=pod =head1 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 =head1 SYNOPSIS #include 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); =head1 DESCRIPTION The functions SSL_CTX_set_security_level() and SSL_set_security_level() set the security level to B. If not set the libary 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 B or B. 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 B parameter of the callback. This value is passed to the callback verbatim and can be set to any convenient application specific value. =head1 DEFAULT CALLBACK BEHAVIOUR If an application doesn't set it's own security callback the default callback is used. It is intended to provide sane defaults. The meaning of each level is described below. =over 4 =item B Everything is permitted. This retains compatibility with previous versions of OpenSSL. =item B The security level set to 80 bits of security. Any parameters offering below 80 bits of security are excluded. As a result all export ciphersuites are prohibited. SSL version 2 is prohibited. Any ciphersuite using MD5 for the MAC is also prohibited. =item B Security level set to 112 bits of security. In addition to the level 1 exclusions any ciphersuite using RC4 is also prohibited. SSL version 3 is also not allowed. Compression is disabled. =item B Ssecurity level set to 128 bits of security. In addition to the level 2 exclusions any ciphersuite not offering forward secrecy are prohibited. TLS versions below 1.1 are not permitted. Session tickets are disabled. =item B Security level set to 192 bits of security. TLS versions below 1.2 are not permitted. =item B Security level set to 256 bits of security. =back =head1 APPLICATION DEFINED SECURITY CALLBACKS TBA =head1 NOTES The default security level can be configured when OpenSSL is compiled by setting B<-DOPENSSL_TLS_SECURITY_LEVEL=level>. If not set then 1 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 ciphersuite 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 ciphersuite is set to B then only ciphersuites consistent with the security level are permissible. See SP800-57 for how the security limits are related to individual algorithms. SHA1 is in widespread use in certificates but it only offers 80 bits of security. This is problematic as anything above level 1 will reject them. Some security levels require large key sizes for none-ECC public key algorithms. 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 ciphersuites 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 pameter 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 using SSL_CTX_use_certificate() at level 1. Applications which do not check the return values for errors will misbehave. =head1 SEE ALSO TBA =head1 HISTORY These functions were first added to OpenSSL 1.1.0 =cut