164 lines
6.5 KiB
Text
164 lines
6.5 KiB
Text
=pod
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=head1 NAME
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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
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=head1 SYNOPSIS
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#include <openssl/ssl.h>
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void SSL_CTX_set_security_level(SSL_CTX *ctx, int level);
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void SSL_set_security_level(SSL *s, int level);
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int SSL_CTX_get_security_level(const SSL_CTX *ctx);
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int SSL_get_security_level(const SSL *s);
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void SSL_CTX_set_security_callback(SSL_CTX *ctx,
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int (*cb)(SSL *s, SSL_CTX *ctx, int op, int bits, int nid,
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void *other, void *ex));
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void SSL_set_security_callback(SSL *s,
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int (*cb)(SSL *s, SSL_CTX *ctx, int op, int bits, int nid,
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void *other, void *ex));
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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);
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int (*SSL_get_security_callback(const SSL *s))(SSL *s, SSL_CTX *ctx, int op, int bits, int nid, void *other, void *ex);
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void SSL_CTX_set0_security_ex_data(SSL_CTX *ctx, void *ex);
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void SSL_set0_security_ex_data(SSL *s, void *ex);
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void *SSL_CTX_get0_security_ex_data(const SSL_CTX *ctx);
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void *SSL_get0_security_ex_data(const SSL *s);
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=head1 DESCRIPTION
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The functions SSL_CTX_set_security_level() and SSL_set_security_level() set
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the security level to B<level>. If not set the library default security level
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is used.
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The functions SSL_CTX_get_security_level() and SSL_get_security_level()
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retrieve the current security level.
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SSL_CTX_set_security_callback(), SSL_set_security_callback(),
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SSL_CTX_get_security_callback() and SSL_get_security_callback() get or set
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the security callback associated with B<ctx> or B<s>. If not set a default
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security callback is used. The meaning of the parameters and the behaviour
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of the default callbacks is described below.
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SSL_CTX_set0_security_ex_data(), SSL_set0_security_ex_data(),
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SSL_CTX_get0_security_ex_data() and SSL_get0_security_ex_data() set the
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extra data pointer passed to the B<ex> parameter of the callback. This
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value is passed to the callback verbatim and can be set to any convenient
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application specific value.
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=head1 DEFAULT CALLBACK BEHAVIOUR
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If an application doesn't set it's own security callback the default
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callback is used. It is intended to provide sane defaults. The meaning
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of each level is described below.
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=over 4
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=item B<Level 0>
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Everything is permitted. This retains compatibility with previous versions of
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OpenSSL.
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=item B<Level 1>
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The security level corresponds to a minimum of 80 bits of security. Any
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parameters offering below 80 bits of security are excluded. As a result RSA,
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DSA and DH keys shorter than 1024 bits and ECC keys shorter than 160 bits
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are prohibited. All export ciphersuites are prohibited since they all offer
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less than 80 bits of security. SSL version 2 is prohibited. Any ciphersuite
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using MD5 for the MAC is also prohibited.
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=item B<Level 2>
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Security level set to 112 bits of security. As a result RSA, DSA and DH keys
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shorter than 2048 bits and ECC keys shorter than 224 bits are prohibited.
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In addition to the level 1 exclusions any ciphersuite using RC4 is also
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prohibited. SSL version 3 is also not allowed. Compression is disabled.
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=item B<Level 3>
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Security level set to 128 bits of security. As a result RSA, DSA and DH keys
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shorter than 3072 bits and ECC keys shorter than 256 bits are prohibited.
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In addition to the level 2 exclusions ciphersuites not offering forward
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secrecy are prohibited. TLS versions below 1.1 are not permitted. Session
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tickets are disabled.
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=item B<Level 4>
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Security level set to 192 bits of security. As a result RSA, DSA and DH keys
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shorter than 7680 bits and ECC keys shorter than 384 bits are prohibited.
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Ciphersuites using SHA1 for the MAC are prohibited. TLS versions below 1.2 are
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not permitted.
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=item B<Level 5>
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Security level set to 256 bits of security. As a result RSA, DSA and DH keys
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shorter than 15360 bits and ECC keys shorter than 512 bits are prohibited.
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=back
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=head1 APPLICATION DEFINED SECURITY CALLBACKS
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TBA
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=head1 NOTES
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B<WARNING> at this time setting the security level higher than 1 for
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general internet use is likely to cause B<considerable> interoperability
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issues and is not recommended. This is because the B<SHA1> algorithm
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is very widely used in certificates and will be rejected at levels
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higher than 1 because it only offers 80 bits of security.
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The default security level can be configured when OpenSSL is compiled by
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setting B<-DOPENSSL_TLS_SECURITY_LEVEL=level>. If not set then 1 is used.
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The security framework disables or reject parameters inconsistent with the
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set security level. In the past this was difficult as applications had to set
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a number of distinct parameters (supported ciphers, supported curves supported
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signature algorithms) to achieve this end and some cases (DH parameter size
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for example) could not be checked at all.
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By setting an appropriate security level much of this complexity can be
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avoided.
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The bits of security limits affect all relevant parameters including
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ciphersuite encryption algorithms, supported ECC curves, supported
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signature algorithms, DH parameter sizes, certificate key sizes and
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signature algorithms. This limit applies no matter what other custom
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settings an application has set: so if the ciphersuite is set to B<ALL>
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then only ciphersuites consistent with the security level are permissible.
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See SP800-57 for how the security limits are related to individual
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algorithms.
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Some security levels require large key sizes for none-ECC public key
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algorithms which can severely degrade performance. For example 256 bits
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of security requires the use of RSA keys of at least 15360 bits in size.
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Some restrictions can be gracefully handled: for example ciphersuites
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offering insufficient security are not sent by the client and will not
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be selected by the server. Other restrictions such as the peer certificate
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key size or the DH parameter size will abort the handshake with a fatal
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alert.
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Attempts to set certificates or parameters with insufficient security are
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also blocked. For example trying to set a certificate using a 512 bit RSA
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key using SSL_CTX_use_certificate() at level 1. Applications which do not
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check the return values for errors will misbehave: for example it might
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appear that a certificate is not set at all because it had been rejected.
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=head1 SEE ALSO
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TBA
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=head1 HISTORY
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These functions were first added to OpenSSL 1.1.0
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=cut
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