SSL_CONF_CMD(3SSL)

NAME
SSL_CONF_cmd_value_type, SSL_CONF_finish, SSL_CONF_cmd - send configuration command

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);

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.

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.

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 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 value argument should be a colon separated list of signature algorithms in order of decreasing preference of the form algorithm+hash. 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.

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

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

-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 value argument is a colon separated list of curves. 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.

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

-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.

-min_protocol, -max_protocol
    Sets the minimum and maximum supported protocol. Currently supported protocol values are SSLv3, TLSv1, TLSv1.1, TLSv1.2 for TLS and DTLSv1, DTLSv1.2 for DTLS, and 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.

-no_ssl3, -no_tls1, -no_tls1_1, -no_tls1_2
    Disables protocol support for SSLv3, TLSv1.0, TLSv1.1 or TLSv1.2 by setting the corresponding options SSL_OP_NO_SSLv3, SSL_OP_NO_TLSv1, SSL_OP_NO_TLSv1_1 and SSL_OP_NO_TLSv1_2 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.

-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.

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

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

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.

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.

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 value argument should be a colon separated list of signature algorithms in order of decreasing preference of the form algorithm+hash. 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.

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

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

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 value argument is a colon separated list of curves. 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.

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

    Currently supported protocol values are SSLv3, TLSv1, TLSv1.1, TLSv1.2, 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, 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, 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.

    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.

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.

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_CTX_cmd() it is possible to query if a given 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 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_CTX_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");

Set automatic support for any elliptic curve for key exchange:

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

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.

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

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.

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 <https://www.openssl.org/source/license.html>.