SSL_CTX_set_options.pod revision 109998 
1=pod
2
3=head1 NAME
4
5SSL_CTX_set_options, SSL_set_options, SSL_CTX_get_options, SSL_get_options - manipulate SSL engine options
6
7=head1 SYNOPSIS
8
9 #include <openssl/ssl.h>
10
11 long SSL_CTX_set_options(SSL_CTX *ctx, long options);
12 long SSL_set_options(SSL *ssl, long options);
13
14 long SSL_CTX_get_options(SSL_CTX *ctx);
15 long SSL_get_options(SSL *ssl);
16
17=head1 DESCRIPTION
18
19SSL_CTX_set_options() adds the options set via bitmask in B<options> to B<ctx>.
20Options already set before are not cleared!
21
22SSL_set_options() adds the options set via bitmask in B<options> to B<ssl>.
23Options already set before are not cleared!
24
25SSL_CTX_get_options() returns the options set for B<ctx>.
26
27SSL_get_options() returns the options set for B<ssl>.
28
29=head1 NOTES
30
31The behaviour of the SSL library can be changed by setting several options.
32The options are coded as bitmasks and can be combined by a logical B<or>
33operation (|). Options can only be added but can never be reset.
34
35SSL_CTX_set_options() and SSL_set_options() affect the (external)
36protocol behaviour of the SSL library. The (internal) behaviour of
37the API can be changed by using the similar
38L<SSL_CTX_set_mode(3)|SSL_CTX_set_mode(3)> and SSL_set_mode() functions.
39
40During a handshake, the option settings of the SSL object are used. When
41a new SSL object is created from a context using SSL_new(), the current
42option setting is copied. Changes to B<ctx> do not affect already created
43SSL objects. SSL_clear() does not affect the settings.
44
45The following B<bug workaround> options are available:
46
47=over 4
48
49=item SSL_OP_MICROSOFT_SESS_ID_BUG
50
51www.microsoft.com - when talking SSLv2, if session-id reuse is
52performed, the session-id passed back in the server-finished message
53is different from the one decided upon.
54
55=item SSL_OP_NETSCAPE_CHALLENGE_BUG
56
57Netscape-Commerce/1.12, when talking SSLv2, accepts a 32 byte
58challenge but then appears to only use 16 bytes when generating the
59encryption keys.  Using 16 bytes is ok but it should be ok to use 32.
60According to the SSLv3 spec, one should use 32 bytes for the challenge
61when operating in SSLv2/v3 compatibility mode, but as mentioned above,
62this breaks this server so 16 bytes is the way to go.
63
64=item SSL_OP_NETSCAPE_REUSE_CIPHER_CHANGE_BUG
65
66ssl3.netscape.com:443, first a connection is established with RC4-MD5.
67If it is then resumed, we end up using DES-CBC3-SHA.  It should be
68RC4-MD5 according to 7.6.1.3, 'cipher_suite'.
69
70Netscape-Enterprise/2.01 (https://merchant.netscape.com) has this bug.
71It only really shows up when connecting via SSLv2/v3 then reconnecting
72via SSLv3. The cipher list changes....
73
74NEW INFORMATION.  Try connecting with a cipher list of just
75DES-CBC-SHA:RC4-MD5.  For some weird reason, each new connection uses
76RC4-MD5, but a re-connect tries to use DES-CBC-SHA.  So netscape, when
77doing a re-connect, always takes the first cipher in the cipher list.
78
79=item SSL_OP_SSLREF2_REUSE_CERT_TYPE_BUG
80
81...
82
83=item SSL_OP_MICROSOFT_BIG_SSLV3_BUFFER
84
85...
86
87=item SSL_OP_MSIE_SSLV2_RSA_PADDING
88
89...
90
91=item SSL_OP_SSLEAY_080_CLIENT_DH_BUG
92
93...
94
95=item SSL_OP_TLS_D5_BUG
96
97...
98
99=item SSL_OP_TLS_BLOCK_PADDING_BUG
100
101...
102
103=item SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS
104
105Disables a countermeasure against a SSL 3.0/TLS 1.0 protocol
106vulnerability affecting CBC ciphers, which cannot be handled by some
107broken SSL implementations.  This option has no effect for connections
108using other ciphers.
109
110=item SSL_OP_ALL
111
112All of the above bug workarounds.
113
114=back
115
116It is usually safe to use B<SSL_OP_ALL> to enable the bug workaround
117options if compatibility with somewhat broken implementations is
118desired.
119
120The following B<modifying> options are available:
121
122=over 4
123
124=item SSL_OP_TLS_ROLLBACK_BUG
125
126Disable version rollback attack detection.
127
128During the client key exchange, the client must send the same information
129about acceptable SSL/TLS protocol levels as during the first hello. Some
130clients violate this rule by adapting to the server's answer. (Example:
131the client sends a SSLv2 hello and accepts up to SSLv3.1=TLSv1, the server
132only understands up to SSLv3. In this case the client must still use the
133same SSLv3.1=TLSv1 announcement. Some clients step down to SSLv3 with respect
134to the server's answer and violate the version rollback protection.)
135
136=item SSL_OP_SINGLE_DH_USE
137
138Always create a new key when using temporary/ephemeral DH parameters
139(see L<SSL_CTX_set_tmp_dh_callback(3)|SSL_CTX_set_tmp_dh_callback(3)>).
140This option must be used to prevent small subgroup attacks, when
141the DH parameters were not generated using "strong" primes
142(e.g. when using DSA-parameters, see L<dhparam(1)|dhparam(1)>).
143If "strong" primes were used, it is not strictly necessary to generate
144a new DH key during each handshake but it is also recommended.
145B<SSL_OP_SINGLE_DH_USE> should therefore be enabled whenever
146temporary/ephemeral DH parameters are used.
147
148=item SSL_OP_EPHEMERAL_RSA
149
150Always use ephemeral (temporary) RSA key when doing RSA operations
151(see L<SSL_CTX_set_tmp_rsa_callback(3)|SSL_CTX_set_tmp_rsa_callback(3)>).
152According to the specifications this is only done, when a RSA key
153can only be used for signature operations (namely under export ciphers
154with restricted RSA keylength). By setting this option, ephemeral
155RSA keys are always used. This option breaks compatibility with the
156SSL/TLS specifications and may lead to interoperability problems with
157clients and should therefore never be used. Ciphers with EDH (ephemeral
158Diffie-Hellman) key exchange should be used instead.
159
160=item SSL_OP_CIPHER_SERVER_PREFERENCE
161
162When choosing a cipher, use the server's preferences instead of the client
163preferences. When not set, the SSL server will always follow the clients
164preferences. When set, the SSLv3/TLSv1 server will choose following its
165own preferences. Because of the different protocol, for SSLv2 the server
166will send his list of preferences to the client and the client chooses.
167
168=item SSL_OP_PKCS1_CHECK_1
169
170...
171
172=item SSL_OP_PKCS1_CHECK_2
173
174...
175
176=item SSL_OP_NETSCAPE_CA_DN_BUG
177
178If we accept a netscape connection, demand a client cert, have a
179non-self-sighed CA which does not have it's CA in netscape, and the
180browser has a cert, it will crash/hang.  Works for 3.x and 4.xbeta 
181
182=item SSL_OP_NETSCAPE_DEMO_CIPHER_CHANGE_BUG
183
184...
185
186=item SSL_OP_NO_SSLv2
187
188Do not use the SSLv2 protocol.
189
190=item SSL_OP_NO_SSLv3
191
192Do not use the SSLv3 protocol.
193
194=item SSL_OP_NO_TLSv1
195
196Do not use the TLSv1 protocol.
197
198=item SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION
199
200When performing renegotiation as a server, always start a new session
201(i.e., session resumption requests are only accepted in the initial
202handshake).  This option is not needed for clients.
203
204=back
205
206=head1 RETURN VALUES
207
208SSL_CTX_set_options() and SSL_set_options() return the new options bitmask
209after adding B<options>.
210
211SSL_CTX_get_options() and SSL_get_options() return the current bitmask.
212
213=head1 SEE ALSO
214
215L<ssl(3)|ssl(3)>, L<SSL_new(3)|SSL_new(3)>, L<SSL_clear(3)|SSL_clear(3)>,
216L<SSL_CTX_set_tmp_dh_callback(3)|SSL_CTX_set_tmp_dh_callback(3)>,
217L<SSL_CTX_set_tmp_rsa_callback(3)|SSL_CTX_set_tmp_rsa_callback(3)>,
218L<dhparam(1)|dhparam(1)>
219
220=head1 HISTORY
221
222B<SSL_OP_CIPHER_SERVER_PREFERENCE> and
223B<SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION> have been added in
224OpenSSL 0.9.7.
225
226B<SSL_OP_TLS_ROLLBACK_BUG> has been added in OpenSSL 0.9.6 and was automatically
227enabled with B<SSL_OP_ALL>. As of 0.9.7, it is no longer included in B<SSL_OP_ALL>
228and must be explicitly set.
229
230B<SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS> has been added in OpenSSL 0.9.6e.
231Versions up to OpenSSL 0.9.6c do not include the countermeasure that
232can be disabled with this option (in OpenSSL 0.9.6d, it was always
233enabled).
234
235=cut
236