Add initial security framework docs.

=head1 SYNOPSIS

B<openssl> B<ciphers>

[B<-s>]

[B<-v>]

[B<-V>]

[B<-ssl2>]

=over 4

=item B<-s>

Only list supported ciphers: those consistent with the security level. This

is the actual cipher list an application will support. If this option is

not used then ciphers excluded by the security level will still be listed.

=item B<-v>

Verbose option. List ciphers with a complete description of

list includes any ciphers already present they will be ignored: that is they

will not moved to the end of the list.

Additionally the cipher string B<@STRENGTH> can be used at any point to sort

the current cipher list in order of encryption algorithm key length.

The cipher string B<@STRENGTH> can be used at any point to sort the current

cipher list in order of encryption algorithm key length.

The cipher string B<@SECLEVEL=n> can be used at any point to set the security

level to B<n>.

=head1 CIPHER STRINGS

 openssl ciphers -v 'RSA:!COMPLEMENTOFALL'

Set security level to 2 and display all ciphers consistent with level 2:

 openssl ciphers -v 'ALL:@SECLEVEL=2'

=head1 SEE ALSO

L<s_client(1)|s_client(1)>, L<s_server(1)|s_server(1)>, L<ssl(3)|ssl(3)>

It should be noted, that inclusion of a cipher to be used into the list is

a necessary condition. On the client side, the inclusion into the list is

also sufficient. On the server side, additional restrictions apply. All ciphers

have additional requirements. ADH ciphers don't need a certificate, but

DH-parameters must have been set. All other ciphers need a corresponding

certificate and key.

also sufficient unless the security level excludes it. On the server side,

additional restrictions apply. All ciphers have additional requirements.

ADH ciphers don't need a certificate, but DH-parameters must have been set.

All other ciphers need a corresponding certificate and key.

A RSA cipher can only be chosen, when a RSA certificate is available.

RSA export ciphers with a keylength of 512 bits for the RSA key require

=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 <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);

=head1 DESCRIPTION

The functions SSL_CTX_set_security_level() and SSL_set_security_level() set

the security level to B<level>. 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<ctx> or B<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 B<ex> 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<Level 0>

Everything is permitted. This retains compatibility with previous versions of

OpenSSL.

=item B<Level 1>

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<Level 2>

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<Level 3>

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<Level 4>

Security level set to 192 bits of security. TLS versions below 1.2 are not

permitted.

=item B<Level 5>

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<ALL>

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