=pod

=head1 NAME

X509_get_extension_flags, X509_get_key_usage, X509_get_extended_key_usage -
retrieve certificate extension flags.

=head1 SYNOPSIS

   #include <openssl/x509v3.h>

   uint32_t X509_get_extension_flags(X509 *x);
   uint32_t X509_get_key_usage(X509 *x);
   uint32_t X509_get_extended_key_usage(X509 *x);

=head1 DESCRIPTION

These functions retrieve flags related to commonly used certificate extensions.

X509_get_extension_flags() retrieves general information about a certificate,
it will return one or more of the following flags ored together.

=over 4

=item B<EXFLAG_V1>

The certificate is an obsolete version 1 certificate.

=item B<EXFLAG_BCONS>

The certificate contains a basic constraints extension.

=item B<EXFLAG_CA>

The certificate contains basic constraints and asserts the CA flag.

=item B<EXFLAG_PROXY>

The certificate is a valid proxy certificate.

=item B<EXFLAG_SI>

The certificate is self issued (that is subject and issuer names match).

=item B<EXFLAG_SS>

The subject and issuer names match and extension values imply it is self
signed.

=item B<EXFLAG_FRESHEST>

The freshest CRL extension is present in the certificate.

=item B<EXFLAG_CRITICAL>

The certificate contains an unhandled critical extension.

=item B<EXFLAG_INVALID>

Some certificate extension values are invalid or inconsistent. The
certificate should be rejected.

=item B<EXFLAG_KUSAGE>

The certificate contains a key usage extension. The value can be retrieved
using X509_get_key_usage().

=item B<EXFLAG_XKUSAGE>

The certificate contains an extended key usage extension. The value can be
retrieved using X509_get_extended_key_usage().

=back

X509_get_key_usage() returns the value of the key usage extension.  If key
usage is present will return zero or more of the flags:
B<KU_DIGITAL_SIGNATURE>, B<KU_NON_REPUDIATION>, B<KU_KEY_ENCIPHERMENT>,
B<KU_DATA_ENCIPHERMENT>, B<KU_KEY_AGREEMENT>, B<KU_KEY_CERT_SIGN>,
B<KU_CRL_SIGN>, B<KU_ENCIPHER_ONLY> or B<KU_DECIPHER_ONLY> corresponding to
individual key usage bits. If key usage is absent then B<UINT32_MAX> is
returned.

X509_get_extended_key_usage() returns the value of the extended key usage
extension. If extended key usage is present it will return zero or more of the
flags: B<XKU_SSL_SERVER>, B<XKU_SSL_CLIENT>, B<XKU_SMIME>, B<XKU_CODE_SIGN>
B<XKU_OCSP_SIGN>, B<XKU_TIMESTAMP>, B<XKU_DVCS> or B<XKU_ANYEKU>. These
correspond to the OIDs B<id-kp-serverAuth>, B<id-kp-clientAuth>,
B<id-kp-emailProtection>, B<id-kp-codeSigning>, B<id-kp-OCSPSigning>,
B<id-kp-timeStamping>, B<id-kp-dvcs> and B<anyExtendedKeyUsage> respectively.
Additionally B<XKU_SGC> is set if either Netscape or Microsoft SGC OIDs are
present.

=head1 NOTES

The value of the flags correspond to extension values which are cached
in the B<X509> structure. If the flags returned do not provide sufficient
information an application should examine extension values directly.

If the key usage or extended key usage extension is absent then typically usage
is unrestricted. For this reason X509_get_key_usage() and
X509_get_extended_key_usage() return B<UINT32_MAX> when the corresponding
extension is absent. Applications can additionally check the return value of
X509_get_extension_flags() and take appropriate action is an extension is
absent.

=head1 RETURN VALUE

These functions all return sets of flags corresponding to the certificate
extension values.

=head1 SEE ALSO

L<X509_check_purpose(3)>

=cut