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SSL_CTX_SET_OPTIONS(3ossl)          OpenSSL         SSL_CTX_SET_OPTIONS(3ossl)



NAME

       SSL_CTX_set_options, SSL_set_options, SSL_CTX_clear_options,
       SSL_clear_options, SSL_CTX_get_options, SSL_get_options,
       SSL_get_secure_renegotiation_support - manipulate SSL options


SYNOPSIS

        #include <openssl/ssl.h>

        uint64_t SSL_CTX_set_options(SSL_CTX *ctx, uint64_t options);
        uint64_t SSL_set_options(SSL *ssl, uint64_t options);

        uint64_t SSL_CTX_clear_options(SSL_CTX *ctx, uint64_t options);
        uint64_t SSL_clear_options(SSL *ssl, uint64_t options);

        uint64_t SSL_CTX_get_options(const SSL_CTX *ctx);
        uint64_t SSL_get_options(const SSL *ssl);

        long SSL_get_secure_renegotiation_support(SSL *ssl);


DESCRIPTION

       SSL_CTX_set_options(3) adds the options set via bit-mask in options to
       ctx.  Options already set before are not cleared!

       SSL_set_options() adds the options set via bit-mask in options to ssl.
       Options already set before are not cleared!

       SSL_CTX_clear_options() clears the options set via bit-mask in options
       to ctx.

       SSL_clear_options() clears the options set via bit-mask in options to
       ssl.

       SSL_CTX_get_options() returns the options set for ctx.

       SSL_get_options() returns the options set for ssl.

       SSL_get_secure_renegotiation_support() indicates whether the peer
       supports secure renegotiation.  Note, this is implemented via a macro.


NOTES

       The behaviour of the SSL library can be changed by setting several
       options.  The options are coded as bit-masks and can be combined by a
       bitwise or operation (|).

       SSL_CTX_set_options(3) and SSL_set_options() affect the (external)
       protocol behaviour of the SSL library. The (internal) behaviour of the
       API can be changed by using the similar SSL_CTX_set_mode(3) and
       SSL_set_mode() functions.

       During a handshake, the option settings of the SSL object are used.
       When a new SSL object is created from a context using SSL_new(), the
       current option setting is copied. Changes to ctx do not affect already
       created SSL objects. SSL_clear() does not affect the settings.

       The following bug workaround options are available:

       SSL_OP_CRYPTOPRO_TLSEXT_BUG
           Add server-hello extension from the early version of cryptopro
           draft when GOST ciphersuite is negotiated. Required for
           interoperability with CryptoPro CSP 3.x.

       SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS
           Disables a countermeasure against a SSL 3.0/TLS 1.0 protocol
           vulnerability affecting CBC ciphers, which cannot be handled by
           some broken SSL implementations.  This option has no effect for
           connections using other ciphers.

       SSL_OP_SAFARI_ECDHE_ECDSA_BUG
           Don't prefer ECDHE-ECDSA ciphers when the client appears to be
           Safari on OS X.  OS X 10.8..10.8.3 has broken support for
           ECDHE-ECDSA ciphers.

       SSL_OP_TLSEXT_PADDING
           Adds a padding extension to ensure the ClientHello size is never
           between 256 and 511 bytes in length. This is needed as a workaround
           for some implementations.

       SSL_OP_ALL
           All of the above bug workarounds.

       It is usually safe to use SSL_OP_ALL to enable the bug workaround
       options if compatibility with somewhat broken implementations is
       desired.

       The following modifying options are available:

       SSL_OP_ALLOW_CLIENT_RENEGOTIATION
           Client-initiated renegotiation is disabled by default. Use this
           option to enable it.

       SSL_OP_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.

       SSL_OP_PREFER_NO_DHE_KEX
           In TLSv1.3, on resumption let the server prefer a non-(ec)dhe based
           key exchange mode over an (ec)dhe based one. Ignored without
           SSL_OP_ALLOW_NO_DHE_KEX being set as well. Always ignored on the
           client.

       SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION
           Allow legacy insecure renegotiation between OpenSSL and unpatched
           clients or servers. See the SECURE RENEGOTIATION section for more
           details.

       SSL_OP_CIPHER_SERVER_PREFERENCE
           When choosing a cipher, use the server's preferences instead of the
           client preferences. When not set, the SSL server will always follow
           the clients preferences. When set, the SSL/TLS server will choose
           following its own preferences.

       SSL_OP_CISCO_ANYCONNECT
           Use Cisco's version identifier of DTLS_BAD_VER when establishing a
           DTLSv1 connection. Only available when using the deprecated
           DTLSv1_client_method() API.

       SSL_OP_CLEANSE_PLAINTEXT
           By default TLS and QUIC SSL objects keep a copy of received
           plaintext application data in a static buffer until it is
           overwritten by the next portion of data. When enabling
           SSL_OP_CLEANSE_PLAINTEXT deciphered application data is cleansed by
           calling OPENSSL_cleanse(3) after passing data to the application.
           Data is also cleansed when releasing the connection (e.g.
           SSL_free(3)).

           Since OpenSSL only cleanses internal buffers, the application is
           still responsible for cleansing all other buffers. Most notably,
           this applies to buffers passed to functions like SSL_read(3),
           SSL_peek(3) but also like SSL_write(3).

           TLS connections do not buffer data to be sent in plaintext. QUIC
           stream objects do buffer plaintext data to be sent and this option
           will also cause that data to be cleansed when it is discarded.

           This option can be set differently on individual QUIC stream
           objects and has no effect on QUIC connection objects (except where
           a default stream is being used).

       SSL_OP_COOKIE_EXCHANGE
           Turn on Cookie Exchange as described in RFC4347 Section 4.2.1. Only
           affects DTLS connections.

       SSL_OP_DISABLE_TLSEXT_CA_NAMES
           Disable TLS Extension CA Names. You may want to disable it for
           security reasons or for compatibility with some Windows TLS
           implementations crashing when this extension is larger than 1024
           bytes.

       SSL_OP_ENABLE_KTLS
           Enable the use of kernel TLS. In order to benefit from kernel TLS
           OpenSSL must have been compiled with support for it, and it must be
           supported by the negotiated ciphersuites and extensions. The
           specific ciphersuites and extensions that are supported may vary by
           platform and kernel version.

           The kernel TLS data-path implements the record layer, and the
           encryption algorithm. The kernel will utilize the best hardware
           available for encryption. Using the kernel data-path should reduce
           the memory footprint of OpenSSL because no buffering is required.
           Also, the throughput should improve because data copy is avoided
           when user data is encrypted into kernel memory instead of the usual
           encrypt then copy to kernel.

           Kernel TLS might not support all the features of OpenSSL. For
           instance, renegotiation, and setting the maximum fragment size is
           not possible as of Linux 4.20.

           Note that with kernel TLS enabled some cryptographic operations are
           performed by the kernel directly and not via any available OpenSSL
           Providers. This might be undesirable if, for example, the
           application requires all cryptographic operations to be performed
           by the FIPS provider.

       SSL_OP_ENABLE_KTLS_TX_ZEROCOPY_SENDFILE
           With this option, sendfile() will use the zerocopy mode, which
           gives a performance boost when used with KTLS hardware offload.
           Note that invalid TLS records might be transmitted if the file is
           changed while being sent. This option has no effect if
           SSL_OP_ENABLE_KTLS is not enabled.

           This option only applies to Linux. KTLS sendfile on FreeBSD doesn't
           offer an option to disable zerocopy and always runs in this mode.

       SSL_OP_ENABLE_MIDDLEBOX_COMPAT
           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. Regardless of whether this option is set or
           not CCS messages received from the peer will always be ignored in
           TLSv1.3. This option is set by default. To switch it off use
           SSL_clear_options(). A future version of OpenSSL may not set this
           by default.

       SSL_OP_IGNORE_UNEXPECTED_EOF
           Some TLS implementations do not send the mandatory close_notify
           alert on shutdown. If the application tries to wait for the
           close_notify alert but the peer closes the connection without
           sending it, an error is generated. When this option is enabled the
           peer does not need to send the close_notify alert and a closed
           connection will be treated as if the close_notify alert was
           received.

           You should only enable this option if the protocol running over TLS
           can detect a truncation attack itself, and that the application is
           checking for that truncation attack.

           For more information on shutting down a connection, see
           SSL_shutdown(3).

       SSL_OP_LEGACY_SERVER_CONNECT
           Allow legacy insecure renegotiation between OpenSSL and unpatched
           servers only. See the SECURE RENEGOTIATION section for more
           details.

       SSL_OP_NO_ANTI_REPLAY
           By default, when a server is configured for early data (i.e.,
           max_early_data > 0), OpenSSL will switch on replay protection. See
           SSL_read_early_data(3) for a description of the replay protection
           feature. 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. Those applications can turn
           this feature off by setting this option. This is a server-side
           option only. It is ignored by clients.

       SSL_OP_NO_TX_CERTIFICATE_COMPRESSION
           Normally clients and servers will transparently attempt to
           negotiate the RFC8879 certificate compression option on TLSv1.3
           connections.

           If this option is set, the certificate compression extension is
           ignored upon receipt and compressed certificates will not be sent
           to the peer.

       SSL_OP_NO_RX_CERTIFICATE_COMPRESSION
           Normally clients and servers will transparently attempt to
           negotiate the RFC8879 certificate compression option on TLSv1.3
           connections.

           If this option is set, the certificate compression extension will
           not be sent and compressed certificates will not be accepted from
           the peer.

       SSL_OP_NO_COMPRESSION
           Do not use TLS record compression even if it is supported. This
           option is set by default. To switch it off use SSL_clear_options().
           Note that TLS record compression is not recommended and is not
           available at security level 2 or above. From OpenSSL 3.2 the
           default security level is 2, so clearing this option will have no
           effect without also changing the default security level. See
           SSL_CTX_set_security_level(3).

       SSL_OP_NO_ENCRYPT_THEN_MAC
           Normally clients and servers will transparently attempt to
           negotiate the RFC7366 Encrypt-then-MAC option on TLS and DTLS
           connection.

           If this option is set, Encrypt-then-MAC is disabled. Clients will
           not propose, and servers will not accept the extension.

       SSL_OP_NO_EXTENDED_MASTER_SECRET
           Normally clients and servers will transparently attempt to
           negotiate the RFC7627 Extended Master Secret option on TLS and DTLS
           connection.

           If this option is set, Extended Master Secret is disabled. Clients
           will not propose, and servers will not accept the extension.

       SSL_OP_NO_QUERY_MTU
           Do not query the MTU. Only affects DTLS connections.

       SSL_OP_NO_RENEGOTIATION
           Disable all renegotiation in TLSv1.2 and earlier. Do not send
           HelloRequest messages, and ignore renegotiation requests via
           ClientHello.

       SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION
           When performing renegotiation as a server, always start a new
           session (i.e., session resumption requests are only accepted in the
           initial handshake). This option is not needed for clients.

       SSL_OP_NO_SSLv3, SSL_OP_NO_TLSv1, SSL_OP_NO_TLSv1_1, SSL_OP_NO_TLSv1_2,
       SSL_OP_NO_TLSv1_3, SSL_OP_NO_DTLSv1, SSL_OP_NO_DTLSv1_2
           These options turn off the SSLv3, TLSv1, TLSv1.1, TLSv1.2 or
           TLSv1.3 protocol versions with TLS or the DTLSv1, DTLSv1.2 versions
           with DTLS, respectively.  As of OpenSSL 1.1.0, these options are
           deprecated, use SSL_CTX_set_min_proto_version(3) and
           SSL_CTX_set_max_proto_version(3) instead.

       SSL_OP_NO_TICKET
           SSL/TLS supports two mechanisms for resuming sessions: session ids
           and stateless session tickets.

           When using session ids a copy of the session information is cached
           on the server and a unique id is sent to the client. When the
           client wishes to resume it provides the unique id so that the
           server can retrieve the session information from its cache.

           When using stateless session tickets the server uses a session
           ticket encryption key to encrypt the session information. This
           encrypted data is sent to the client as a "ticket". When the client
           wishes to resume it sends the encrypted data back to the server.
           The server uses its key to decrypt the data and resume the session.
           In this way the server can operate statelessly - no session
           information needs to be cached locally.

           The TLSv1.3 protocol only supports tickets and does not directly
           support session ids. However, OpenSSL allows two modes of ticket
           operation in TLSv1.3: stateful and stateless. Stateless tickets
           work the same way as in TLSv1.2 and below.  Stateful tickets mimic
           the session id behaviour available in TLSv1.2 and below.  The
           session information is cached on the server and the session id is
           wrapped up in a ticket and sent back to the client. When the client
           wishes to resume, it presents a ticket in the same way as for
           stateless tickets. The server can then extract the session id from
           the ticket and retrieve the session information from its cache.

           By default OpenSSL will use stateless tickets. The SSL_OP_NO_TICKET
           option will cause stateless tickets to not be issued. In TLSv1.2
           and below this means no ticket gets sent to the client at all. In
           TLSv1.3 a stateful ticket will be sent. This is a server-side
           option only.

           In TLSv1.3 it is possible to suppress all tickets (stateful and
           stateless) from being sent by calling SSL_CTX_set_num_tickets(3) or
           SSL_set_num_tickets(3).

       SSL_OP_PRIORITIZE_CHACHA
           When SSL_OP_CIPHER_SERVER_PREFERENCE is set, temporarily
           reprioritize ChaCha20-Poly1305 ciphers to the top of the server
           cipher list if a ChaCha20-Poly1305 cipher is at the top of the
           client cipher list. This helps those clients (e.g. mobile) use
           ChaCha20-Poly1305 if that cipher is anywhere in the server cipher
           list; but still allows other clients to use AES and other ciphers.
           Requires SSL_OP_CIPHER_SERVER_PREFERENCE.

       SSL_OP_TLS_ROLLBACK_BUG
           Disable version rollback attack detection.

           During the client key exchange, the client must send the same
           information about acceptable SSL/TLS protocol levels as during the
           first hello. Some clients violate this rule by adapting to the
           server's answer. (Example: the client sends a SSLv2 hello and
           accepts up to SSLv3.1=TLSv1, the server only understands up to
           SSLv3. In this case the client must still use the same
           SSLv3.1=TLSv1 announcement. Some clients step down to SSLv3 with
           respect to the server's answer and violate the version rollback
           protection.)

       The following options no longer have any effect but their identifiers
       are retained for compatibility purposes:

       SSL_OP_NETSCAPE_REUSE_CIPHER_CHANGE_BUG
       SSL_OP_MICROSOFT_BIG_SSLV3_BUFFER
       SSL_OP_SSLEAY_080_CLIENT_DH_BUG
       SSL_OP_TLS_D5_BUG
       SSL_OP_TLS_BLOCK_PADDING_BUG
       SSL_OP_MSIE_SSLV2_RSA_PADDING
       SSL_OP_SSLREF2_REUSE_CERT_TYPE_BUG
       SSL_OP_MICROSOFT_SESS_ID_BUG
       SSL_OP_NETSCAPE_CHALLENGE_BUG
       SSL_OP_PKCS1_CHECK_1
       SSL_OP_PKCS1_CHECK_2
       SSL_OP_SINGLE_DH_USE
       SSL_OP_SINGLE_ECDH_USE
       SSL_OP_EPHEMERAL_RSA
       SSL_OP_NETSCAPE_CA_DN_BUG
       SSL_OP_NETSCAPE_DEMO_CIPHER_CHANGE_BUG


SECURE RENEGOTIATION

       OpenSSL always attempts to use secure renegotiation as described in
       RFC5746. This counters the prefix attack described in CVE-2009-3555 and
       elsewhere.

       This attack has far reaching consequences which application writers
       should be aware of. In the description below an implementation
       supporting secure renegotiation is referred to as patched. A server not
       supporting secure renegotiation is referred to as unpatched.

       The following sections describe the operations permitted by OpenSSL's
       secure renegotiation implementation.

   Patched client and server
       Connections and renegotiation are always permitted by OpenSSL
       implementations.

   Unpatched client and patched OpenSSL server
       The initial connection succeeds but client renegotiation is denied by
       the server with a no_renegotiation warning alert if TLS v1.0 is used or
       a fatal handshake_failure alert in SSL v3.0.

       If the patched OpenSSL server attempts to renegotiate a fatal
       handshake_failure alert is sent. This is because the server code may be
       unaware of the unpatched nature of the client.

       If the option SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION is set then
       renegotiation always succeeds.

   Patched OpenSSL client and unpatched server
       If the option SSL_OP_LEGACY_SERVER_CONNECT or
       SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION is set then initial
       connections and renegotiation between patched OpenSSL clients and
       unpatched servers succeeds. If neither option is set then initial
       connections to unpatched servers will fail.

       Setting the option SSL_OP_LEGACY_SERVER_CONNECT has security
       implications; clients that are willing to connect to servers that do
       not implement RFC 5746 secure renegotiation are subject to attacks such
       as CVE-2009-3555.

       OpenSSL client applications wishing to ensure they can connect to
       unpatched servers should always set SSL_OP_LEGACY_SERVER_CONNECT

       OpenSSL client applications that want to ensure they can not connect to
       unpatched servers (and thus avoid any security issues) should always
       clear SSL_OP_LEGACY_SERVER_CONNECT using SSL_CTX_clear_options() or
       SSL_clear_options().

       The difference between the SSL_OP_LEGACY_SERVER_CONNECT and
       SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION options is that
       SSL_OP_LEGACY_SERVER_CONNECT enables initial connections and secure
       renegotiation between OpenSSL clients and unpatched servers only, while
       SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION allows initial connections and
       renegotiation between OpenSSL and unpatched clients or servers.

   Applicability of options to QUIC connections and streams
       These options apply to SSL objects referencing a QUIC connection:

       SSL_OP_ALLOW_NO_DHE_KEX
       SSL_OP_NO_TX_CERTIFICATE_COMPRESSION
       SSL_OP_NO_RX_CERTIFICATE_COMPRESSION
       SSL_OP_NO_TICKET
       SSL_OP_PRIORITIZE_CHACHA

       These options apply to SSL objects referencing a QUIC stream:

       SSL_OP_CLEANSE_PLAINTEXT

       Options on QUIC connections are initialized from the options set on
       SSL_CTX before a QUIC connection SSL object is created. Options on QUIC
       streams are initialised from the options configured on the QUIC
       connection SSL object they are created from.

       Setting options which relate to QUIC streams on a QUIC connection SSL
       object has no direct effect on the QUIC connection SSL object itself,
       but will change the options set on the default stream (if there is one)
       and will also determine the default options set on any future streams
       which are created.

       Other options not mentioned above do not have an effect and will be
       ignored.

       Options which relate to QUIC streams may also be set directly on QUIC
       stream SSL objects. Setting connection-related options on such an
       object has no effect.


RETURN VALUES

       SSL_CTX_set_options(3) and SSL_set_options() return the new options
       bit-mask after adding options.

       SSL_CTX_clear_options() and SSL_clear_options() return the new options
       bit-mask after clearing options.

       SSL_CTX_get_options() and SSL_get_options() return the current
       bit-mask.

       SSL_get_secure_renegotiation_support() returns 1 is the peer supports
       secure renegotiation and 0 if it does not.


SEE ALSO

       ssl(7), SSL_new(3), SSL_clear(3), SSL_shutdown(3)
       SSL_CTX_set_tmp_dh_callback(3), SSL_CTX_set_min_proto_version(3),
       openssl-dhparam(1)


HISTORY

       The attempt to always try to use secure renegotiation was added in
       OpenSSL 0.9.8m.

       The SSL_OP_PRIORITIZE_CHACHA and SSL_OP_NO_RENEGOTIATION options were
       added in OpenSSL 1.1.1.

       The SSL_OP_NO_EXTENDED_MASTER_SECRET and SSL_OP_IGNORE_UNEXPECTED_EOF
       options were added in OpenSSL 3.0.

       The SSL_OP_ constants and the corresponding parameter and return values
       of the affected functions were changed to "uint64_t" type in OpenSSL
       3.0.  For that reason it is no longer possible use the SSL_OP_ macro
       values in preprocessor "#if" conditions. However it is still possible
       to test whether these macros are defined or not.


COPYRIGHT

       Copyright 2001-2023 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>.

3.3.2                             2024-09-04        SSL_CTX_SET_OPTIONS(3ossl)

openssl 3.3.2 - Generated Sun Sep 22 06:39:02 CDT 2024
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