SSL_CTX_set_options.pod revision 89837 
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_modes(3)|SSL_CTX_set_modes(3)> and SSL_set_modes() 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_TLS_ROLLBACK_BUG
104
105Disable version rollback attack detection.
106
107During the client key exchange, the client must send the same information
108about acceptable SSL/TLS protocol levels as during the first hello. Some
109clients violate this rule by adapting to the server's answer. (Example:
110the client sends a SSLv2 hello and accepts up to SSLv3.1=TLSv1, the server
111only understands up to SSLv3. In this case the client must still use the
112same SSLv3.1=TLSv1 announcement. Some clients step down to SSLv3 with respect
113to the server's answer and violate the version rollback protection.)
114
115=item SSL_OP_ALL
116
117All of the above bug workarounds.
118
119=back
120
121It is save and recommended to use SSL_OP_ALL to enable the bug workaround
122options.
123
124The following B<modifying> options are available:
125
126=over 4
127
128=item SSL_OP_SINGLE_DH_USE
129
130Always create a new key when using temporary/ephemeral DH parameters
131(see L<SSL_CTX_set_tmp_dh_callback(3)|SSL_CTX_set_tmp_dh_callback(3)>).
132This option must be used to prevent small subgroup attacks, when
133the DH parameters were not generated using "strong" primes
134(e.g. when using DSA-parameters, see L<dhparam(1)|dhparam(1)>).
135If "strong" primes were used, it is not strictly necessary to generate
136a new DH key during each handshake but it is also recommended.
137SSL_OP_SINGLE_DH_USE should therefore be enabled whenever
138temporary/ephemeral DH parameters are used.
139
140=item SSL_OP_EPHEMERAL_RSA
141
142Always use ephemeral (temporary) RSA key when doing RSA operations
143(see L<SSL_CTX_set_tmp_rsa_callback(3)|SSL_CTX_set_tmp_rsa_callback(3)>).
144According to the specifications this is only done, when a RSA key
145can only be used for signature operations (namely under export ciphers
146with restricted RSA keylength). By setting this option, ephemeral
147RSA keys are always used. This option breaks compatibility with the
148SSL/TLS specifications and may lead to interoperability problems with
149clients and should therefore never be used. Ciphers with EDH (ephemeral
150Diffie-Hellman) key exchange should be used instead.
151
152=item SSL_OP_PKCS1_CHECK_1
153
154...
155
156=item SSL_OP_PKCS1_CHECK_2
157
158...
159
160=item SSL_OP_NETSCAPE_CA_DN_BUG
161
162If we accept a netscape connection, demand a client cert, have a
163non-self-sighed CA which does not have it's CA in netscape, and the
164browser has a cert, it will crash/hang.  Works for 3.x and 4.xbeta 
165
166=item SSL_OP_NETSCAPE_DEMO_CIPHER_CHANGE_BUG
167
168...
169
170=item SSL_OP_NO_SSLv2
171
172Do not use the SSLv2 protocol.
173
174=item SSL_OP_NO_SSLv3
175
176Do not use the SSLv3 protocol.
177
178=item SSL_OP_NO_TLSv1
179
180Do not use the TLSv1 protocol.
181
182=back
183
184=head1 RETURN VALUES
185
186SSL_CTX_set_options() and SSL_set_options() return the new options bitmask
187after adding B<options>.
188
189SSL_CTX_get_options() and SSL_get_options() return the current bitmask.
190
191=head1 SEE ALSO
192
193L<ssl(3)|ssl(3)>, L<SSL_new(3)|SSL_new(3)>, L<SSL_clear(3)|SSL_clear(3)>,
194L<SSL_CTX_set_tmp_dh_callback(3)|SSL_CTX_set_tmp_dh_callback(3)>,
195L<SSL_CTX_set_tmp_rsa_callback(3)|SSL_CTX_set_tmp_rsa_callback(3)>,
196L<dhparam(1)|dhparam(1)>
197
198=head1 HISTORY
199
200SSL_OP_TLS_ROLLBACK_BUG has been added in OpenSSL 0.9.6.
201
202=cut
203