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.IX Title "BN_bn2bin 3"
.TH BN_bn2bin 3 2019-12-20 1.0.2u OpenSSL
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
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.nh
.SH NAME
BN_bn2bin, BN_bin2bn, BN_bn2hex, BN_bn2dec, BN_hex2bn, BN_dec2bn,
BN_print, BN_print_fp, BN_bn2mpi, BN_mpi2bn \- format conversions
.SH SYNOPSIS
.IX Header "SYNOPSIS"
.Vb 1
\& #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);
.Ve
.SH DESCRIPTION
.IX Header "DESCRIPTION"
\&\fBBN_bn2bin()\fR converts the absolute value of \fBa\fR into big-endian form
and stores it at \fBto\fR. \fBto\fR must point to BN_num_bytes(\fBa\fR) bytes of
memory.
.PP
\&\fBBN_bin2bn()\fR converts the positive integer in big-endian form of length
\&\fBlen\fR at \fBs\fR into a \fBBIGNUM\fR and places it in \fBret\fR. If \fBret\fR is
NULL, a new \fBBIGNUM\fR is created.
.PP
\&\fBBN_bn2hex()\fR and \fBBN_bn2dec()\fR return printable strings containing the
hexadecimal and decimal encoding of \fBa\fR respectively. For negative
numbers, the string is prefaced with a leading '\-'. The string must be
freed later using \fBOPENSSL_free()\fR.
.PP
\&\fBBN_hex2bn()\fR converts the string \fBstr\fR containing a hexadecimal number
to a \fBBIGNUM\fR and stores it in **\fBa\fR. If *\fBa\fR is NULL, a new
\&\fBBIGNUM\fR is created. If \fBa\fR 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.
\&\fBBN_dec2bn()\fR is the same using the decimal system.
.PP
\&\fBBN_print()\fR and \fBBN_print_fp()\fR write the hexadecimal encoding of \fBa\fR,
with a leading '\-' for negative numbers, to the \fBBIO\fR or \fBFILE\fR
\&\fBfp\fR.
.PP
\&\fBBN_bn2mpi()\fR and \fBBN_mpi2bn()\fR convert \fBBIGNUM\fRs 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).
.PP
\&\fBBN_bn2mpi()\fR stores the representation of \fBa\fR at \fBto\fR, where \fBto\fR
must be large enough to hold the result. The size can be determined by
calling BN_bn2mpi(\fBa\fR, NULL).
.PP
\&\fBBN_mpi2bn()\fR converts the \fBlen\fR bytes long representation at \fBs\fR to
a \fBBIGNUM\fR and stores it at \fBret\fR, or in a newly allocated \fBBIGNUM\fR
if \fBret\fR is NULL.
.SH "RETURN VALUES"
.IX Header "RETURN VALUES"
\&\fBBN_bn2bin()\fR returns the length of the big-endian number placed at \fBto\fR.
\&\fBBN_bin2bn()\fR returns the \fBBIGNUM\fR, NULL on error.
.PP
\&\fBBN_bn2hex()\fR and \fBBN_bn2dec()\fR return a null-terminated string, or NULL
on error. \fBBN_hex2bn()\fR and \fBBN_dec2bn()\fR return the number of characters
used in parsing, or 0 on error, in which
case no new \fBBIGNUM\fR will be created.
.PP
\&\fBBN_print_fp()\fR and \fBBN_print()\fR return 1 on success, 0 on write errors.
.PP
\&\fBBN_bn2mpi()\fR returns the length of the representation. \fBBN_mpi2bn()\fR
returns the \fBBIGNUM\fR, and NULL on error.
.PP
The error codes can be obtained by \fBERR_get_error\fR\|(3).
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fBbn\fR\|(3), \fBERR_get_error\fR\|(3), \fBBN_zero\fR\|(3),
\&\fBASN1_INTEGER_to_BN\fR\|(3),
\&\fBBN_num_bytes\fR\|(3)
.SH HISTORY
.IX Header "HISTORY"
\&\fBBN_bn2bin()\fR, \fBBN_bin2bn()\fR, \fBBN_print_fp()\fR and \fBBN_print()\fR are available
in all versions of SSLeay and OpenSSL.
.PP
\&\fBBN_bn2hex()\fR, \fBBN_bn2dec()\fR, \fBBN_hex2bn()\fR, \fBBN_dec2bn()\fR, \fBBN_bn2mpi()\fR and
\&\fBBN_mpi2bn()\fR were added in SSLeay 0.9.0.