Ubuntu Manpage: SSL_CONF_cmd_value_type, SSL_CONF_cmd

Provided by: libssl-doc_3.0.2-0ubuntu1.15_all

NAME

       SSL_CONF_cmd_value_type, SSL_CONF_cmd - send configuration command

SYNOPSIS

        #include <openssl/ssl.h>

        int SSL_CONF_cmd(SSL_CONF_CTX *ctx, const char *option, const char *value);
        int SSL_CONF_cmd_value_type(SSL_CONF_CTX *ctx, const char *option);

DESCRIPTION

       The function SSL_CONF_cmd() performs configuration operation option 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 option refers to.

SUPPORTED COMMAND LINE COMMANDS

Currently supported option names for command lines (i.e. when the flag
SSL_CONF_FLAG_CMDLINE is set) are listed below. Note: all option 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.

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

-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.

-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_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.

-client_renegotiation
Allows servers to accept client-initiated renegotiation. Equivalent to setting
SSL_OP_ALLOW_CLIENT_RENEGOTIATION. Only used by servers.

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

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

-no_resumption_on_reneg
Sets SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION. Only used by servers.

-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.

-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.

-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.

-sigalgs algs
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 algs 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 algs
This sets the supported signature algorithms associated with client authentication for
TLSv1.2 and TLSv1.3. For servers the algs 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 algs is identical to -sigalgs. If not set, then the value set for
-sigalgs will be used instead.

-groups 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 groups 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,
ffdhe2048) 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.

Currently supported groups for TLSv1.3 are P-256, P-384, P-521, X25519, X448,
ffdhe2048, ffdhe3072, ffdhe4096, ffdhe6144, ffdhe8192.

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

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

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

-ciphersuites 1.3ciphers
Sets the available ciphersuites for TLSv1.3 to value. This is a 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.

-min_protocol minprot, -max_protocol maxprot
Sets the minimum and maximum supported protocol. Currently supported protocol values
are SSLv3, TLSv1, TLSv1.1, TLSv1.2, TLSv1.3 for TLS; DTLSv1, DTLSv1.2 for DTLS, and
None for no limit. If either the lower or upper bound is not specified then only the
other bound applies, if specified. If your application supports both TLS and DTLS you
can specify any of these options twice, once with a bound for TLS and again with an
appropriate bound for DTLS. To restrict the supported protocol versions use these
commands rather than the deprecated alternative commands below.

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

-debug_broken_protocol
Ignored.

-no_middlebox
Turn off "middlebox compatibility", as described below.

Additional Options
The following options are accepted by SSL_CONF_cmd(), but are not processed by the OpenSSL
commands.

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

-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,
use -min_protocol and -max_protocol instead.

-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 option names for configuration files (i.e., when the flag
SSL_CONF_FLAG_FILE is set) are listed below. All configuration file option 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 option 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 ctx.

Ciphersuites
Sets the available ciphersuites for TLSv1.3 to value. This is a 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.

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,
ffdhe2048) 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.

Currently supported groups for TLSv1.3 are P-256, P-384, P-521, X25519, X448,
ffdhe2048, ffdhe3072, ffdhe4096, ffdhe6144, ffdhe8192.

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 SSL and TLS bounds apply only to TLS-based contexts, while
the DTLS bounds apply only to DTLS-based contexts. The command can be repeated with
one instance setting a TLS bound, and the other setting a DTLS bound. The value None
applies to both types of contexts and disables the limits.

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

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, disabled 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.

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

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.

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.

ExtendedMasterSecret: use extended master secret extension, enabled by default.
Inverse of SSL_OP_NO_EXTENDED_MASTER_SECRET: that is, -ExtendedMasterSecret is the
same as setting SSL_OP_NO_EXTENDED_MASTER_SECRET.

CANames: use CA names extension, enabled by default. Inverse of
SSL_OP_DISABLE_TLSEXT_CA_NAMES: that is, -CANames is the same as setting
SSL_OP_DISABLE_TLSEXT_CA_NAMES.

KTLS: Enables kernel TLS if support has been compiled in, and it is supported by the
negotiated ciphersuites and extensions. Equivalent to SSL_OP_ENABLE_KTLS.

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 option 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 filename.

       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 option 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 option 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 option 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.

RETURN VALUES

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

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

       A return code of 0 indicates that both option 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.

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");

HISTORY

       The SSL_CONF_cmd() function was added in OpenSSL 1.0.2.

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

       The SSL_CONF_TYPE_NONE was added in 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.

       The UnsafeLegacyServerConnect option is no longer set by default from OpenSSL 3.0.

COPYRIGHT

       Copyright 2012-2022 The OpenSSL Project Authors. All Rights Reserved.

       Licensed under the Apache License 2.0 (the "License").  You may not use this file except
       in compliance with the License.  You can obtain a copy in the file LICENSE in the source
       distribution or at <https://www.openssl.org/source/license.html>.