mirror of
https://github.com/openssl/openssl.git
synced 2024-12-15 06:01:37 +08:00
123 lines
5.6 KiB
Plaintext
123 lines
5.6 KiB
Plaintext
=pod
|
|
|
|
=head1 NAME
|
|
|
|
SSL_CTX_set_dh_auto, SSL_set_dh_auto, SSL_CTX_set0_tmp_dh_pkey,
|
|
SSL_set0_tmp_dh_pkey, SSL_CTX_set_tmp_dh_callback, SSL_CTX_set_tmp_dh,
|
|
SSL_set_tmp_dh_callback, SSL_set_tmp_dh
|
|
- handle DH keys for ephemeral key exchange
|
|
|
|
=head1 SYNOPSIS
|
|
|
|
#include <openssl/ssl.h>
|
|
|
|
long SSL_CTX_set_dh_auto(SSL_CTX *ctx, int onoff);
|
|
long SSL_set_dh_auto(SSL *s, int onoff);
|
|
int SSL_CTX_set0_tmp_dh_pkey(SSL_CTX *ctx, EVP_PKEY *dhpkey);
|
|
int SSL_set0_tmp_dh_pkey(SSL *s, EVP_PKEY *dhpkey);
|
|
|
|
The following functions have been deprecated since OpenSSL 3.0, and can be
|
|
hidden entirely by defining B<OPENSSL_API_COMPAT> with a suitable version value,
|
|
see L<openssl_user_macros(7)>:
|
|
|
|
void SSL_CTX_set_tmp_dh_callback(SSL_CTX *ctx,
|
|
DH *(*tmp_dh_callback)(SSL *ssl, int is_export,
|
|
int keylength));
|
|
long SSL_CTX_set_tmp_dh(SSL_CTX *ctx, DH *dh);
|
|
|
|
void SSL_set_tmp_dh_callback(SSL *ctx,
|
|
DH *(*tmp_dh_callback)(SSL *ssl, int is_export,
|
|
int keylength));
|
|
long SSL_set_tmp_dh(SSL *ssl, DH *dh);
|
|
|
|
=head1 DESCRIPTION
|
|
|
|
The functions described on this page are relevant for servers only.
|
|
|
|
Some ciphersuites may use ephemeral Diffie-Hellman (DH) key exchange. In these
|
|
cases, the session data is negotiated using the ephemeral/temporary DH key and
|
|
the key supplied and certified by the certificate chain is only used for
|
|
signing. Anonymous ciphers (without a permanent server key) also use ephemeral
|
|
DH keys.
|
|
|
|
Using ephemeral DH key exchange yields forward secrecy as the connection
|
|
can only be decrypted when the DH key is known. By generating a temporary
|
|
DH key inside the server application that is lost when the application
|
|
is left, it becomes impossible for an attacker to decrypt past sessions,
|
|
even if they get hold of the normal (certified) key, as this key was
|
|
only used for signing.
|
|
|
|
In order to perform a DH key exchange the server must use a DH group
|
|
(DH parameters) and generate a DH key. The server will always generate
|
|
a new DH key during the negotiation.
|
|
|
|
As generating DH parameters is extremely time consuming, an application
|
|
should not generate the parameters on the fly. DH parameters can be reused, as
|
|
the actual key is newly generated during the negotiation.
|
|
|
|
Typically applications should use well know DH parameters that have built-in
|
|
support in OpenSSL. The macros SSL_CTX_set_dh_auto() and SSL_set_dh_auto()
|
|
configure OpenSSL to use the default built-in DH parameters for the B<SSL_CTX>
|
|
and B<SSL> objects respectively. Passing a value of 1 in the I<onoff> parameter
|
|
switches the feature on, and passing a value of 0 switches it off. The default
|
|
setting is off.
|
|
|
|
If "auto" DH parameters are switched on then the parameters will be selected to
|
|
be consistent with the size of the key associated with the server's certificate.
|
|
If there is no certificate (e.g. for PSK ciphersuites), then it it will be
|
|
consistent with the size of the negotiated symmetric cipher key.
|
|
|
|
Applications may supply their own DH parameters instead of using the built-in
|
|
values. This approach is discouraged and applications should in preference use
|
|
the built-in parameter support described above. Applications wishing to supply
|
|
their own DH parameters should call SSL_CTX_set0_tmp_dh_pkey() or
|
|
SSL_set0_tmp_dh_pkey() to supply the parameters for the B<SSL_CTX> or B<SSL>
|
|
respectively. The parameters should be supplied in the I<dhpkey> argument as
|
|
an B<EVP_PKEY> containing DH parameters. Ownership of the I<dhpkey> value is
|
|
passed to the B<SSL_CTX> or B<SSL> object as a result of this call, and so the
|
|
caller should not free it if the function call is successful.
|
|
|
|
The deprecated macros SSL_CTX_set_tmp_dh() and SSL_set_tmp_dh() do the same
|
|
thing as SSL_CTX_set0_tmp_dh_pkey() and SSL_set0_tmp_dh_pkey() except that the
|
|
DH parameters are supplied in a B<DH> object instead in the I<dh> argument, and
|
|
ownership of the B<DH> object is retained by the application. Applications
|
|
should use "auto" parameters instead, or call SSL_CTX_set0_tmp_dh_pkey() or
|
|
SSL_set0_tmp_dh_pkey() as appropriate.
|
|
|
|
An application may instead specify the DH parameters via a callback function
|
|
using the functions SSL_CTX_set_tmp_dh_callback() or SSL_set_tmp_dh_callback()
|
|
to set the callback for the B<SSL_CTX> or B<SSL> object respectively. These
|
|
functions are deprecated. Applications should instead use "auto" parameters, or
|
|
specify the parameters via SSL_CTX_set0_tmp_dh_pkey() or SSL_set0_tmp_dh_pkey()
|
|
as appropriate.
|
|
|
|
The callback will be invoked during a connection when DH parameters are
|
|
required. The B<SSL> object for the current connection is supplied as an
|
|
argument. Previous versions of OpenSSL used the B<is_export> and B<keylength>
|
|
arguments to control parameter generation for export and non-export
|
|
cipher suites. Modern OpenSSL does not support export ciphersuites and so these
|
|
arguments are unused and can be ignored by the callback. The callback should
|
|
return the parameters to be used in a DH object. Ownership of the DH object is
|
|
retained by the application and should later be freed.
|
|
|
|
=head1 RETURN VALUES
|
|
|
|
All of these functions/macros return 1 for success or 0 on error.
|
|
|
|
=head1 SEE ALSO
|
|
|
|
L<ssl(7)>, L<SSL_CTX_set_cipher_list(3)>,
|
|
L<SSL_CTX_set_options(3)>,
|
|
L<openssl-ciphers(1)>, L<openssl-dhparam(1)>
|
|
|
|
=head1 COPYRIGHT
|
|
|
|
Copyright 2001-2022 The OpenSSL Project Authors. All Rights Reserved.
|
|
|
|
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>.
|
|
|
|
=cut
|