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.\" ========================================================================
.\"
.IX Title "BN_CTX_new 3"
.TH BN_CTX_new 3 "2023-05-07" "3.0.9" "OpenSSL"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.nh
.SH "NAME"
BN_CTX_new_ex, BN_CTX_new, BN_CTX_secure_new_ex, BN_CTX_secure_new, BN_CTX_free
\&\- allocate and free BN_CTX structures
.SH "LIBRARY"
libcrypto, -lcrypto
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\& #include <openssl/bn.h>
\&
\& BN_CTX *BN_CTX_new_ex(OSSL_LIB_CTX *ctx);
\& BN_CTX *BN_CTX_new(void);
\&
\& BN_CTX *BN_CTX_secure_new_ex(OSSL_LIB_CTX *ctx);
\& BN_CTX *BN_CTX_secure_new(void);
\&
\& void BN_CTX_free(BN_CTX *c);
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
A \fB\s-1BN_CTX\s0\fR is a structure that holds \fB\s-1BIGNUM\s0\fR temporary variables used by
library functions. Since dynamic memory allocation to create \fB\s-1BIGNUM\s0\fRs
is rather expensive when used in conjunction with repeated subroutine
calls, the \fB\s-1BN_CTX\s0\fR structure is used.
.PP
\&\fBBN_CTX_new_ex()\fR allocates and initializes a \fB\s-1BN_CTX\s0\fR structure for the given
library context \fBctx\fR. The <ctx> value may be \s-1NULL\s0 in which case the default
library context will be used. \fBBN_CTX_new()\fR is the same as \fBBN_CTX_new_ex()\fR except
that the default library context is always used.
.PP
\&\fBBN_CTX_secure_new_ex()\fR allocates and initializes a \fB\s-1BN_CTX\s0\fR structure
but uses the secure heap (see \fBCRYPTO_secure_malloc\fR\|(3)) to hold the
\&\fB\s-1BIGNUM\s0\fRs for the given library context \fBctx\fR. The <ctx> value may be \s-1NULL\s0 in
which case the default library context will be used. \fBBN_CTX_secure_new()\fR is the
same as \fBBN_CTX_secure_new_ex()\fR except that the default library context is always
used.
.PP
\&\fBBN_CTX_free()\fR frees the components of the \fB\s-1BN_CTX\s0\fR and the structure itself.
Since \fBBN_CTX_start()\fR is required in order to obtain \fB\s-1BIGNUM\s0\fRs from the
\&\fB\s-1BN_CTX\s0\fR, in most cases \fBBN_CTX_end()\fR must be called before the \fB\s-1BN_CTX\s0\fR may
be freed by \fBBN_CTX_free()\fR.  If \fBc\fR is \s-1NULL,\s0 nothing is done.
.PP
A given \fB\s-1BN_CTX\s0\fR must only be used by a single thread of execution.  No
locking is performed, and the internal pool allocator will not properly handle
multiple threads of execution.
.SH "RETURN VALUES"
.IX Header "RETURN VALUES"
\&\fBBN_CTX_new()\fR and \fBBN_CTX_secure_new()\fR return a pointer to the \fB\s-1BN_CTX\s0\fR.
If the allocation fails,
they return \fB\s-1NULL\s0\fR and sets an error code that can be obtained by
\&\fBERR_get_error\fR\|(3).
.PP
\&\fBBN_CTX_free()\fR has no return values.
.SH "REMOVED FUNCTIONALITY"
.IX Header "REMOVED FUNCTIONALITY"
.Vb 1
\& void BN_CTX_init(BN_CTX *c);
.Ve
.PP
\&\fBBN_CTX_init()\fR is no longer available as of OpenSSL 1.1.0. Applications should
replace use of BN_CTX_init with BN_CTX_new instead:
.PP
.Vb 6
\& BN_CTX *ctx;
\& ctx = BN_CTX_new();
\& if (!ctx)
\&     /* error */
\& ...
\& BN_CTX_free(ctx);
.Ve
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fBERR_get_error\fR\|(3), \fBBN_add\fR\|(3),
\&\fBBN_CTX_start\fR\|(3)
.SH "HISTORY"
.IX Header "HISTORY"
\&\fBBN_CTX_init()\fR was removed in OpenSSL 1.1.0.
.SH "COPYRIGHT"
.IX Header "COPYRIGHT"
Copyright 2000\-2020 The OpenSSL Project Authors. All Rights Reserved.
.PP
Licensed under the Apache License 2.0 (the \*(L"License\*(R").  You may not use
this file except in compliance with the License.  You can obtain a copy
in the file \s-1LICENSE\s0 in the source distribution or at
<https://www.openssl.org/source/license.html>.