xref: /freebsd/crypto/openssl/doc/man3/SSL_CTX_set_security_level.pod (revision f6a3b357e9be4c6423c85eff9a847163a0d307c8)
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. All export cipher suites are prohibited since they all offer
79less than 80 bits of security. SSL version 2 is prohibited. Any cipher suite
80using MD5 for the MAC is also prohibited.
81
82=item B<Level 2>
83
84Security level set to 112 bits of security. As a result RSA, DSA and DH keys
85shorter than 2048 bits and ECC keys shorter than 224 bits are prohibited.
86In addition to the level 1 exclusions any cipher suite using RC4 is also
87prohibited. SSL version 3 is also not allowed. Compression is disabled.
88
89=item B<Level 3>
90
91Security level set to 128 bits of security. As a result RSA, DSA and DH keys
92shorter than 3072 bits and ECC keys shorter than 256 bits are prohibited.
93In addition to the level 2 exclusions cipher suites not offering forward
94secrecy are prohibited. TLS versions below 1.1 are not permitted. Session
95tickets are disabled.
96
97=item B<Level 4>
98
99Security level set to 192 bits of security. As a result RSA, DSA and
100DH keys shorter than 7680 bits and ECC keys shorter than 384 bits are
101prohibited.  Cipher suites using SHA1 for the MAC are prohibited. TLS
102versions below 1.2 are not permitted.
103
104=item B<Level 5>
105
106Security level set to 256 bits of security. As a result RSA, DSA and DH keys
107shorter than 15360 bits and ECC keys shorter than 512 bits are prohibited.
108
109=back
110
111=head1 APPLICATION DEFINED SECURITY CALLBACKS
112
113I<Documentation to be provided.>
114
115=head1 NOTES
116
117B<WARNING> at this time setting the security level higher than 1 for
118general internet use is likely to cause B<considerable> interoperability
119issues and is not recommended. This is because the B<SHA1> algorithm
120is very widely used in certificates and will be rejected at levels
121higher than 1 because it only offers 80 bits of security.
122
123The default security level can be configured when OpenSSL is compiled by
124setting B<-DOPENSSL_TLS_SECURITY_LEVEL=level>. If not set then 1 is used.
125
126The security framework disables or reject parameters inconsistent with the
127set security level. In the past this was difficult as applications had to set
128a number of distinct parameters (supported ciphers, supported curves supported
129signature algorithms) to achieve this end and some cases (DH parameter size
130for example) could not be checked at all.
131
132By setting an appropriate security level much of this complexity can be
133avoided.
134
135The bits of security limits affect all relevant parameters including
136cipher suite encryption algorithms, supported ECC curves, supported
137signature algorithms, DH parameter sizes, certificate key sizes and
138signature algorithms. This limit applies no matter what other custom
139settings an application has set: so if the cipher suite is set to B<ALL>
140then only cipher suites consistent with the security level are permissible.
141
142See SP800-57 for how the security limits are related to individual
143algorithms.
144
145Some security levels require large key sizes for non-ECC public key
146algorithms which can severely degrade performance. For example 256 bits
147of security requires the use of RSA keys of at least 15360 bits in size.
148
149Some restrictions can be gracefully handled: for example cipher suites
150offering insufficient security are not sent by the client and will not
151be selected by the server. Other restrictions such as the peer certificate
152key size or the DH parameter size will abort the handshake with a fatal
153alert.
154
155Attempts to set certificates or parameters with insufficient security are
156also blocked. For example trying to set a certificate using a 512 bit RSA
157key using SSL_CTX_use_certificate() at level 1. Applications which do not
158check the return values for errors will misbehave: for example it might
159appear that a certificate is not set at all because it had been rejected.
160
161=head1 RETURN VALUES
162
163SSL_CTX_set_security_level() and SSL_set_security_level() do not return values.
164
165SSL_CTX_get_security_level() and SSL_get_security_level() return a integer that
166represents the security level with B<SSL_CTX> or B<SSL>, respectively.
167
168SSL_CTX_set_security_callback() and SSL_set_security_callback() do not return
169values.
170
171SSL_CTX_get_security_callback() and SSL_get_security_callback() return the pointer
172to the security callback or NULL if the callback is not set.
173
174SSL_CTX_get0_security_ex_data() and SSL_get0_security_ex_data() return the extra
175data pointer or NULL if the ex data is not set.
176
177=head1 HISTORY
178
179These functions were added in OpenSSL 1.1.0.
180
181=head1 COPYRIGHT
182
183Copyright 2014-2018 The OpenSSL Project Authors. All Rights Reserved.
184
185Licensed under the OpenSSL license (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