More doc fixes.

[B<-pass arg>]

[B<-CApath directory>]

[B<-CAfile filename>]

[B<-trusted_first>]

[B<-attime timestamp>]

[B<-check_ss_sig>]

[B<-crl_check>]

[B<-policy_check>]

[B<-policy_print>]

[B<-purpose purpose>]

[B<-trusted_first>]

[B<-use_deltas>]

[B<-verify_depth num>]

[B<-x509_strict>]

B<explicit_policy>, B<-ignore_critical>, B<-inhibit_any>,

B<-inhibit_map>, B<-issuer_checks>, B<-policy>,

B<-policy_check>, B<-policy_print>, B<-purpose>,

B<-trusted_first>, B<-use_deltas>,

B<-verify_depth>,

B<-x509_strict>

B<-use_deltas>, B<-verify_depth>, B<-x509_strict>

Set various certificate chain valiadition options. See the

L<B<verify>|verify(1)> manual page for details.

[B<-policy_check>]

[B<-policy_print>]

[B<-purpose purpose>]

[B<-trusted_first>]

[B<-untrusted file>]

[B<-use_deltas>]

[B<-verbose>]

B<smimesign>, B<smimeencrypt>. See the B<VERIFY OPERATION> section for more

information.

=item B<-trusted_first>

Use certificates in CA file or CA directory before certificates in untrusted

file when building the trust chain to verify certificates.

This is mainly useful in environments with Bridge CA or Cross-Certified CAs.

=item B<-untrusted file>

A file of untrusted certificates. The file should contain multiple certificates

=pod

=head1 NAME

SSL_CTX_set_cert_cb, SSL_set_cert_cb - handle certificate callback function

=head1 SYNOPSIS

 #include <openssl/ssl.h>

 void SSL_CTX_set_cert_cb(SSL_CTX *c, int (*cert_cb)(SSL *ssl, void *arg), void *arg);

 void SSL_set_cert_cb(SSL *s, int (*cert_cb)(SSL *ssl, void *arg), void *arg);

 int (*cert_cb)(SSL *ssl, void *arg);

=head1 DESCRIPTION

SSL_CTX_set_cert_cb() and SSL_set_cert_cb() sets the B<cert_cb()> callback,

B<arg> value is pointer which is passed to the application callback.

When B<cert_cb()> is NULL, no callback function is used.

cert_cb() is the application defined callback. It is called before a

certificate will be used by a client or server. The callback can then inspect

the passed B<ssl> structure and set or clear any appropriate certificates. If

the callback is successful it B<MUST> return 1 even if no certificates have

been set. A zero is returned on error which will abort the handshake with a

fatal internal error alert. A negative return value will suspend the handshake

and the handshake function will return immediately.

L<SSL_get_error(3)|SSL_get_error(3)> will return SSL_ERROR_WANT_X509_LOOKUP to

indicate, that the handshake was suspended. The next call to the handshake

function will again lead to the call of cert_cb(). It is the job of the

cert_cb() to store information about the state of the last call,

if required to continue.

=head1 NOTES

An application will typically call SSL_use_certificate() and

SSL_use_PrivateKey() to set the end entity certificate and private key.

It can add intermediate and optionally the root CA certificates using

SSL_add1_chain_cert().

It might also call SSL_certs_clear() to delete any certificates associated

with the B<SSL> object.

The certificate callback functionality supercedes the (largely broken)

functionality provided by the old client certificate callback interface.

It is B<always> called even is a certificate is already set so the callback

can modify or delete the existing certificate.

A more advanced callback might examine the handshake parameters and set

whatever chain is appropriate. For example a legacy client supporting only

TLS v1.0 might receive a certificate chain signed using SHA1 whereas a

TLS v1.2 client which advertises support for SHA256 could receive a chain

using SHA256.

Normal server sanity checks are performed on any certificates set

by the callback. So if an EC chain is set for a curve the client does not

support it will B<not> be used.

=head1 SEE ALSO

L<ssl(3)|ssl(3)>, L<SSL_use_certificate(3)|SSL_use_certificate(3)>,

L<SSL_add1_chain_cert(3)|SSL_add1_chain_cert(3)>,

L<SSL_get_client_CA_list(3)|SSL_get_client_CA_list(3)>,

L<SSL_clear(3)|SSL_clear(3)>, L<SSL_free(3)|SSL_free(3)>

=cut

=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 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. All export ciphersuites are prohibited since they all offer

less than 80 bits of security. 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. 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 ciphersuite using RC4 is also

prohibited. SSL version 3 is also not allowed. Compression is disabled.

=item B<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 ciphersuites 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. As a result RSA, DSA and DH keys

shorter than 7680 bits and ECC keys shorter than 384 bits are prohibited.

Ciphersuites using SHA1 for the MAC are prohibited. TLS versions below 1.2 are

not permitted.

=item B<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.

=back

=head1 APPLICATION DEFINED SECURITY CALLBACKS

TBA

=head1 NOTES

B<WARNING> at this time setting the security level higher than 1 for

general internet use is likely to cause B<considerable> interoperability

issues and is not recommended. This is because the B<SHA1> algorithm

is very widely used in certificates and will be rejected at levels

higher than 1 because it only offers 80 bits of security.

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.

Some security levels require large key sizes for none-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 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: for example it might

appear that a certificate is not set at all because it had been rejected.

=head1 SEE ALSO

TBA

=head1 HISTORY

These functions were first added to OpenSSL 1.1.0

=cut