.\"	$OpenBSD: EVP_PKEY_CTX_new.3,v 1.7 2018/03/23 04:34:23 schwarze Exp $
.\"	OpenSSL 99d63d46 Oct 26 13:56:48 2016 -0400
.\"
.\" This file was written by Dr. Stephen Henson <steve@openssl.org>.
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.Dd $Mdocdate: March 23 2018 $
.Dt EVP_PKEY_CTX_NEW 3
.Os
.Sh NAME
.Nm EVP_PKEY_CTX_new ,
.Nm EVP_PKEY_CTX_new_id ,
.Nm EVP_PKEY_CTX_dup ,
.Nm EVP_PKEY_CTX_free
.Nd public key algorithm context functions
.Sh SYNOPSIS
.In openssl/evp.h
.Ft EVP_PKEY_CTX *
.Fo EVP_PKEY_CTX_new
.Fa "EVP_PKEY *pkey"
.Fa "ENGINE *e"
.Fc
.Ft EVP_PKEY_CTX *
.Fo EVP_PKEY_CTX_new_id
.Fa "int id"
.Fa "ENGINE *e"
.Fc
.Ft EVP_PKEY_CTX *
.Fo EVP_PKEY_CTX_dup
.Fa "EVP_PKEY_CTX *ctx"
.Fc
.Ft void
.Fo EVP_PKEY_CTX_free
.Fa "EVP_PKEY_CTX *ctx"
.Fc
.Sh DESCRIPTION
The
.Fn EVP_PKEY_CTX_new
function allocates a public key algorithm context using the algorithm
specified in
.Fa pkey
and the
.Vt ENGINE
.Fa e .
.Pp
The
.Fn EVP_PKEY_CTX_new_id
function allocates a public key algorithm context using the algorithm
specified by
.Fa id
and
.Vt ENGINE
.Fa e .
It is normally used when no
.Vt EVP_PKEY
structure is associated with the operations, for example during
parameter generation of key generation for some algorithms.
.Pp
.Fn EVP_PKEY_CTX_dup
duplicates the context
.Fa ctx .
.Pp
.Fn EVP_PKEY_CTX_free
frees up the context
.Fa ctx .
If
.Fa ctx
is a
.Dv NULL
pointer, no action occurs.
.Sh RETURN VALUES
.Fn EVP_PKEY_CTX_new ,
.Fn EVP_PKEY_CTX_new_id ,
and
.Fn EVP_PKEY_CTX_dup
return either the newly allocated
.Vt EVP_PKEY_CTX
structure or
.Dv NULL
if an error occurred.
.Sh SEE ALSO
.Xr EVP_PKEY_meth_set_init 3 ,
.Xr EVP_PKEY_new 3 ,
.Xr X25519 3
.Sh HISTORY
These functions first appeared in OpenSSL 1.0.0
and have been available since
.Ox 4.9 .
.Sh CAVEATS
The
.Vt EVP_PKEY_CTX
structure is an opaque public key algorithm context used by the OpenSSL
high level public key API.
Contexts
.Sy MUST NOT
be shared between threads.
It is not permissible to use the same context simultaneously in two
threads.