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. Note that signatures using SHA1
81and MD5 are also forbidden at this level as they have less than 80 security
82bits.
83
84=item B<Level 2>
85
86Security level set to 112 bits of security. As a result RSA, DSA and DH keys
87shorter than 2048 bits and ECC keys shorter than 224 bits are prohibited.
88In addition to the level 1 exclusions any cipher suite using RC4 is also
89prohibited. SSL version 3 is also not allowed. Compression is disabled.
90
91=item B<Level 3>
92
93Security level set to 128 bits of security. As a result RSA, DSA and DH keys
94shorter than 3072 bits and ECC keys shorter than 256 bits are prohibited.
95In addition to the level 2 exclusions cipher suites not offering forward
96secrecy are prohibited. TLS versions below 1.1 are not permitted. Session
97tickets are disabled.
98
99=item B<Level 4>
100
101Security level set to 192 bits of security. As a result RSA, DSA and
102DH keys shorter than 7680 bits and ECC keys shorter than 384 bits are
103prohibited.  Cipher suites using SHA1 for the MAC are prohibited. TLS
104versions below 1.2 are not permitted.
105
106=item B<Level 5>
107
108Security level set to 256 bits of security. As a result RSA, DSA and DH keys
109shorter than 15360 bits and ECC keys shorter than 512 bits are prohibited.
110
111=back
112
113=head1 APPLICATION DEFINED SECURITY CALLBACKS
114
115I<Documentation to be provided.>
116
117=head1 NOTES
118
119The default security level can be configured when OpenSSL is compiled by
120setting B<-DOPENSSL_TLS_SECURITY_LEVEL=level>. If not set then 1 is used.
121
122The security framework disables or reject parameters inconsistent with the
123set security level. In the past this was difficult as applications had to set
124a number of distinct parameters (supported ciphers, supported curves supported
125signature algorithms) to achieve this end and some cases (DH parameter size
126for example) could not be checked at all.
127
128By setting an appropriate security level much of this complexity can be
129avoided.
130
131The bits of security limits affect all relevant parameters including
132cipher suite encryption algorithms, supported ECC curves, supported
133signature algorithms, DH parameter sizes, certificate key sizes and
134signature algorithms. This limit applies no matter what other custom
135settings an application has set: so if the cipher suite is set to B<ALL>
136then only cipher suites consistent with the security level are permissible.
137
138See SP800-57 for how the security limits are related to individual
139algorithms.
140
141Some security levels require large key sizes for non-ECC public key
142algorithms which can severely degrade performance. For example 256 bits
143of security requires the use of RSA keys of at least 15360 bits in size.
144
145Some restrictions can be gracefully handled: for example cipher suites
146offering insufficient security are not sent by the client and will not
147be selected by the server. Other restrictions such as the peer certificate
148key size or the DH parameter size will abort the handshake with a fatal
149alert.
150
151Attempts to set certificates or parameters with insufficient security are
152also blocked. For example trying to set a certificate using a 512 bit RSA key
153or a certificate with a signature with SHA1 digest at level 1 using
154SSL_CTX_use_certificate(). Applications which do not check the return values
155for errors will misbehave: for example it might appear that a certificate is
156not set at all because it had been rejected.
157
158=head1 RETURN VALUES
159
160SSL_CTX_set_security_level() and SSL_set_security_level() do not return values.
161
162SSL_CTX_get_security_level() and SSL_get_security_level() return a integer that
163represents the security level with B<SSL_CTX> or B<SSL>, respectively.
164
165SSL_CTX_set_security_callback() and SSL_set_security_callback() do not return
166values.
167
168SSL_CTX_get_security_callback() and SSL_get_security_callback() return the pointer
169to the security callback or NULL if the callback is not set.
170
171SSL_CTX_get0_security_ex_data() and SSL_get0_security_ex_data() return the extra
172data pointer or NULL if the ex data is not set.
173
174=head1 SEE ALSO
175
176L<ssl(7)>
177
178=head1 HISTORY
179
180These functions were added in OpenSSL 1.1.0.
181
182=head1 COPYRIGHT
183
184Copyright 2014-2021 The OpenSSL Project Authors. All Rights Reserved.
185
186Licensed under the Apache License 2.0 (the "License").  You may not use
187this file except in compliance with the License.  You can obtain a copy
188in the file LICENSE in the source distribution or at
189L<https://www.openssl.org/source/license.html>.
190
191=cut
192