bn> is NULL, it only computes the number's
length in hexadecimal digits. If the string starts with '-', the
number is negative. BN_dec2bn() is the same using the decimal system.

BN_print() and BN_print_fp() write the hexadecimal encoding of B<a>,
with a leading '-' for negative numbers, to the B<BIO> or B<FILE>
B<fp>.

BN_bn2mpi() and BN_mpi2bn() convert B<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 B<a> at B<to>, where B<to>
must be large enough to hold the result. The size can be determined by
calling BN_bn2mpi(B<a>, NULL).

BN_mpi2bn() converts the B<len> bytes long representation at B<s> to
a B<BIGNUM> and stores it at B<ret>, or in a newly allocated B<BIGNUM>
if B<ret> is NULL.

=head1 RETURN VALUES

BN_bn2bin() returns the length of the big-endian number placed at B<to>.
BN_bin2bn() returns the B<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's length in
hexadecimal or decimal digits, and 0 on error.

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 B<BIGNUM>, and NULL on error.

The error codes can be obtained by L<ERR_get_error(3)|ERR_get_error(3)>.

=head1 SEE ALSO

L<bn(3)|bn(3)>, L<ERR_get_error(3)|ERR_get_error(3)>, L<BN_zero(3)|BN_zero(3)>,
L<ASN1_INTEGER_to_BN(3)|ASN1_INTEGER_to_BN(3)>,
L<BN_num_bytes(3)|BN_num_bytes(3)>

=head1 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.

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