=head1 NAME
-EVP_PKEY_derive_init, EVP_PKEY_derive_set_peer, EVP_PKEY_derive - derive public key algorithm shared secret
+EVP_PKEY_derive_init, EVP_PKEY_derive_init_ex, EVP_PKEY_derive_set_peer,
+EVP_PKEY_derive - derive public key algorithm shared secret
=head1 SYNOPSIS
#include <openssl/evp.h>
+ int EVP_PKEY_derive_init_ex(EVP_PKEY_CTX *ctx, EVP_KEYEXCH *exchange);
int EVP_PKEY_derive_init(EVP_PKEY_CTX *ctx);
int EVP_PKEY_derive_set_peer(EVP_PKEY_CTX *ctx, EVP_PKEY *peer);
int EVP_PKEY_derive(EVP_PKEY_CTX *ctx, unsigned char *key, size_t *keylen);
=head1 DESCRIPTION
-The EVP_PKEY_derive_init() function initializes a public key algorithm
-context using key B<pkey> for shared secret derivation.
+The EVP_PKEY_derive_init_ex() function initializes a public key algorithm
+context for shared secret derivation using the key exchange algorithm
+B<exchange>.
+The key exchange algorithm B<exchange> should be fetched using a call to
+L<EVP_KEYEXCH_fetch(3)>.
+The EVP_PKEY object associated with B<ctx> must be compatible with that
+algorithm.
+B<exchange> may be NULL in which case the EVP_KEYEXCH algorithm is fetched
+implicitly based on the type of EVP_PKEY associated with B<ctx>.
+See L<provider(7)/Implicit fetch> for more information about implict fetches.
+
+The EVP_PKEY_derive_init() function is the same as EVP_PKEY_derive_init_ex()
+except that the EVP_KEYEXCH algorithm is always implicitly fetched.
The EVP_PKEY_derive_set_peer() function sets the peer key: this will normally
be a public key.
=head1 NOTES
-After the call to EVP_PKEY_derive_init() algorithm specific control
-operations can be performed to set any appropriate parameters for the
-operation.
+After the call to EVP_PKEY_derive_init() or EVP_PKEY_derive_init_ex() algorithm
+specific control operations can be performed to set any appropriate parameters
+for the operation.
The function EVP_PKEY_derive() can be called more than once on the same
context if several operations are performed using the same parameters.
=head1 RETURN VALUES
-EVP_PKEY_derive_init() and EVP_PKEY_derive() return 1 for success and 0
-or a negative value for failure. In particular a return value of -2
-indicates the operation is not supported by the public key algorithm.
+EVP_PKEY_derive_init_ex(), EVP_PKEY_derive_init() and EVP_PKEY_derive() return 1
+for success and 0 or a negative value for failure.
+In particular a return value of -2 indicates the operation is not supported by
+the public key algorithm.
-=head1 EXAMPLE
+=head1 EXAMPLES
Derive shared secret (for example DH or EC keys):
#include <openssl/rsa.h>
EVP_PKEY_CTX *ctx;
+ ENGINE *eng;
unsigned char *skey;
size_t skeylen;
EVP_PKEY *pkey, *peerkey;
- /* NB: assumes pkey, peerkey have been already set up */
+ /* NB: assumes pkey, eng, peerkey have been already set up */
- ctx = EVP_PKEY_CTX_new(pkey);
+ ctx = EVP_PKEY_CTX_new(pkey, eng);
if (!ctx)
- /* Error occurred */
+ /* Error occurred */
if (EVP_PKEY_derive_init(ctx) <= 0)
- /* Error */
+ /* Error */
if (EVP_PKEY_derive_set_peer(ctx, peerkey) <= 0)
- /* Error */
+ /* Error */
/* Determine buffer length */
if (EVP_PKEY_derive(ctx, NULL, &skeylen) <= 0)
- /* Error */
+ /* Error */
skey = OPENSSL_malloc(skeylen);
if (!skey)
- /* malloc failure */
+ /* malloc failure */
if (EVP_PKEY_derive(ctx, skey, &skeylen) <= 0)
- /* Error */
+ /* Error */
/* Shared secret is skey bytes written to buffer skey */
L<EVP_PKEY_sign(3)>,
L<EVP_PKEY_verify(3)>,
L<EVP_PKEY_verify_recover(3)>,
+L<EVP_KEYEXCH_fetch(3)>
=head1 HISTORY
-These functions were first added to OpenSSL 1.0.0.
+These functions were added in OpenSSL 1.0.0. The EVP_PKEY_derive_init_ex()
+function was added in OpenSSL 3.0.
=head1 COPYRIGHT
-Copyright 2006-2016 The OpenSSL Project Authors. All Rights Reserved.
+Copyright 2006-2018 The OpenSSL Project Authors. All Rights Reserved.
-Licensed under the OpenSSL license (the "License"). You may not use
+Licensed under the Apache License 2.0 (the "License"). You may not use
this file except in compliance with the License. You can obtain a copy
in the file LICENSE in the source distribution or at
L<https://www.openssl.org/source/license.html>.