Provided by: libssl-doc_3.4.1-1ubuntu3_all bug

NAME

       SSL_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

SYNOPSIS

        #include <openssl/ssl.h>

        void SSL_CTX_set_security_level(SSL_CTX *ctx, int level);
        void SSL_set_security_level(SSL *s, int level);

        int SSL_CTX_get_security_level(const SSL_CTX *ctx);
        int SSL_get_security_level(const SSL *s);

        void SSL_CTX_set_security_callback(SSL_CTX *ctx,
                                           int (*cb)(SSL *s, SSL_CTX *ctx, int op,
                                                     int bits, int nid,
                                                     void *other, void *ex));

        void SSL_set_security_callback(SSL *s, int (*cb)(SSL *s, SSL_CTX *ctx, int op,
                                                         int bits, int nid,
                                                         void *other, void *ex));

        int (*SSL_CTX_get_security_callback(const SSL_CTX *ctx))(SSL *s, SSL_CTX *ctx, int op,
                                                                 int bits, int nid, void *other,
                                                                 void *ex);
        int (*SSL_get_security_callback(const SSL *s))(SSL *s, SSL_CTX *ctx, int op,
                                                       int bits, int nid, void *other,
                                                       void *ex);

        void SSL_CTX_set0_security_ex_data(SSL_CTX *ctx, void *ex);
        void SSL_set0_security_ex_data(SSL *s, void *ex);

        void *SSL_CTX_get0_security_ex_data(const SSL_CTX *ctx);
        void *SSL_get0_security_ex_data(const SSL *s);

DESCRIPTION

       The functions SSL_CTX_set_security_level() and SSL_set_security_level() set the security level to level.
       If not set the library default security level is used.

       The functions SSL_CTX_get_security_level() and SSL_get_security_level() retrieve the current security
       level.

       SSL_CTX_set_security_callback(), SSL_set_security_callback(), SSL_CTX_get_security_callback() and
       SSL_get_security_callback() get or set the security callback associated with ctx or s. If not set a
       default security callback is used. The meaning of the parameters and the behaviour of the default
       callbacks is described below.

       SSL_CTX_set0_security_ex_data(), SSL_set0_security_ex_data(), SSL_CTX_get0_security_ex_data() and
       SSL_get0_security_ex_data() set the extra data pointer passed to the ex parameter of the callback. This
       value is passed to the callback verbatim and can be set to any convenient application specific value.

DEFAULT CALLBACK BEHAVIOUR

       If an application doesn't set its own security callback the default callback is used. It is intended to
       provide sane defaults. The meaning of each level is described below.

       Level 0
           Everything is permitted. This retains compatibility with previous versions of OpenSSL.

       Level 1
           The  security level corresponds to a minimum of 80 bits of security. Any parameters offering below 80
           bits of security are excluded. As a result RSA, DSA and DH keys shorter than 1024 bits and  ECC  keys
           shorter  than 160 bits are prohibited. Any cipher suite using MD5 for the MAC is also prohibited. Any
           cipher suites using CCM with a 64 bit authentication tag are prohibited. Note that  signatures  using
           SHA1  and MD5 are also forbidden at this level as they have less than 80 security bits. Additionally,
           SSLv3, TLS 1.0, TLS 1.1 and DTLS 1.0 are all disabled at this level.

       Level 2
           Security level set to 112 bits of security. As a result RSA, DSA and DH keys shorter than  2048  bits
           and  ECC keys shorter than 224 bits are prohibited.  In addition to the level 1 exclusions any cipher
           suite using RC4 is also prohibited. Compression is disabled.

       Level 3
           Security level set to 128 bits of security. As a result RSA, DSA and DH keys shorter than  3072  bits
           and  ECC  keys  shorter  than  256 bits are prohibited.  In addition to the level 2 exclusions cipher
           suites not offering forward secrecy are prohibited. Session tickets are disabled.

       Level 4
           Security level set to 192 bits of security. As a result RSA, DSA and DH keys shorter than  7680  bits
           and  ECC  keys  shorter  than  384  bits  are  prohibited.   Cipher suites using SHA1 for the MAC are
           prohibited.

       Level 5
           Security level set to 256 bits of security. As a result RSA, DSA and DH keys shorter than 15360  bits
           and ECC keys shorter than 512 bits are prohibited.

APPLICATION DEFINED SECURITY CALLBACKS

       Documentation to be provided.

NOTES

       The    default   security   level   can   be   configured   when   OpenSSL   is   compiled   by   setting
       -DOPENSSL_TLS_SECURITY_LEVEL=level. If not set then 2 is used.

       The security framework disables or reject parameters inconsistent with the set  security  level.  In  the
       past  this  was  difficult as applications had to set a number of distinct parameters (supported ciphers,
       supported curves supported signature algorithms) to achieve this end and some cases  (DH  parameter  size
       for example) could not be checked at all.

       By setting an appropriate security level much of this complexity can be avoided.

       The  bits of security limits affect all relevant parameters including cipher suite encryption algorithms,
       supported ECC curves, supported signature algorithms, DH  parameter  sizes,  certificate  key  sizes  and
       signature  algorithms. This limit applies no matter what other custom settings an application has set: so
       if the cipher suite is set to ALL then  only  cipher  suites  consistent  with  the  security  level  are
       permissible.

       See SP800-57 for how the security limits are related to individual algorithms.

       Some security levels require large key sizes for non-ECC public key algorithms which can severely degrade
       performance.  For  example  256  bits  of security requires the use of RSA keys of at least 15360 bits in
       size.

       Some restrictions can be gracefully handled: for example cipher suites offering insufficient security are
       not sent by the client and will not be selected by the  server.  Other  restrictions  such  as  the  peer
       certificate key size or the DH parameter size will abort the handshake with a fatal alert.

       Attempts  to  set  certificates  or  parameters  with insufficient security are also blocked. For example
       trying to set a certificate using a 512 bit RSA key or a certificate with a signature with SHA1 digest at
       level 1 using SSL_CTX_use_certificate(). Applications which do not check the  return  values  for  errors
       will  misbehave:  for  example  it  might appear that a certificate is not set at all because it had been
       rejected.

RETURN VALUES

       SSL_CTX_set_security_level() and SSL_set_security_level() do not return values.

       SSL_CTX_get_security_level() and SSL_get_security_level() return a integer that represents  the  security
       level with SSL_CTX or SSL, respectively.

       SSL_CTX_set_security_callback() and SSL_set_security_callback() do not return values.

       SSL_CTX_get_security_callback()  and  SSL_get_security_callback()  return  the  pointer  to  the security
       callback or NULL if the callback is not set.

       SSL_CTX_get0_security_ex_data() and SSL_get0_security_ex_data() return the extra data pointer or NULL  if
       the ex data is not set.

SEE ALSO

       ssl(7)

HISTORY

       These functions were added in OpenSSL 1.1.0.

COPYRIGHT

       Copyright 2014-2020 The OpenSSL Project Authors. All Rights Reserved.

       Licensed  under  the  Apache License 2.0 (the "License").  You may not use this file except in compliance
       with the License.  You can obtain  a  copy  in  the  file  LICENSE  in  the  source  distribution  or  at
       <https://www.openssl.org/source/license.html>.

3.4.1                                              2025-04-03                   SSL_CTX_SET_SECURITY_LEVEL(3SSL)