1=pod
2
3=head1 NAME
4
5SSL_CTX_set_security_level, SSL_set_security_level, SSL_CTX_get_security_level, SSL_get_security_level, SSL_CTX_set_security_callback, SSL_set_security_callback, SSL_CTX_get_security_callback, SSL_get_security_callback, SSL_CTX_set0_security_ex_data, SSL_set0_security_ex_data, SSL_CTX_get0_security_ex_data, SSL_get0_security_ex_data - SSL/TLS security framework
6
7=head1 SYNOPSIS
8
9 #include <openssl/ssl.h>
10
11 void SSL_CTX_set_security_level(SSL_CTX *ctx, int level);
12 void SSL_set_security_level(SSL *s, int level);
13
14 int SSL_CTX_get_security_level(const SSL_CTX *ctx);
15 int SSL_get_security_level(const SSL *s);
16
17 void SSL_CTX_set_security_callback(SSL_CTX *ctx,
18                                    int (*cb)(SSL *s, SSL_CTX *ctx, int op,
19                                              int bits, int nid,
20                                              void *other, void *ex));
21
22 void SSL_set_security_callback(SSL *s, int (*cb)(SSL *s, SSL_CTX *ctx, int op,
23                                                  int bits, int nid,
24                                                  void *other, void *ex));
25
26 int (*SSL_CTX_get_security_callback(const SSL_CTX *ctx))(SSL *s, SSL_CTX *ctx, int op,
27                                                          int bits, int nid, void *other,
28                                                          void *ex);
29 int (*SSL_get_security_callback(const SSL *s))(SSL *s, SSL_CTX *ctx, int op,
30                                                int bits, int nid, void *other,
31                                                void *ex);
32
33 void SSL_CTX_set0_security_ex_data(SSL_CTX *ctx, void *ex);
34 void SSL_set0_security_ex_data(SSL *s, void *ex);
35
36 void *SSL_CTX_get0_security_ex_data(const SSL_CTX *ctx);
37 void *SSL_get0_security_ex_data(const SSL *s);
38
39=head1 DESCRIPTION
40
41The functions SSL_CTX_set_security_level() and SSL_set_security_level() set
42the security level to B<level>. If not set the library default security level
43is used.
44
45The functions SSL_CTX_get_security_level() and SSL_get_security_level()
46retrieve the current security level.
47
48SSL_CTX_set_security_callback(), SSL_set_security_callback(),
49SSL_CTX_get_security_callback() and SSL_get_security_callback() get or set
50the security callback associated with B<ctx> or B<s>. If not set a default
51security callback is used. The meaning of the parameters and the behaviour
52of the default callbacks is described below.
53
54SSL_CTX_set0_security_ex_data(), SSL_set0_security_ex_data(),
55SSL_CTX_get0_security_ex_data() and SSL_get0_security_ex_data() set the
56extra data pointer passed to the B<ex> parameter of the callback. This
57value is passed to the callback verbatim and can be set to any convenient
58application specific value.
59
60=head1 DEFAULT CALLBACK BEHAVIOUR
61
62If an application doesn't set its own security callback the default
63callback is used. It is intended to provide sane defaults. The meaning
64of each level is described below.
65
66=over 4
67
68=item B<Level 0>
69
70Everything is permitted. This retains compatibility with previous versions of
71OpenSSL.
72
73=item B<Level 1>
74
75The security level corresponds to a minimum of 80 bits of security. Any
76parameters offering below 80 bits of security are excluded. As a result RSA,
77DSA and DH keys shorter than 1024 bits and ECC keys shorter than 160 bits
78are prohibited. Any cipher suite using MD5 for the MAC is also prohibited. Any
79cipher suites using CCM with a 64 bit authentication tag are prohibited. Note
80that signatures using SHA1 and MD5 are also forbidden at this level as they
81have less than 80 security bits.
82
83=item B<Level 2>
84
85Security level set to 112 bits of security. As a result RSA, DSA and DH keys
86shorter than 2048 bits and ECC keys shorter than 224 bits are prohibited.
87In addition to the level 1 exclusions any cipher suite using RC4 is also
88prohibited. SSL version 3 is also not allowed. Compression is disabled.
89
90=item B<Level 3>
91
92Security level set to 128 bits of security. As a result RSA, DSA and DH keys
93shorter than 3072 bits and ECC keys shorter than 256 bits are prohibited.
94In addition to the level 2 exclusions cipher suites not offering forward
95secrecy are prohibited. TLS versions below 1.1 are not permitted. Session
96tickets are disabled.
97
98=item B<Level 4>
99
100Security level set to 192 bits of security. As a result RSA, DSA and
101DH keys shorter than 7680 bits and ECC keys shorter than 384 bits are
102prohibited.  Cipher suites using SHA1 for the MAC are prohibited. TLS
103versions below 1.2 are not permitted.
104
105=item B<Level 5>
106
107Security level set to 256 bits of security. As a result RSA, DSA and DH keys
108shorter than 15360 bits and ECC keys shorter than 512 bits are prohibited.
109
110=back
111
112=head1 APPLICATION DEFINED SECURITY CALLBACKS
113
114I<Documentation to be provided.>
115
116=head1 NOTES
117
118The default security level can be configured when OpenSSL is compiled by
119setting B<-DOPENSSL_TLS_SECURITY_LEVEL=level>. If not set then 2 is used.
120
121The security framework disables or reject parameters inconsistent with the
122set security level. In the past this was difficult as applications had to set
123a number of distinct parameters (supported ciphers, supported curves supported
124signature algorithms) to achieve this end and some cases (DH parameter size
125for example) could not be checked at all.
126
127By setting an appropriate security level much of this complexity can be
128avoided.
129
130The bits of security limits affect all relevant parameters including
131cipher suite encryption algorithms, supported ECC curves, supported
132signature algorithms, DH parameter sizes, certificate key sizes and
133signature algorithms. This limit applies no matter what other custom
134settings an application has set: so if the cipher suite is set to B<ALL>
135then only cipher suites consistent with the security level are permissible.
136
137See SP800-57 for how the security limits are related to individual
138algorithms.
139
140Some security levels require large key sizes for non-ECC public key
141algorithms which can severely degrade performance. For example 256 bits
142of security requires the use of RSA keys of at least 15360 bits in size.
143
144Some restrictions can be gracefully handled: for example cipher suites
145offering insufficient security are not sent by the client and will not
146be selected by the server. Other restrictions such as the peer certificate
147key size or the DH parameter size will abort the handshake with a fatal
148alert.
149
150Attempts to set certificates or parameters with insufficient security are
151also blocked. For example trying to set a certificate using a 512 bit RSA key
152or a certificate with a signature with SHA1 digest at level 1 using
153SSL_CTX_use_certificate(). Applications which do not check the return values
154for errors will misbehave: for example it might appear that a certificate is
155not set at all because it had been rejected.
156
157=head1 RETURN VALUES
158
159SSL_CTX_set_security_level() and SSL_set_security_level() do not return values.
160
161SSL_CTX_get_security_level() and SSL_get_security_level() return a integer that
162represents the security level with B<SSL_CTX> or B<SSL>, respectively.
163
164SSL_CTX_set_security_callback() and SSL_set_security_callback() do not return
165values.
166
167SSL_CTX_get_security_callback() and SSL_get_security_callback() return the pointer
168to the security callback or NULL if the callback is not set.
169
170SSL_CTX_get0_security_ex_data() and SSL_get0_security_ex_data() return the extra
171data pointer or NULL if the ex data is not set.
172
173=head1 SEE ALSO
174
175L<ssl(7)>
176
177=head1 HISTORY
178
179These functions were added in OpenSSL 1.1.0.
180
181=head1 COPYRIGHT
182
183Copyright 2014-2020 The OpenSSL Project Authors. All Rights Reserved.
184
185Licensed under the Apache License 2.0 (the "License").  You may not use
186this file except in compliance with the License.  You can obtain a copy
187in the file LICENSE in the source distribution or at
188L<https://www.openssl.org/source/license.html>.
189
190=cut
191