doc/man3/SSL_CONF_cmd.pod - third_party/openssl - Git at Google

 =pod

 =head1 NAME

 SSL_CONF_cmd_value_type, SSL_CONF_finish,
 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);
  int SSL_CONF_cmd_value_type(SSL_CONF_CTX *cctx, const char *cmd);
  int SSL_CONF_finish(SSL_CONF_CTX *cctx);

 =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.

 SSL_CONF_cmd_value_type() returns the type of value that B<cmd> refers to.

 The function SSL_CONF_finish() must be called after all configuration
 operations have been completed. It is used to finalise any operations
 or to process defaults.

 =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
 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<-cert>

 Attempts to use the file B<value> as the certificate for the appropriate
 context. It currently uses SSL_CTX_use_certificate_chain_file() if an B<SSL_CTX>
 structure is set or SSL_use_certificate_file() with filetype PEM if an B<SSL>
 structure is set. This option is only supported if certificate operations
 are permitted.

 =item B<-key>

 Attempts to use the file B<value> as the private key for the appropriate
 context. This option is only supported if certificate operations
 are permitted. Note: if no B<-key> option is set then a private key is
 not loaded unless the flag B<SSL_CONF_FLAG_REQUIRE_PRIVATE> is set.

 =item B<-dhparam>

 Attempts to use the file B<value> as the set of temporary DH parameters for
 the appropriate context. This option is only supported if certificate
 operations are permitted.

 =item B<-min_protocol>, B<-max_protocol>

 Sets the minimum and maximum supported protocol.
 Currently supported protocol values are B<SSLv3>, B<TLSv1>,
 B<TLSv1.1>, B<TLSv1.2> for TLS and B<DTLSv1>, B<DTLSv1.2> for DTLS,
 and B<None> for no limit.
 If the either bound is not specified then only the other bound applies,
 if specified.
 To restrict the supported protocol versions use these commands rather
 than the deprecated alternative commands below.

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

 Disables protocol support for SSLv3, TLSv1.0, TLSv1.1 or TLSv1.2 by setting the
 corresponding options B<SSL_OP_NO_SSLv3>, B<SSL_OP_NO_TLSv1>, B<SSL_OP_NO_TLSv1_1>
 and B<SSL_OP_NO_TLSv1_2> respectively.
 These options are deprecated, instead use B<-min_protocol> and B<-max_protocol>.

 =item B<-bugs>

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

 =item B<-comp>

 Enables support for SSL/TLS compression, same as clearing
 B<SSL_OP_NO_COMPRESSION>.
 This command was introduced in OpenSSL 1.1.0.
 As of OpenSSL 1.1.0, compression is off by default.

 =item B<-no_comp>

 Disables support for SSL/TLS compression, same as setting
 B<SSL_OP_NO_COMPRESSION>.
 As of OpenSSL 1.1.0, compression is off by default.

 =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<-no_resumption_on_reneg>

 set SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION flag. 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>.

 =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 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<Certificate>

 Attempts to use the file B<value> as the certificate for the appropriate
 context. It currently uses SSL_CTX_use_certificate_chain_file() if an B<SSL_CTX>
 structure is set or SSL_use_certificate_file() with filetype PEM if an B<SSL>
 structure is set. This option is only supported if certificate operations
 are permitted.

 =item B<PrivateKey>

 Attempts to use the file B<value> as the private key for the appropriate
 context. This option is only supported if certificate operations
 are permitted. Note: if no B<PrivateKey> option is set then a private key is
 not loaded unless the B<SSL_CONF_FLAG_REQUIRE_PRIVATE> is set.

 =item B<ChainCAFile>, B<ChainCAPath>, B<VerifyCAFile>, B<VerifyCAPath>

 These options indicate a file or directory used for building certificate
 chains or verifying certificate chains. These options are only supported
 if certificate operations are permitted.

 =item B<ServerInfoFile>

 Attempts to use the file B<value> in the "serverinfo" extension using the
 function SSL_CTX_use_serverinfo_file.

 =item B<DHParameters>

 Attempts to use the file B<value> as the set of temporary DH parameters for
 the appropriate context. This option is only supported if certificate
 operations are permitted.

 =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<MinProtocol>

 This sets the minimum supported SSL, TLS or DTLS version.

 Currently supported protocol values are B<SSLv3>, B<TLSv1>, B<TLSv1.1>,
 B<TLSv1.2>, B<DTLSv1> and B<DTLSv1.2>.
 The value B<None> will disable the limit.

 =item B<MaxProtocol>

 This sets the maximum supported SSL, TLS or DTLS version.

 Currently supported protocol values are B<SSLv3>, B<TLSv1>, B<TLSv1.1>,
 B<TLSv1.2>, B<DTLSv1> and B<DTLSv1.2>.
 The value B<None> will disable the limit.

 =item B<Protocol>

 This can be used to enable or disable certain versions of the SSL,
 TLS or DTLS protocol.

 The B<value> argument is a comma separated list of supported protocols
 to enable or disable.
 If a protocol is preceded by B<-> that version is disabled.

 All protocol versions are enabled by default.
 You need to disable at least one protocol version for this setting have any
 effect.
 Only enabling some protocol versions does not disable the other protocol
 versions.

 Currently supported protocol values are B<SSLv3>, B<TLSv1>, B<TLSv1.1>,
 B<TLSv1.2>, B<DTLSv1> and B<DTLSv1.2>.
 The special value B<ALL> refers to all supported versions.

 This can't enable protocols that are disabled using B<MinProtocol>
 or B<MaxProtocol>, but can disable protocols that are still allowed
 by them.

 The B<Protocol> command is fragile and deprecated; do not use it.
 Use B<MinProtocol> and B<MaxProtocol> instead.
 If you do use B<Protocol>, make sure that the resulting range of enabled
 protocols has no "holes", e.g. if TLS 1.0 and TLS 1.2 are both enabled, make
 sure to also leave TLS 1.1 enabled.

 =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 L<SSL_CTX_set_options(3)> 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<NoResumptionOnRenegotiation> set
 B<SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION> flag. 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.

 =item B<VerifyMode>

 The B<value> argument is a comma separated list of flags to set.

 B<Peer> enables peer verification: for clients only.

 B<Request> requests but does not require a certificate from the client.
 Servers only.

 B<Require> requests and requires a certificate from the client: an error
 occurs if the client does not present a certificate. Servers only.

 B<Once> requests a certificate from a client only on the initial connection:
 not when renegotiating. Servers only.

 =item B<ClientCAFile>, B<ClientCAPath>

 A file or directory of certificates in PEM format whose names are used as the
 set of acceptable names for client CAs. Servers only. This option is only
 supported if certificate operations are permitted.

 =back

 =head1 SUPPORTED COMMAND TYPES

 The function SSL_CONF_cmd_value_type() currently returns one of the following
 types:

 =over 4

 =item B<SSL_CONF_TYPE_UNKNOWN>

 The B<cmd> string is unrecognised, this return value can be use to flag
 syntax errors.

 =item B<SSL_CONF_TYPE_STRING>

 The value is a string without any specific structure.

 =item B<SSL_CONF_TYPE_FILE>

 The value is a file name.

 =item B<SSL_CONF_TYPE_DIR>

 The value is a directory name.

 =item B<SSL_CONF_TYPE_NONE>

 The value string is not used e.g. a command line option which doesn't take an
 argument.

 =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", "-SSLv3");
  SSL_CONF_cmd(ctx, userparam, uservalue);

 it will disable SSLv3 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", "-SSLv3");

 SSLv3 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.

 The function SSL_CONF_cmd_value_type() can be used by applications to
 check for the existence of a command or to perform additional syntax
 checking or translation of the command value. For example if the return
 value is B<SSL_CONF_TYPE_FILE> an application could translate a relative
 pathname to an absolute pathname.

 =head1 EXAMPLES

 Set supported signature algorithms:

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

 There are various ways to select the supported protocols.

 This set the minimum protocol version to TLSv1, and so disables SSLv3.
 This is the recommended way to disable protocols.

  SSL_CONF_cmd(ctx, "MinProtocol", "TLSv1");

 The following also disables SSLv3:

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

 The following will first enable all protocols, and then disable
 SSLv3.
 If no protocol versions were disabled before this has the same effect as
 "-SSLv3", but if some versions were disables this will re-enable them before
 disabling SSLv3.

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

 Only enable TLSv1.2:

  SSL_CONF_cmd(ctx, "MinProtocol", "TLSv1.2");
  SSL_CONF_cmd(ctx, "MaxProtocol", "TLSv1.2");

 This also only enables TLSv1.2:

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

 Disable TLS session tickets:

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

 Enable compression:

  SSL_CONF_cmd(ctx, "Options", "Compression");

 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.

 SSL_CONF_finish() returns 1 for success and 0 for failure.

 =head1 SEE ALSO

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

 =head1 HISTORY

 SSL_CONF_cmd() was first added to OpenSSL 1.0.2

 B<SSL_OP_NO_SSL2> doesn't have effect since 1.1.0, but the macro is retained
 for backwards compatibility.

 B<SSL_CONF_TYPE_NONE> was first added to OpenSSL 1.1.0. In earlier versions of
 OpenSSL passing a command which didn't take an argument would return
 B<SSL_CONF_TYPE_UNKNOWN>.

 B<MinProtocol> and B<MaxProtocol> where added in OpenSSL 1.1.0.

 =head1 COPYRIGHT

 Copyright 2012-2016 The OpenSSL Project Authors. All Rights Reserved.

 Licensed under the OpenSSL license (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
	=pod

	=head1 NAME

	SSL_CONF_cmd_value_type, SSL_CONF_finish,
	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);
	int SSL_CONF_cmd_value_type(SSL_CONF_CTX cctx, const char cmd);
	int SSL_CONF_finish(SSL_CONF_CTX *cctx);

	=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.

	SSL_CONF_cmd_value_type() returns the type of value that B<cmd> refers to.

	The function SSL_CONF_finish() must be called after all configuration
	operations have been completed. It is used to finalise any operations
	or to process defaults.

	=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
	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<-cert>

	Attempts to use the file B<value> as the certificate for the appropriate
	context. It currently uses SSL_CTX_use_certificate_chain_file() if an B<SSL_CTX>
	structure is set or SSL_use_certificate_file() with filetype PEM if an B<SSL>
	structure is set. This option is only supported if certificate operations
	are permitted.

	=item B<-key>

	Attempts to use the file B<value> as the private key for the appropriate
	context. This option is only supported if certificate operations
	are permitted. Note: if no B<-key> option is set then a private key is
	not loaded unless the flag B<SSL_CONF_FLAG_REQUIRE_PRIVATE> is set.

	=item B<-dhparam>

	Attempts to use the file B<value> as the set of temporary DH parameters for
	the appropriate context. This option is only supported if certificate
	operations are permitted.

	=item B<-min_protocol>, B<-max_protocol>

	Sets the minimum and maximum supported protocol.
	Currently supported protocol values are B<SSLv3>, B<TLSv1>,
	B<TLSv1.1>, B<TLSv1.2> for TLS and B<DTLSv1>, B<DTLSv1.2> for DTLS,
	and B<None> for no limit.
	If the either bound is not specified then only the other bound applies,
	if specified.
	To restrict the supported protocol versions use these commands rather
	than the deprecated alternative commands below.

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

	Disables protocol support for SSLv3, TLSv1.0, TLSv1.1 or TLSv1.2 by setting the
	corresponding options B<SSL_OP_NO_SSLv3>, B<SSL_OP_NO_TLSv1>, B<SSL_OP_NO_TLSv1_1>
	and B<SSL_OP_NO_TLSv1_2> respectively.
	These options are deprecated, instead use B<-min_protocol> and B<-max_protocol>.

	=item B<-bugs>

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

	=item B<-comp>

	Enables support for SSL/TLS compression, same as clearing
	B<SSL_OP_NO_COMPRESSION>.
	This command was introduced in OpenSSL 1.1.0.
	As of OpenSSL 1.1.0, compression is off by default.

	=item B<-no_comp>

	Disables support for SSL/TLS compression, same as setting
	B<SSL_OP_NO_COMPRESSION>.
	As of OpenSSL 1.1.0, compression is off by default.

	=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<-no_resumption_on_reneg>

	set SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION flag. 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>.

	=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 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<Certificate>

	Attempts to use the file B<value> as the certificate for the appropriate
	context. It currently uses SSL_CTX_use_certificate_chain_file() if an B<SSL_CTX>
	structure is set or SSL_use_certificate_file() with filetype PEM if an B<SSL>
	structure is set. This option is only supported if certificate operations
	are permitted.

	=item B<PrivateKey>

	Attempts to use the file B<value> as the private key for the appropriate
	context. This option is only supported if certificate operations
	are permitted. Note: if no B<PrivateKey> option is set then a private key is
	not loaded unless the B<SSL_CONF_FLAG_REQUIRE_PRIVATE> is set.

	=item B<ChainCAFile>, B<ChainCAPath>, B<VerifyCAFile>, B<VerifyCAPath>

	These options indicate a file or directory used for building certificate
	chains or verifying certificate chains. These options are only supported
	if certificate operations are permitted.

	=item B<ServerInfoFile>

	Attempts to use the file B<value> in the "serverinfo" extension using the
	function SSL_CTX_use_serverinfo_file.

	=item B<DHParameters>

	Attempts to use the file B<value> as the set of temporary DH parameters for
	the appropriate context. This option is only supported if certificate
	operations are permitted.

	=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<MinProtocol>

	This sets the minimum supported SSL, TLS or DTLS version.

	Currently supported protocol values are B<SSLv3>, B<TLSv1>, B<TLSv1.1>,
	B<TLSv1.2>, B<DTLSv1> and B<DTLSv1.2>.
	The value B<None> will disable the limit.

	=item B<MaxProtocol>

	This sets the maximum supported SSL, TLS or DTLS version.

	Currently supported protocol values are B<SSLv3>, B<TLSv1>, B<TLSv1.1>,
	B<TLSv1.2>, B<DTLSv1> and B<DTLSv1.2>.
	The value B<None> will disable the limit.

	=item B<Protocol>

	This can be used to enable or disable certain versions of the SSL,
	TLS or DTLS protocol.

	The B<value> argument is a comma separated list of supported protocols
	to enable or disable.
	If a protocol is preceded by B<-> that version is disabled.

	All protocol versions are enabled by default.
	You need to disable at least one protocol version for this setting have any
	effect.
	Only enabling some protocol versions does not disable the other protocol
	versions.

	Currently supported protocol values are B<SSLv3>, B<TLSv1>, B<TLSv1.1>,
	B<TLSv1.2>, B<DTLSv1> and B<DTLSv1.2>.
	The special value B<ALL> refers to all supported versions.

	This can't enable protocols that are disabled using B<MinProtocol>
	or B<MaxProtocol>, but can disable protocols that are still allowed
	by them.

	The B<Protocol> command is fragile and deprecated; do not use it.
	Use B<MinProtocol> and B<MaxProtocol> instead.
	If you do use B<Protocol>, make sure that the resulting range of enabled
	protocols has no "holes", e.g. if TLS 1.0 and TLS 1.2 are both enabled, make
	sure to also leave TLS 1.1 enabled.

	=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 L<SSL_CTX_set_options(3)> 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<NoResumptionOnRenegotiation> set
	B<SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION> flag. 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.

	=item B<VerifyMode>

	The B<value> argument is a comma separated list of flags to set.

	B<Peer> enables peer verification: for clients only.

	B<Request> requests but does not require a certificate from the client.
	Servers only.

	B<Require> requests and requires a certificate from the client: an error
	occurs if the client does not present a certificate. Servers only.

	B<Once> requests a certificate from a client only on the initial connection:
	not when renegotiating. Servers only.

	=item B<ClientCAFile>, B<ClientCAPath>

	A file or directory of certificates in PEM format whose names are used as the
	set of acceptable names for client CAs. Servers only. This option is only
	supported if certificate operations are permitted.

	=back

	=head1 SUPPORTED COMMAND TYPES

	The function SSL_CONF_cmd_value_type() currently returns one of the following
	types:

	=over 4

	=item B<SSL_CONF_TYPE_UNKNOWN>

	The B<cmd> string is unrecognised, this return value can be use to flag
	syntax errors.

	=item B<SSL_CONF_TYPE_STRING>

	The value is a string without any specific structure.

	=item B<SSL_CONF_TYPE_FILE>

	The value is a file name.

	=item B<SSL_CONF_TYPE_DIR>

	The value is a directory name.

	=item B<SSL_CONF_TYPE_NONE>

	The value string is not used e.g. a command line option which doesn't take an
	argument.

	=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", "-SSLv3");
	SSL_CONF_cmd(ctx, userparam, uservalue);

	it will disable SSLv3 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", "-SSLv3");

	SSLv3 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.

	The function SSL_CONF_cmd_value_type() can be used by applications to
	check for the existence of a command or to perform additional syntax
	checking or translation of the command value. For example if the return
	value is B<SSL_CONF_TYPE_FILE> an application could translate a relative
	pathname to an absolute pathname.

	=head1 EXAMPLES

	Set supported signature algorithms:

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

	There are various ways to select the supported protocols.

	This set the minimum protocol version to TLSv1, and so disables SSLv3.
	This is the recommended way to disable protocols.

	SSL_CONF_cmd(ctx, "MinProtocol", "TLSv1");

	The following also disables SSLv3:

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

	The following will first enable all protocols, and then disable
	SSLv3.
	If no protocol versions were disabled before this has the same effect as
	"-SSLv3", but if some versions were disables this will re-enable them before
	disabling SSLv3.

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

	Only enable TLSv1.2:

	SSL_CONF_cmd(ctx, "MinProtocol", "TLSv1.2");
	SSL_CONF_cmd(ctx, "MaxProtocol", "TLSv1.2");

	This also only enables TLSv1.2:

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

	Disable TLS session tickets:

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

	Enable compression:

	SSL_CONF_cmd(ctx, "Options", "Compression");

	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.

	SSL_CONF_finish() returns 1 for success and 0 for failure.

	=head1 SEE ALSO

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

	=head1 HISTORY

	SSL_CONF_cmd() was first added to OpenSSL 1.0.2

	B<SSL_OP_NO_SSL2> doesn't have effect since 1.1.0, but the macro is retained
	for backwards compatibility.

	B<SSL_CONF_TYPE_NONE> was first added to OpenSSL 1.1.0. In earlier versions of
	OpenSSL passing a command which didn't take an argument would return
	B<SSL_CONF_TYPE_UNKNOWN>.

	B<MinProtocol> and B<MaxProtocol> where added in OpenSSL 1.1.0.

	=head1 COPYRIGHT

	Copyright 2012-2016 The OpenSSL Project Authors. All Rights Reserved.

	Licensed under the OpenSSL license (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