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Manual Reference Pages  -  X509_GET_EXTENSION_FLAGS (3)

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X509_get_extension_flags, X509_get_key_usage, X509_get_extended_key_usage - retrieve certificate extension flags.



   #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);
   const ASN1_OCTET_STRING *X509_get0_subject_key_id(X509 *x);


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.
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.
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.
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 will return zero or more of the 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 then 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: 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.

X509_get_extended_key_usage() return an internal pointer to the subject key identifier of x as an ASN1_OCTET_STRING or NULL if the extension is not present or cannot be parsed.


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().

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 is an extension is absent.

If X509_get0_subject_key_id() returns NULL then the extension may be absent or malformed. Applications can determine the precise reason using X509_get_ext_d2i().


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

X509_get0_subject_key_id() returns the subject key identifier as a pointer to an ASN1_OCTET_STRING structure or NULL if the extension is absent or an error occurred during parsing.


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1.1.0-pre3 X509_GET_EXTENSION_FLAGS (3) 2016-02-15

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