#use wml::openssl-macros area=docs page=SSL_CTX_set_options

<title>Documents, SSL_CTX_set_options(3)</title>

<h1>SSL_CTX_set_options(3)</h1>

#use wml::imp::generic

{:
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<!-- INDEX BEGIN -->

<UL>

	<LI><A HREF="#NAME">NAME</A>
	<LI><A HREF="#SYNOPSIS">SYNOPSIS</A>
	<LI><A HREF="#DESCRIPTION">DESCRIPTION</A>
	<LI><A HREF="#NOTES">NOTES</A>
	<LI><A HREF="#RETURN_VALUES">RETURN VALUES</A>
	<LI><A HREF="#SEE_ALSO">SEE ALSO</A>
	<LI><A HREF="#HISTORY">HISTORY</A>
</UL>
<!-- INDEX END -->

<HR>
<P>
<HR>
<H1><A NAME="NAME">NAME</A></H1>
<P>
SSL_CTX_set_options, SSL_set_options, SSL_CTX_get_options, SSL_get_options
- manipulate SSL engine options

</P>
<P>
<HR>
<H1><A NAME="SYNOPSIS">SYNOPSIS</A></H1>
<PRE> #include &lt;openssl/ssl.h&gt;
</PRE>
<PRE> long SSL_CTX_set_options(SSL_CTX *ctx, long options);
 long SSL_set_options(SSL *ssl, long options);
</PRE>
<PRE> long SSL_CTX_get_options(SSL_CTX *ctx);
 long SSL_get_options(SSL *ssl);
</PRE>
<P>
<HR>
<H1><A NAME="DESCRIPTION">DESCRIPTION</A></H1>
<P>
<CODE>SSL_CTX_set_options()</CODE> adds the options set via bitmask in <STRONG>options</STRONG> to <STRONG>ctx</STRONG>. Options already set before are not cleared!

</P>
<P>
<CODE>SSL_set_options()</CODE> adds the options set via bitmask in <STRONG>options</STRONG> to <STRONG>ssl</STRONG>. Options already set before are not cleared!

</P>
<P>
<CODE>SSL_CTX_get_options()</CODE> returns the options set for <STRONG>ctx</STRONG>.

</P>
<P>
<CODE>SSL_get_options()</CODE> returns the options set for <STRONG>ssl</STRONG>.

</P>
<P>
<HR>
<H1><A NAME="NOTES">NOTES</A></H1>
<P>
The behaviour of the SSL library can be changed by setting several options.
The options are coded as bitmasks and can be combined by a logical <STRONG>or</STRONG>
operation (|). Options can only be added but can never be reset.

</P>
<P>
<CODE>SSL_CTX_set_options()</CODE> and <CODE>SSL_set_options()</CODE>
affect the (external) protocol behaviour of the SSL library. The (internal)
behaviour of the API can be changed by using the similar
<A HREF="../ssl/SSL_CTX_set_mode.html#">SSL_CTX_set_mode(3)</A> and <CODE>SSL_set_mode()</CODE> functions.

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

</P>
<P>
The following <STRONG>bug workaround</STRONG> options are available:

</P>
<DL>
<DT><STRONG><A NAME="item_SSL_OP_MICROSOFT_SESS_ID_BUG">SSL_OP_MICROSOFT_SESS_ID_BUG</A></STRONG><DD>
<P>
www.microsoft.com - when talking SSLv2, if session-id reuse is performed,
the session-id passed back in the server-finished message is different from
the one decided upon.

</P>
<DT><STRONG><A NAME="item_SSL_OP_NETSCAPE_CHALLENGE_BUG">SSL_OP_NETSCAPE_CHALLENGE_BUG</A></STRONG><DD>
<P>
Netscape-Commerce/1.12, when talking SSLv2, accepts a 32 byte challenge but
then appears to only use 16 bytes when generating the encryption keys.
Using 16 bytes is ok but it should be ok to use 32. According to the SSLv3
spec, one should use 32 bytes for the challenge when operating in SSLv2/v3
compatibility mode, but as mentioned above, this breaks this server so 16
bytes is the way to go.

</P>
<DT><STRONG><A NAME="item_SSL_OP_NETSCAPE_REUSE_CIPHER_CHA">SSL_OP_NETSCAPE_REUSE_CIPHER_CHANGE_BUG</A></STRONG><DD>
<P>
ssl3.netscape.com:443, first a connection is established with RC4-MD5. If
it is then resumed, we end up using DES-CBC3-SHA. It should be RC4-MD5
according to 7.6.1.3, 'cipher_suite'.

</P>
<P>
Netscape-Enterprise/2.01 (https://merchant.netscape.com) has this bug. It
only really shows up when connecting via SSLv2/v3 then reconnecting via
SSLv3. The cipher list changes....

</P>
<P>
NEW INFORMATION. Try connecting with a cipher list of just
DES-CBC-SHA:RC4-MD5. For some weird reason, each new connection uses
RC4-MD5, but a re-connect tries to use DES-CBC-SHA. So netscape, when doing
a re-connect, always takes the first cipher in the cipher list.

</P>
<DT><STRONG><A NAME="item_SSL_OP_SSLREF2_REUSE_CERT_TYPE_B">SSL_OP_SSLREF2_REUSE_CERT_TYPE_BUG</A></STRONG><DD>
<P>
...

</P>
<DT><STRONG><A NAME="item_SSL_OP_MICROSOFT_BIG_SSLV3_BUFFE">SSL_OP_MICROSOFT_BIG_SSLV3_BUFFER</A></STRONG><DD>
<P>
...

</P>
<DT><STRONG><A NAME="item_SSL_OP_MSIE_SSLV2_RSA_PADDING">SSL_OP_MSIE_SSLV2_RSA_PADDING</A></STRONG><DD>
<P>
As of OpenSSL 0.9.7h and 0.9.8a, this option has no effect.

</P>
<DT><STRONG><A NAME="item_SSL_OP_SSLEAY_080_CLIENT_DH_BUG">SSL_OP_SSLEAY_080_CLIENT_DH_BUG</A></STRONG><DD>
<P>
...

</P>
<DT><STRONG><A NAME="item_SSL_OP_TLS_D5_BUG">SSL_OP_TLS_D5_BUG</A></STRONG><DD>
<P>
...

</P>
<DT><STRONG><A NAME="item_SSL_OP_TLS_BLOCK_PADDING_BUG">SSL_OP_TLS_BLOCK_PADDING_BUG</A></STRONG><DD>
<P>
...

</P>
<DT><STRONG><A NAME="item_SSL_OP_DONT_INSERT_EMPTY_FRAGMEN">SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS</A></STRONG><DD>
<P>
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.

</P>
<DT><STRONG><A NAME="item_SSL_OP_ALL">SSL_OP_ALL</A></STRONG><DD>
<P>
All of the above bug workarounds.

</P>
</DL>
<P>
It is usually safe to use <STRONG>SSL_OP_ALL</STRONG> to enable the bug workaround options if compatibility with somewhat broken
implementations is desired.

</P>
<P>
The following <STRONG>modifying</STRONG> options are available:

</P>
<DL>
<DT><STRONG><A NAME="item_SSL_OP_TLS_ROLLBACK_BUG">SSL_OP_TLS_ROLLBACK_BUG</A></STRONG><DD>
<P>
Disable version rollback attack detection.

</P>
<P>
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.)

</P>
<DT><STRONG><A NAME="item_SSL_OP_SINGLE_DH_USE">SSL_OP_SINGLE_DH_USE</A></STRONG><DD>
<P>
Always create a new key when using temporary/ephemeral DH parameters (see <A HREF="../ssl/SSL_CTX_set_tmp_dh_callback.html#">SSL_CTX_set_tmp_dh_callback(3)</A>). This option must be used to prevent small subgroup attacks, when the DH
parameters were not generated using ``strong'' primes (e.g. when using
DSA-parameters, see <A HREF="../apps/dhparam.html#">dhparam(1)</A>). If ``strong'' primes were used, it is not strictly necessary to generate
a new DH key during each handshake but it is also recommended.
<STRONG>SSL_OP_SINGLE_DH_USE</STRONG> should therefore be enabled whenever temporary/ephemeral DH parameters are
used.

</P>
<DT><STRONG><A NAME="item_SSL_OP_EPHEMERAL_RSA">SSL_OP_EPHEMERAL_RSA</A></STRONG><DD>
<P>
Always use ephemeral (temporary) RSA key when doing RSA operations (see <A HREF="../ssl/SSL_CTX_set_tmp_rsa_callback.html#">SSL_CTX_set_tmp_rsa_callback(3)</A>). According to the specifications this is only done, when a RSA key can
only be used for signature operations (namely under export ciphers with
restricted RSA keylength). By setting this option, ephemeral RSA keys are
always used. This option breaks compatibility with the SSL/TLS
specifications and may lead to interoperability problems with clients and
should therefore never be used. Ciphers with EDH (ephemeral Diffie-Hellman)
key exchange should be used instead.

</P>
<DT><STRONG><A NAME="item_SSL_OP_CIPHER_SERVER_PREFERENCE">SSL_OP_CIPHER_SERVER_PREFERENCE</A></STRONG><DD>
<P>
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 SSLv3/TLSv1 server will choose following its own
preferences. Because of the different protocol, for SSLv2 the server will
send its list of preferences to the client and the client chooses.

</P>
<DT><STRONG><A NAME="item_SSL_OP_PKCS1_CHECK_1">SSL_OP_PKCS1_CHECK_1</A></STRONG><DD>
<P>
...

</P>
<DT><STRONG><A NAME="item_SSL_OP_PKCS1_CHECK_2">SSL_OP_PKCS1_CHECK_2</A></STRONG><DD>
<P>
...

</P>
<DT><STRONG><A NAME="item_SSL_OP_NETSCAPE_CA_DN_BUG">SSL_OP_NETSCAPE_CA_DN_BUG</A></STRONG><DD>
<P>
If we accept a netscape connection, demand a client cert, have a
non-self-signed CA which does not have its CA in netscape, and the browser
has a cert, it will crash/hang. Works for 3.x and 4.xbeta 

</P>
<DT><STRONG><A NAME="item_SSL_OP_NETSCAPE_DEMO_CIPHER_CHAN">SSL_OP_NETSCAPE_DEMO_CIPHER_CHANGE_BUG</A></STRONG><DD>
<P>
...

</P>
<DT><STRONG><A NAME="item_SSL_OP_NO_SSLv2">SSL_OP_NO_SSLv2</A></STRONG><DD>
<P>
Do not use the SSLv2 protocol.

</P>
<DT><STRONG><A NAME="item_SSL_OP_NO_SSLv3">SSL_OP_NO_SSLv3</A></STRONG><DD>
<P>
Do not use the SSLv3 protocol.

</P>
<DT><STRONG><A NAME="item_SSL_OP_NO_TLSv1">SSL_OP_NO_TLSv1</A></STRONG><DD>
<P>
Do not use the TLSv1 protocol.

</P>
<DT><STRONG><A NAME="item_SSL_OP_NO_SESSION_RESUMPTION_ON_">SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION</A></STRONG><DD>
<P>
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.

</P>
<DT><STRONG><A NAME="item_SSL_OP_NO_TICKET">SSL_OP_NO_TICKET</A></STRONG><DD>
<P>
Normally clients and servers will, where possible, transparently make use
of RFC4507bis tickets for stateless session resumption.

</P>
<P>
If this option is set this functionality is disabled and tickets will not
be used by clients or servers.

</P>
</DL>
<P>
<HR>
<H1><A NAME="RETURN_VALUES">RETURN VALUES</A></H1>
<P>
<CODE>SSL_CTX_set_options()</CODE> and <CODE>SSL_set_options()</CODE>
return the new options bitmask after adding <STRONG>options</STRONG>.

</P>
<P>
<CODE>SSL_CTX_get_options()</CODE> and <CODE>SSL_get_options()</CODE>
return the current bitmask.

</P>
<P>
<HR>
<H1><A NAME="SEE_ALSO">SEE ALSO</A></H1>
<P>
<A HREF="../ssl/ssl.html#">ssl(3)</A>, <A HREF="../ssl/SSL_new.html#">SSL_new(3)</A>, <A HREF="../ssl/SSL_clear.html#">SSL_clear(3)</A>,
<A HREF="../ssl/SSL_CTX_set_tmp_dh_callback.html#">SSL_CTX_set_tmp_dh_callback(3)</A>,
<A HREF="../ssl/SSL_CTX_set_tmp_rsa_callback.html#">SSL_CTX_set_tmp_rsa_callback(3)</A>,
<A HREF="../apps/dhparam.html#">dhparam(1)</A>



</P>
<P>
<HR>
<H1><A NAME="HISTORY">HISTORY</A></H1>
<P>
<STRONG>SSL_OP_CIPHER_SERVER_PREFERENCE</STRONG> and
<STRONG>SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION</STRONG> have been added in OpenSSL 0.9.7.

</P>
<P>
<STRONG>SSL_OP_TLS_ROLLBACK_BUG</STRONG> has been added in OpenSSL 0.9.6 and was automatically enabled with <STRONG>SSL_OP_ALL</STRONG>. As of 0.9.7, it is no longer included in <STRONG>SSL_OP_ALL</STRONG>
and must be explicitly set.

</P>
<P>
<STRONG>SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS</STRONG> has been added in OpenSSL 0.9.6e. Versions up to OpenSSL 0.9.6c do not
include the countermeasure that can be disabled with this option (in
OpenSSL 0.9.6d, it was always enabled).

</P>
:}