NAME

       X509_get0_subject_key_id, X509_get0_authority_key_id, X509_get0_authority_issuer,
       X509_get0_authority_serial, X509_get_pathlen, X509_get_extension_flags,
       X509_get_key_usage, X509_get_extended_key_usage, X509_set_proxy_flag,
       X509_set_proxy_pathlen, X509_get_proxy_pathlen - retrieve certificate extension data

SYNOPSIS

        #include <openssl/x509v3.h>

        long X509_get_pathlen(X509 *x);
        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);
        const ASN1_OCTET_STRING *X509_get0_authority_key_id(X509 *x);
        const GENERAL_NAMES *X509_get0_authority_issuer(X509 *x);
        const ASN1_INTEGER *X509_get0_authority_serial(X509 *x);
        void X509_set_proxy_flag(X509 *x);
        void X509_set_proxy_pathlen(int l);
        long X509_get_proxy_pathlen(X509 *x);

DESCRIPTION

       These functions retrieve information related to commonly used certificate extensions.

       X509_get_pathlen() retrieves the path length extension from a certificate.  This extension
       is used to limit the length of a cert chain that may be issued from that CA.

       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.  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_NO_FINGERPRINT
           Failed to compute the internal SHA1 hash value of the certificate or CRL.  This may be
           due to malloc failure or because no SHA1 implementation was found.

       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 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_get0_subject_key_id() returns 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.

       X509_get0_authority_key_id() returns an internal pointer to the authority key identifier
       of x as an ASN1_OCTET_STRING or NULL if the extension is not present or cannot be parsed.

       X509_get0_authority_issuer() returns an internal pointer to the authority certificate
       issuer of x as a stack of GENERAL_NAME structures or NULL if the extension is not present
       or cannot be parsed.

       X509_get0_authority_serial() returns an internal pointer to the authority certificate
       serial number of x as an ASN1_INTEGER or NULL if the extension is not present or cannot be
       parsed.

       X509_set_proxy_flag() marks the certificate with the EXFLAG_PROXY flag.  This is for the
       users who need to mark non-RFC3820 proxy certificates as such, as OpenSSL only detects
       RFC3820 compliant ones.

       X509_set_proxy_pathlen() sets the proxy certificate path length for the given certificate
       x.  This is for the users who need to mark non-RFC3820 proxy certificates as such, as
       OpenSSL only detects RFC3820 compliant ones.

       X509_get_proxy_pathlen() returns the proxy certificate path length for the given
       certificate x if it is a proxy certificate.

NOTES

       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().

RETURN VALUES

       X509_get_pathlen() returns the path length value, or -1 if the extension is not present.

       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.

       X509_get_proxy_pathlen() returns the path length value if the given certificate is a proxy
       one and has a path length set, and -1 otherwise.

SEE ALSO

       X509_check_purpose(3)

HISTORY

       X509_get_pathlen(), X509_set_proxy_flag(), X509_set_proxy_pathlen() and
       X509_get_proxy_pathlen() were added in OpenSSL 1.1.0.

COPYRIGHT

       Copyright 2015-2021 The OpenSSL Project Authors. All Rights Reserved.

       Licensed under the Apache License 2.0 (the "License").  You may not use this file except
       in compliance with the License.  You can obtain a copy in the file LICENSE in the source
       distribution or at <https://www.openssl.org/source/license.html>.