=pod

=head1 NAME

SSL_CONF_cmd - send configuration command

=head1 SYNOPSIS

 #include <openssl/ssl.h>

 int SSL_CONF_cmd(SSL_CONF_CTX *cctx, const char *cmd, const char *value);

=head1 DESCRIPTION

The function SSL_CONF_cmd() performs configuration operation B<cmd> with
optional parameter B<value> on B<ctx>. Its purpose is to simplify application
configuration of B<SSL_CTX> or B<SSL> structures by providing a common
framework for command line options or configuration files.

=head1 SUPPORTED COMMAND LINE COMMANDS

Currently supported B<cmd> names for command lines (i.e. when the
flag B<SSL_CONF_CMDLINE> is set) are listed below. Note: all B<cmd> names
and are case sensitive. Unless otherwise stated commands can be used by
both clients and servers and the B<value> parameter is not used. The default
prefix for command line commands is B<-> and that is reflected below.

=over 4

=item B<-sigalgs>

This sets the supported signature algorithms for TLS v1.2. For clients this
value is used directly for the supported signature algorithms extension. For
servers it is used to determine which signature algorithms to support.

The B<value> argument should be a colon separated list of signature algorithms
in order of decreasing preference of the form B<algorithm+hash>. B<algorithm>
is one of B<RSA>, B<DSA> or B<ECDSA> and B<hash> is a supported algorithm
OID short name such as B<SHA1>, B<SHA224>, B<SHA256>, B<SHA384> of B<SHA512>.
Note: algorithm and hash names are case sensitive.

If this option is not set then all signature algorithms supported by the
OpenSSL library are permissible.

=item B<-client_sigalgs>

This sets the supported signature algorithms associated with client
authentication for TLS v1.2. For servers the value is used in the supported
signature algorithms field of a certificate request. For clients it is
used to determine which signature algorithm to with the client certificate.
If a server does not request a certificate this option has no effect.

The syntax of B<value> is identical to B<-sigalgs>. If not set then
the value set for B<-sigalgs> will be used instead.

=item B<-curves>

This sets the supported elliptic curves. For clients the curves are
sent using the supported curves extension. For servers it is used
to determine which curve to use. This setting affects curves used for both
signatures and key exchange, if applicable.

The B<value> argument is a colon separated list of curves. The curve can be
either the B<NIST> name (e.g. B<P-256>) or an OpenSSL OID name (e.g
B<prime256v1>). Curve names are case sensitive.

=item B<-named_curve>

This sets the temporary curve used for ephemeral ECDH modes. Only used by 
servers

The B<value> argument is a curve name or the special value B<auto> which
picks an appropriate curve based on client and server preferences. The curve
can be either the B<NIST> name (e.g. B<P-256>) or an OpenSSL OID name
(e.g B<prime256v1>). Curve names are case sensitive.

=item B<-cipher>

Sets the cipher suite list to B<value>. Note: syntax checking of B<value> is
currently not performed unless a B<SSL> or B<SSL_CTX> structure is 
associated with B<cctx>.

=item B<-no_ssl2>, B<-no_ssl3>, B<-no_tls1>, B<-no_tls1_1>, B<-no_tls1_2>

Disables protocol support for SSLv2, SSLv3, TLS 1.0, TLS 1.1 or TLS 1.2 
by setting the corresponding options B<SSL_OP_NO_SSL2>, B<SSL_OP_NO_SSL3>,
B<SSL_OP_NO_TLS1>, B<SSL_OP_NO_TLS1_1> and B<SSL_OP_NO_TLS1_2> respectively.

=item B<-bugs>

Various bug workarounds are set, same as setting B<SSL_OP_ALL>.

=item B<-no_comp>

Disables support for SSL/TLS compression, same as setting B<SSL_OP_NO_COMPRESS>.

=item B<-no_ticket>

Disables support for session tickets, same as setting B<SSL_OP_NO_TICKET>.

=item B<-serverpref>

Use server and not client preference order when determining which cipher suite,
signature algorithm or elliptic curve to use for an incoming connection.
Equivalent to B<SSL_OP_CIPHER_SERVER_PREFERENCE>. Only used by servers.

=item B<-legacyrenegotiation>

permits the use of unsafe legacy renegotiation. Equivalent to setting
B<SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION>.

=item B<-legacy_server_connect>, B<-no_legacy_server_connect>

permits or prohibits the use of unsafe legacy renegotiation for OpenSSL
clients only. Equivalent to setting or clearing B<SSL_OP_LEGACY_SERVER_CONNECT>.
Set by default.

=item B<-strict>

enables strict mode protocol handling. Equivalent to setting
B<SSL_CERT_FLAG_TLS_STRICT>.

=item B<-debug_broken_protocol>

disables various checks and permits several kinds of broken protocol behaviour
for testing purposes: it should B<NEVER> be used in anything other than a test
environment. Only supported if OpenSSL is configured with
B<-DOPENSSL_SSL_DEBUG_BROKEN_PROTOCOL>.

=back

=head1 SUPPORTED CONFIGURATION FILE COMMANDS

Currently supported B<cmd> names for configuration files (i.e. when the
flag B<SSL_CONF_FLAG_FILE> is set) are listed below. All configuration file
B<cmd> names and are case insensitive so B<signaturealgorithms> is recognised
as well as B<SignatureAlgorithms>. Unless otherwise stated the B<value> names
are also case insensitive.

Note: the command prefix (if set) alters the recognised B<cmd> values.

=over 4

=item B<CipherString>

Sets the cipher suite list to B<value>. Note: syntax checking of B<value> is
currently not performed unless an B<SSL> or B<SSL_CTX> structure is 
associated with B<cctx>.

=item B<SignatureAlgorithms>

This sets the supported signature algorithms for TLS v1.2. For clients this
value is used directly for the supported signature algorithms extension. For
servers it is used to determine which signature algorithms to support.

The B<value> argument should be a colon separated list of signature algorithms
in order of decreasing preference of the form B<algorithm+hash>. B<algorithm>
is one of B<RSA>, B<DSA> or B<ECDSA> and B<hash> is a supported algorithm
OID short name such as B<SHA1>, B<SHA224>, B<SHA256>, B<SHA384> of B<SHA512>.
Note: algorithm and hash names are case sensitive.

If this option is not set then all signature algorithms supported by the
OpenSSL library are permissible.

=item B<ClientSignatureAlgorithms>

This sets the supported signature algorithms associated with client
authentication for TLS v1.2. For servers the value is used in the supported
signature algorithms field of a certificate request. For clients it is
used to determine which signature algorithm to with the client certificate.

The syntax of B<value> is identical to B<SignatureAlgorithms>. If not set then
the value set for B<SignatureAlgorithms> will be used instead.

=item B<Curves>

This sets the supported elliptic curves. For clients the curves are
sent using the supported curves extension. For servers it is used
to determine which curve to use. This setting affects curves used for both
signatures and key exchange, if applicable.

The B<value> argument is a colon separated list of curves. The curve can be
either the B<NIST> name (e.g. B<P-256>) or an OpenSSL OID name (e.g
B<prime256v1>). Curve names are case sensitive.

=item B<ECDHParameters>

This sets the temporary curve used for ephemeral ECDH modes. Only used by 
servers

The B<value> argument is a curve name or the special value B<Automatic> which
picks an appropriate curve based on client and server preferences. The curve
can be either the B<NIST> name (e.g. B<P-256>) or an OpenSSL OID name
(e.g B<prime256v1>). Curve names are case sensitive.

=item B<Protocol>

The supported versions of the SSL or TLS protocol.

The B<value> argument is a comma separated list of supported protocols to
enable or disable. If an protocol is preceded by B<-> that version is disabled.
All versions are enabled by default, though applications may choose to
explicitly disable some. Currently supported protocol values are B<SSLv2>,
B<SSLv3>, B<TLSv1>, B<TLSv1.1> and B<TLSv1.2>. The special value B<ALL> refers
to all supported versions.

=item B<Options>

The B<value> argument is a comma separated list of various flags to set.
If a flag string is preceded B<-> it is disabled. See the
B<SSL_CTX_set_options> function for more details of individual options.

Each option is listed below. Where an operation is enabled by default
the B<-flag> syntax is needed to disable it.

B<SessionTicket>: session ticket support, enabled by default. Inverse of
B<SSL_OP_NO_TICKET>: that is B<-SessionTicket> is the same as setting
B<SSL_OP_NO_TICKET>.

B<Compression>: SSL/TLS compression support, enabled by default. Inverse
of B<SSL_OP_NO_COMPRESSION>.

B<EmptyFragments>: use empty fragments as a countermeasure against a
SSL 3.0/TLS 1.0 protocol vulnerability affecting CBC ciphers. It
is set by default. Inverse of B<SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS>.

B<Bugs>: enable various bug workarounds. Same as B<SSL_OP_ALL>.

B<DHSingle>: enable single use DH keys, set by default. Inverse of
B<SSL_OP_DH_SINGLE>. Only used by servers.

B<ECDHSingle> enable single use ECDH keys, set by default. Inverse of
B<SSL_OP_ECDH_SINGLE>. Only used by servers.

B<ServerPreference> use server and not client preference order when
determining which cipher suite, signature algorithm or elliptic curve
to use for an incoming connection.  Equivalent to
B<SSL_OP_CIPHER_SERVER_PREFERENCE>. Only used by servers.

B<UnsafeLegacyRenegotiation> permits the use of unsafe legacy renegotiation.
Equivalent to B<SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION>.

B<UnsafeLegacyServerConnect> permits the use of unsafe legacy renegotiation
for OpenSSL clients only. Equivalent to B<SSL_OP_LEGACY_SERVER_CONNECT>.
Set by default.

=back

=head1 NOTES

The order of operations is significant. This can be used to set either defaults
or values which cannot be overridden. For example if an application calls:

 SSL_CONF_cmd(ctx, "Protocol", "-SSLv2");
 SSL_CONF_cmd(ctx, userparam, uservalue);

it will disable SSLv2 support by default but the user can override it. If 
however the call sequence is:

 SSL_CONF_cmd(ctx, userparam, uservalue);
 SSL_CONF_cmd(ctx, "Protocol", "-SSLv2");

SSLv2 is B<always> disabled and attempt to override this by the user are
ignored.

By checking the return code of SSL_CTX_cmd() it is possible to query if a
given B<cmd> is recognised, this is useful is SSL_CTX_cmd() values are
mixed with additional application specific operations.

For example an application might call SSL_CTX_cmd() and if it returns
-2 (unrecognised command) continue with processing of application specific
commands.

Applications can also use SSL_CTX_cmd() to process command lines though the
utility function SSL_CTX_cmd_argv() is normally used instead. One way
to do this is to set the prefix to an appropriate value using
SSL_CONF_CTX_set1_prefix(), pass the current argument to B<cmd> and the
following argument to B<value> (which may be NULL).

In this case if the return value is positive then it is used to skip that
number of arguments as they have been processed by SSL_CTX_cmd(). If -2 is
returned then B<cmd> is not recognised and application specific arguments
can be checked instead. If -3 is returned a required argument is missing
and an error is indicated. If 0 is returned some other error occurred and
this can be reported back to the user.

=head1 EXAMPLES

Set supported signature algorithms:

 SSL_CONF_cmd(ctx, "SignatureAlgorithms", "ECDSA+SHA256:RSA+SHA256:DSA+SHA256");

Enable all protocols except SSLv3 and SSLv2:

 SSL_CONF_cmd(ctx, "Protocol", "ALL,-SSLv3,-SSLv2");

Only enable TLSv1.2:

 SSL_CONF_cmd(ctx, "Protocol", "-ALL,TLSv1.2");

Disable TLS session tickets:

 SSL_CONF_cmd(ctx, "Options", "-SessionTicket");

Set supported curves to P-256, P-384:

 SSL_CONF_cmd(ctx, "Curves", "P-256:P-384");

Set automatic support for any elliptic curve for key exchange:

 SSL_CONF_cmd(ctx, "ECDHParameters", "Automatic");

=head1 RETURN VALUES

SSL_CONF_cmd() returns 1 if the value of B<cmd> is recognised and B<value> is
B<NOT> used and 2 if both B<cmd> and B<value> are used. In other words it
returns the number of arguments processed. This is useful when processing
command lines.

A return value of -2 means B<cmd> is not recognised.

A return value of -3 means B<cmd> is recognised and the command requires a
value but B<value> is NULL.

A return code of 0 indicates that both B<cmd> and B<value> are valid but an
error occurred attempting to perform the operation: for example due to an
error in the syntax of B<value> in this case the error queue may provide
additional information.

=head1 SEE ALSO

L<SSL_CONF_CTX_new(3)|SSL_CONF_CTX_new(3)>,
L<SSL_CONF_CTX_set_flags(3)|SSL_CONF_CTX_set_flags(3)>,
L<SSL_CONF_CTX_set1_prefix(3)|SSL_CONF_CTX_set1_prefix(3)>,
L<SSL_CONF_CTX_set_ssl_ctx(3)|SSL_CONF_CTX_set_ssl_ctx(3)>,
L<SSL_CONF_cmd_argv(3)|SSL_CONF_cmd_argv(3)>

=head1 HISTORY

SSL_CONF_cmd() was first added to OpenSSL 1.0.2

=cut