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SSL_CONF_cmd(3)                     OpenSSL                    SSL_CONF_cmd(3)



NAME
       SSL_CONF_cmd_value_type, SSL_CONF_cmd - send configuration command

LIBRARY
       libcrypto, -lcrypto

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);

DESCRIPTION
       The function SSL_CONF_cmd() performs configuration operation cmd with
       optional parameter value on ctx. Its purpose is to simplify application
       configuration of SSL_CTX or 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 cmd refers to.

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

       -sigalgs
           This sets the supported signature algorithms for TLSv1.2 and
           TLSv1.3.  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 value argument should be a colon separated list of signature
           algorithms in order of decreasing preference of the form
           algorithm+hash or signature_scheme. algorithm is one of RSA, DSA or
           ECDSA and hash is a supported algorithm OID short name such as
           SHA1, SHA224, SHA256, SHA384 of SHA512.  Note: algorithm and hash
           names are case sensitive.  signature_scheme is one of the signature
           schemes defined in TLSv1.3, specified using the IETF name, e.g.,
           ecdsa_secp256r1_sha256, ed25519, or rsa_pss_pss_sha256.

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

           Note: algorithms which specify a PKCS#1 v1.5 signature scheme
           (either by using RSA as the algorithm or by using one of the
           rsa_pkcs1_* identifiers) are ignored in TLSv1.3 and will not be
           negotiated.

       -client_sigalgs
           This sets the supported signature algorithms associated with client
           authentication for TLSv1.2 and TLSv1.3.  For servers the value is
           used in the signature_algorithms field of a CertificateRequest
           message.  For clients it is used to determine which signature
           algorithm to use with the client certificate.  If a server does not
           request a certificate this option has no effect.

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

       -groups
           This sets the supported groups. For clients, the groups are sent
           using the supported groups extension. For servers, it is used to
           determine which group to use. This setting affects groups used for
           signatures (in TLSv1.2 and earlier) and key exchange. The first
           group listed will also be used for the key_share sent by a client
           in a TLSv1.3 ClientHello.

           The value argument is a colon separated list of groups. The group
           can be either the NIST name (e.g. P-256), some other commonly used
           name where applicable (e.g. X25519) or an OpenSSL OID name (e.g
           prime256v1). Group names are case sensitive. The list should be in
           order of preference with the most preferred group first.

       -curves
           This is a synonym for the "-groups" command.

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

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

       -cipher
           Sets the TLSv1.2 and below ciphersuite list to value. This list
           will be combined with any configured TLSv1.3 ciphersuites. Note:
           syntax checking of value is currently not performed unless a SSL or
           SSL_CTX structure is associated with cctx.

       -ciphersuites
           Sets the available ciphersuites for TLSv1.3 to value. This is a
           simple colon (":") separated list of TLSv1.3 ciphersuite names in
           order of preference. This list will be combined any configured
           TLSv1.2 and below ciphersuites.  See openssl_ciphers(1) for more
           information.

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

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

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

       -record_padding
           Attempts to pad TLSv1.3 records so that they are a multiple of
           value in length on send. A value of 0 or 1 turns off padding.
           Otherwise, the value must be >1 or <=16384.

       -no_renegotiation
           Disables all attempts at renegotiation in TLSv1.2 and earlier, same
           as setting SSL_OP_NO_RENEGOTIATION.

       -min_protocol, -max_protocol
           Sets the minimum and maximum supported protocol.  Currently
           supported protocol values are SSLv3, TLSv1, TLSv1.1, TLSv1.2,
           TLSv1.3 for TLS and DTLSv1, DTLSv1.2 for DTLS, and None for no
           limit.  If 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.

       -no_ssl3, -no_tls1, -no_tls1_1, -no_tls1_2, -no_tls1_3
           Disables protocol support for SSLv3, TLSv1.0, TLSv1.1, TLSv1.2 or
           TLSv1.3 by setting the corresponding options SSL_OP_NO_SSLv3,
           SSL_OP_NO_TLSv1, SSL_OP_NO_TLSv1_1, SSL_OP_NO_TLSv1_2 and
           SSL_OP_NO_TLSv1_3 respectively. These options are deprecated,
           instead use -min_protocol and -max_protocol.

       -bugs
           Various bug workarounds are set, same as setting SSL_OP_ALL.

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

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

       -no_ticket
           Disables support for session tickets, same as setting
           SSL_OP_NO_TICKET.

       -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
           SSL_OP_CIPHER_SERVER_PREFERENCE. Only used by servers.

       -prioritize_chacha
           Prioritize ChaCha ciphers when the client has a ChaCha20 cipher at
           the top of its preference list. This usually indicates a client
           without AES hardware acceleration (e.g. mobile) is in use.
           Equivalent to SSL_OP_PRIORITIZE_CHACHA.  Only used by servers.
           Requires -serverpref.

       -no_resumption_on_reneg
           set SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION flag. Only used
           by servers.

       -legacyrenegotiation
           permits the use of unsafe legacy renegotiation. Equivalent to
           setting SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION.

       -legacy_server_connect, -no_legacy_server_connect
           permits or prohibits the use of unsafe legacy renegotiation for
           OpenSSL clients only. Equivalent to setting or clearing
           SSL_OP_LEGACY_SERVER_CONNECT.  Set by default.

       -allow_no_dhe_kex
           In TLSv1.3 allow a non-(ec)dhe based key exchange mode on
           resumption. This means that there will be no forward secrecy for
           the resumed session.

       -strict
           enables strict mode protocol handling. Equivalent to setting
           SSL_CERT_FLAG_TLS_STRICT.

       -anti_replay, -no_anti_replay
           Switches replay protection, on or off respectively. With replay
           protection on, OpenSSL will automatically detect if a session
           ticket has been used more than once, TLSv1.3 has been negotiated,
           and early data is enabled on the server. A full handshake is forced
           if a session ticket is used a second or subsequent time. Anti-
           Replay is on by default unless overridden by a configuration file
           and is only used by servers. Anti-replay measures are required for
           compliance with the TLSv1.3 specification. Some applications may be
           able to mitigate the replay risks in other ways and in such cases
           the built-in OpenSSL functionality is not required. Switching off
           anti-replay is equivalent to SSL_OP_NO_ANTI_REPLAY.

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

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

       CipherString
           Sets the ciphersuite list for TLSv1.2 and below to value. This list
           will be combined with any configured TLSv1.3 ciphersuites. Note:
           syntax checking of value is currently not performed unless an SSL
           or SSL_CTX structure is associated with cctx.

       Ciphersuites
           Sets the available ciphersuites for TLSv1.3 to value. This is a
           simple colon (":") separated list of TLSv1.3 ciphersuite names in
           order of preference. This list will be combined any configured
           TLSv1.2 and below ciphersuites.  See openssl_ciphers(1) for more
           information.

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

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

       ChainCAFile, ChainCAPath, VerifyCAFile, 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.

       RequestCAFile
           This option indicates a file containing a set of certificates in
           PEM form.  The subject names of the certificates are sent to the
           peer in the certificate_authorities extension for TLS 1.3 (in
           ClientHello or CertificateRequest) or in a certificate request for
           previous versions or TLS.

       ServerInfoFile
           Attempts to use the file value in the "serverinfo" extension using
           the function SSL_CTX_use_serverinfo_file.

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

       RecordPadding
           Attempts to pad TLSv1.3 records so that they are a multiple of
           value in length on send. A value of 0 or 1 turns off padding.
           Otherwise, the value must be >1 or <=16384.

       NoRenegotiation
           Disables all attempts at renegotiation in TLSv1.2 and earlier, same
           as setting SSL_OP_NO_RENEGOTIATION.

       SignatureAlgorithms
           This sets the supported signature algorithms for TLSv1.2 and
           TLSv1.3.  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 value argument should be a colon separated list of signature
           algorithms in order of decreasing preference of the form
           algorithm+hash or signature_scheme. algorithm is one of RSA, DSA or
           ECDSA and hash is a supported algorithm OID short name such as
           SHA1, SHA224, SHA256, SHA384 of SHA512.  Note: algorithm and hash
           names are case sensitive.  signature_scheme is one of the signature
           schemes defined in TLSv1.3, specified using the IETF name, e.g.,
           ecdsa_secp256r1_sha256, ed25519, or rsa_pss_pss_sha256.

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

           Note: algorithms which specify a PKCS#1 v1.5 signature scheme
           (either by using RSA as the algorithm or by using one of the
           rsa_pkcs1_* identifiers) are ignored in TLSv1.3 and will not be
           negotiated.

       ClientSignatureAlgorithms
           This sets the supported signature algorithms associated with client
           authentication for TLSv1.2 and TLSv1.3.  For servers the value is
           used in the signature_algorithms field of a CertificateRequest
           message.  For clients it is used to determine which signature
           algorithm to use with the client certificate.  If a server does not
           request a certificate this option has no effect.

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

       Groups
           This sets the supported groups. For clients, the groups are sent
           using the supported groups extension. For servers, it is used to
           determine which group to use. This setting affects groups used for
           signatures (in TLSv1.2 and earlier) and key exchange. The first
           group listed will also be used for the key_share sent by a client
           in a TLSv1.3 ClientHello.

           The value argument is a colon separated list of groups. The group
           can be either the NIST name (e.g. P-256), some other commonly used
           name where applicable (e.g. X25519) or an OpenSSL OID name (e.g
           prime256v1). Group names are case sensitive. The list should be in
           order of preference with the most preferred group first.

       Curves
           This is a synonym for the "Groups" command.

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

           Currently supported protocol values are SSLv3, TLSv1, TLSv1.1,
           TLSv1.2, TLSv1.3, DTLSv1 and DTLSv1.2.  The value None will disable
           the limit.

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

           Currently supported protocol values are SSLv3, TLSv1, TLSv1.1,
           TLSv1.2, TLSv1.3, DTLSv1 and DTLSv1.2.  The value None will disable
           the limit.

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

           The value argument is a comma separated list of supported protocols
           to enable or disable.  If a protocol is preceded by - 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 SSLv3, TLSv1, TLSv1.1,
           TLSv1.2, TLSv1.3, DTLSv1 and DTLSv1.2.  The special value ALL
           refers to all supported versions.

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

           The Protocol command is fragile and deprecated; do not use it.  Use
           MinProtocol and MaxProtocol instead.  If you do use 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.

       Options
           The value argument is a comma separated list of various flags to
           set.  If a flag string is preceded - it is disabled.  See the
           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 -flag syntax is needed to disable it.

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

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

           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 SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS.

           Bugs: enable various bug workarounds. Same as SSL_OP_ALL.

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

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

           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
           SSL_OP_CIPHER_SERVER_PREFERENCE. Only used by servers.

           PrioritizeChaCha: prioritizes ChaCha ciphers when the client has a
           ChaCha20 cipher at the top of its preference list. This usually
           indicates a mobile client is in use. Equivalent to
           SSL_OP_PRIORITIZE_CHACHA.  Only used by servers.

           NoResumptionOnRenegotiation: set
           SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION flag. Only used by
           servers.

           UnsafeLegacyRenegotiation: permits the use of unsafe legacy
           renegotiation.  Equivalent to
           SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION.

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

           EncryptThenMac: use encrypt-then-mac extension, enabled by default.
           Inverse of SSL_OP_NO_ENCRYPT_THEN_MAC: that is, -EncryptThenMac is
           the same as setting SSL_OP_NO_ENCRYPT_THEN_MAC.

           AllowNoDHEKEX: In TLSv1.3 allow a non-(ec)dhe based key exchange
           mode on resumption. This means that there will be no forward
           secrecy for the resumed session. Equivalent to
           SSL_OP_ALLOW_NO_DHE_KEX.

           MiddleboxCompat: If set then dummy Change Cipher Spec (CCS)
           messages are sent in TLSv1.3. This has the effect of making TLSv1.3
           look more like TLSv1.2 so that middleboxes that do not understand
           TLSv1.3 will not drop the connection. This option is set by
           default. A future version of OpenSSL may not set this by default.
           Equivalent to SSL_OP_ENABLE_MIDDLEBOX_COMPAT.

           AntiReplay: If set then OpenSSL will automatically detect if a
           session ticket has been used more than once, TLSv1.3 has been
           negotiated, and early data is enabled on the server. A full
           handshake is forced if a session ticket is used a second or
           subsequent time. This option is set by default and is only used by
           servers. Anti-replay measures are required to comply with the
           TLSv1.3 specification. Some applications may be able to mitigate
           the replay risks in other ways and in such cases the built-in
           OpenSSL functionality is not required.  Disabling anti-replay is
           equivalent to setting SSL_OP_NO_ANTI_REPLAY.

       VerifyMode
           The value argument is a comma separated list of flags to set.

           Peer enables peer verification: for clients only.

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

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

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

           RequestPostHandshake configures the connection to support requests
           but does not require a certificate from the client post-handshake.
           A certificate will not be requested during the initial handshake.
           The server application must provide a mechanism to request a
           certificate post-handshake. Servers only.  TLSv1.3 only.

           RequiresPostHandshake configures the connection to support requests
           and requires a certificate from the client post-handshake: an error
           occurs if the client does not present a certificate. A certificate
           will not be requested during the initial handshake. The server
           application must provide a mechanism to request a certificate post-
           handshake. Servers only. TLSv1.3 only.

       ClientCAFile, 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.

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

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

       SSL_CONF_TYPE_STRING
           The value is a string without any specific structure.

       SSL_CONF_TYPE_FILE
           The value is a file name.

       SSL_CONF_TYPE_DIR
           The value is a directory name.

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

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 always disabled and attempt to override this by the user are
       ignored.

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

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

       Applications can also use SSL_CONF_cmd() to process command lines
       though the utility function SSL_CONF_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
       cmd and the following argument to 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_CONF_cmd().
       If -2 is returned then 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 SSL_CONF_TYPE_FILE an application could translate a relative
       pathname to an absolute pathname.

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");

RETURN VALUES
       SSL_CONF_cmd() returns 1 if the value of cmd is recognised and value is
       NOT used and 2 if both cmd and 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 cmd is not recognised.

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

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

SEE ALSO
       SSL_CONF_CTX_new(3), SSL_CONF_CTX_set_flags(3),
       SSL_CONF_CTX_set1_prefix(3), SSL_CONF_CTX_set_ssl_ctx(3),
       SSL_CONF_cmd_argv(3), SSL_CTX_set_options(3)

HISTORY
       SSL_CONF_cmd() was first added to OpenSSL 1.0.2

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

       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 SSL_CONF_TYPE_UNKNOWN.

       MinProtocol and MaxProtocol where added in OpenSSL 1.1.0.

       AllowNoDHEKEX and PrioritizeChaCha were added in OpenSSL 1.1.1.

COPYRIGHT
       Copyright 2012-2018 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
       <https://www.openssl.org/source/license.html>.



1.1.1                             2018-09-17                   SSL_CONF_cmd(3)