1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
|
=pod
=head1 NAME
SSL_CTX_set_options, SSL_set_options, SSL_CTX_get_options, SSL_get_options - manipulate SSL engine options
=head1 SYNOPSIS
#include <openssl/ssl.h>
long SSL_CTX_set_options(SSL_CTX *ctx, long options);
long SSL_set_options(SSL *ssl, long options);
long SSL_CTX_get_options(SSL_CTX *ctx);
long SSL_get_options(SSL *ssl);
=head1 DESCRIPTION
SSL_CTX_set_options() adds the options set via bitmask in B<options> to B<ctx>.
Options already set before are not cleared!
SSL_set_options() adds the options set via bitmask in B<options> to B<ssl>.
Options already set before are not cleared!
SSL_CTX_get_options() returns the options set for B<ctx>.
SSL_get_options() returns the options set for B<ssl>.
=head1 NOTES
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 B<or>
operation (|). Options can only be added but can never be reset.
SSL_CTX_set_options() 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
L<SSL_CTX_set_mode(3)|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 B<ctx> do not affect already created
SSL objects. SSL_clear() does not affect the settings.
The following B<bug workaround> options are available:
=over 4
=item SSL_OP_MICROSOFT_SESS_ID_BUG
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.
=item SSL_OP_NETSCAPE_CHALLENGE_BUG
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.
=item SSL_OP_NETSCAPE_REUSE_CIPHER_CHANGE_BUG
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'.
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....
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.
=item SSL_OP_SSLREF2_REUSE_CERT_TYPE_BUG
...
=item SSL_OP_MICROSOFT_BIG_SSLV3_BUFFER
...
=item SSL_OP_MSIE_SSLV2_RSA_PADDING
As of OpenSSL 0.9.7h and 0.9.8a, this option has no effect.
=item SSL_OP_SSLEAY_080_CLIENT_DH_BUG
...
=item SSL_OP_TLS_D5_BUG
...
=item SSL_OP_TLS_BLOCK_PADDING_BUG
...
=item 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.
=item SSL_OP_ALL
All of the above bug workarounds.
=back
It is usually safe to use B<SSL_OP_ALL> to enable the bug workaround
options if compatibility with somewhat broken implementations is
desired.
The following B<modifying> options are available:
=over 4
=item 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.)
=item SSL_OP_SINGLE_DH_USE
Always create a new key when using temporary/ephemeral DH parameters
(see L<SSL_CTX_set_tmp_dh_callback(3)|SSL_CTX_set_tmp_dh_callback(3)>).
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 L<dhparam(1)|dhparam(1)>).
If "strong" primes were used, it is not strictly necessary to generate
a new DH key during each handshake but it is also recommended.
B<SSL_OP_SINGLE_DH_USE> should therefore be enabled whenever
temporary/ephemeral DH parameters are used.
=item SSL_OP_EPHEMERAL_RSA
Always use ephemeral (temporary) RSA key when doing RSA operations
(see L<SSL_CTX_set_tmp_rsa_callback(3)|SSL_CTX_set_tmp_rsa_callback(3)>).
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.
=item 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 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.
=item SSL_OP_PKCS1_CHECK_1
...
=item SSL_OP_PKCS1_CHECK_2
...
=item SSL_OP_NETSCAPE_CA_DN_BUG
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
=item SSL_OP_NETSCAPE_DEMO_CIPHER_CHANGE_BUG
...
=item SSL_OP_NO_SSLv2
Do not use the SSLv2 protocol.
=item SSL_OP_NO_SSLv3
Do not use the SSLv3 protocol.
=item SSL_OP_NO_TLSv1
Do not use the TLSv1 protocol.
=item 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.
=item SSL_OP_NO_TICKET
Normally clients and servers will, where possible, transparently make use
of RFC4507bis tickets for stateless session resumption if extension support
is explicitly set when OpenSSL is compiled.
If this option is set this functionality is disabled and tickets will
not be used by clients or servers.
=back
=head1 RETURN VALUES
SSL_CTX_set_options() and SSL_set_options() return the new options bitmask
after adding B<options>.
SSL_CTX_get_options() and SSL_get_options() return the current bitmask.
=head1 SEE ALSO
L<ssl(3)|ssl(3)>, L<SSL_new(3)|SSL_new(3)>, L<SSL_clear(3)|SSL_clear(3)>,
L<SSL_CTX_set_tmp_dh_callback(3)|SSL_CTX_set_tmp_dh_callback(3)>,
L<SSL_CTX_set_tmp_rsa_callback(3)|SSL_CTX_set_tmp_rsa_callback(3)>,
L<dhparam(1)|dhparam(1)>
=head1 HISTORY
B<SSL_OP_CIPHER_SERVER_PREFERENCE> and
B<SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION> have been added in
OpenSSL 0.9.7.
B<SSL_OP_TLS_ROLLBACK_BUG> has been added in OpenSSL 0.9.6 and was automatically
enabled with B<SSL_OP_ALL>. As of 0.9.7, it is no longer included in B<SSL_OP_ALL>
and must be explicitly set.
B<SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS> 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).
=cut
|
