- NAME
- SYNOPSIS
- DESCRIPTION
- NOTES
- RETURN VALUES
- SEE ALSO
- HISTORY
- COPYRIGHT

# 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(const X509 *x);
    uint32_t X509_get_extension_flags(const X509 *x);
    uint32_t X509_get_key_usage(const X509 *x);
    uint32_t X509_get_extended_key_usage(const X509 *x);
    const ASN1_OCTET_STRING *X509_get0_subject_key_id(const X509 *x);
    const ASN1_OCTET_STRING *X509_get0_authority_key_id(const X509 *x);
    const GENERAL_NAMES *X509_get0_authority_issuer(const X509 *x);
    const ASN1_INTEGER *X509_get0_authority_serial(const X509 *x);
    void X509_set_proxy_flag(X509 *x);
    void X509_set_proxy_pathlen(int l);
    long X509_get_proxy_pathlen(const 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 2015-2026 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.