X509_GET_EXTENSION_FLAGS(3SSL)

📦
version 4.0.3 · 13 versions
, in ubuntu stonking

💖 X509_GET_EXTENSION_FLAGS 💖

okay bestie, this is from the OpenSSL manual set, section 3SSL — it's giving "certificate extension gossip hotline" and honestly? iconic. ✨

✨ NAME ✨

So basically there's a whole little squad of functions here, and they all do the same general vibe: retrieve certificate extension data. Meet the girls:

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 🎀

🌈 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 pull out info about the certificate extensions that everybody keeps using. It's giving very commonly used extensions, no cap.

🦋 X509_get_pathlen()

Grabs the path length extension out of a certificate. That extension is literally there to cap how long a cert chain issued from that CA can get. Keeping it short, periodt.

👑 X509_get_extension_flags()

Bestie, this one gives you the general tea about a certificate. It returns one or more of these flags, ored together (yes, "ored", that's the word, eat it):

  • EXFLAG_V1 — the certificate is an obsolete version 1 certificate. ancient 💀
  • EXFLAG_BCONS — the certificate contains a basic constraints extension.
  • EXFLAG_CA — the certificate contains basic constraints and asserts the CA flag. main character CA energy.
  • EXFLAG_PROXY — the certificate is a valid proxy certificate.
  • EXFLAG_SI — the certificate is self issued, meaning subject and issuer names match.
  • EXFLAG_SS — the subject and issuer names match and the extension values imply it is self signed.
  • EXFLAG_FRESHEST — the freshest CRL extension is present in the certificate. freshest, literally in the name 🍓
  • 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 it'll hand you zero or more of these flags, each one matching an individual key usage bit:

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.

If key usage is absent then UINT32_MAX is returned. yes fr, that's the "idk, nothing here" number.

✨ X509_get_extended_key_usage()

Returns the value of the extended key usage extension. If extended key usage is present it'll return 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.

🎀 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 one's for the users who need to mark non-RFC3820 proxy certificates as such, because OpenSSL only detects RFC3820 compliant ones. so it's the "manual override" girlie.

🦋 X509_set_proxy_pathlen()

Sets the proxy certificate path length for the given certificate x. Again, this is for the users who need to mark non-RFC3820 proxy certificates as such, because OpenSSL only detects RFC3820 compliant ones.

🌈 X509_get_proxy_pathlen()

Returns the proxy certificate path length for the given certificate x, if it's a proxy certificate.

📝 NOTES 📝

The value of the flags corresponds to extension values that are cached in the X509 structure. So if the flags you get back don't give you enough info, your app should go look at extension values directly — for example using X509_get_ext_d2i().

If the key usage or extended key usage extension is absent, then usage is typically unrestricted. That's why 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.

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. throwback era, lowkey.

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>.

okay that's the whole page bestie, every flag, every NULL, every -1 accounted for 💀 study it and slay your cert parsing era 👑

so anyway, this was version 4.0.3, dated 2026-09-29, and it lives in the X509_GET_EXTENSION_FLAGS(3SSL) corner of the OpenSSL manual. mwah, bye 🫶✨💅

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