X509_GET_EXTENSION_FLAGS(3)

NAME
X509_get_extension_flags, X509_get_key_usage, X509_get_extended_key_usage - retrieve certificate extension data

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);

DESCRIPTION
These functions retrieve information related to commonly used certificate extensions.

X509_get_extension_flags() retrieves general information about a certificate. It returns one or more of the following flags OR'ed together.

EXFLAG_V1
    The certificate is an obsolete version 1 certificate.

EXFLAG_BCONS
    The certificate contains a basic constraints extension.

EXFLAG_CA
    The certificate contains basic constraints and asserts the CA flag.

EXFLAG_PROXY
    The certificate is a valid proxy certificate. In LibreSSL this flag is never set.

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

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

EXFLAG_FRESHEST
    The freshest CRL extension is present in the certificate.

EXFLAG_CRITICAL
    The certificate contains an unhandled critical extension.

EXFLAG_INVALID
    Some certificate extension values are invalid or inconsistent. The certificate should be rejected. This bit may also be raised after an out-of-memory error while processing the X509 object, so it may not be related to the processed ASN1 object itself.

EXFLAG_INVALID_POLICY
    The NID_certificate_policies certificate extension is invalid or inconsistent. The certificate should be rejected. This bit may also be raised after an out-of-memory error while processing the X509 object, so it may not be related to the processed ASN1 object itself.

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

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

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

The following aliases for these flags are defined in <openssl/x509.h>: X509v3_KU_DIGITAL_SIGNATURE, X509v3_KU_NON_REPUDIATION, X509v3_KU_KEY_ENCIPHERMENT, X509v3_KU_DATA_ENCIPHERMENT, X509v3_KU_KEY_AGREEMENT, X509v3_KU_KEY_CERT_SIGN, X509v3_KU_CRL_SIGN, X509v3_KU_ENCIPHER_ONLY, and X509v3_KU_DECIPHER_ONLY.

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

The value of the flags correspond to extension values which are cached in the X509 structure. If the flags returned do not provide sufficient information, an application should examine extension values directly, for example using X509_get_ext_d2i(3).

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 UINT32_MAX when the corresponding extension is absent. Applications can additionally check the return value of X509_get_extension_flags() and take appropriate action if an extension is absent.

RETURN VALUES
X509_get_extension_flags(), X509_get_key_usage() and X509_get_extended_key_usage() return sets of flags corresponding to the certificate extension values.

SEE ALSO
BASIC_CONSTRAINTS_new(3), EXTENDED_KEY_USAGE_new(3), POLICYINFO_new(3), X509_check_ca(3), X509_check_purpose(3), X509_EXTENSION_new(3), X509_get_ext_d2i(3), X509_get_subject_name(3), X509_get_version(3), X509_new(3)

HISTORY
X509_get_extension_flags, X509_get_key_usage, and X509_get_extended_key_usage first appeared in OpenSSL 1.1.0 and have been available since OpenBSD 7.1.