---
name: "gnutls_x509_crt_get_key_usage"
section: "3"
platform: "linux"
package: "gnutls"
version: "3.8.13-3"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/gnutls_x509_crt_get_key_usage"
---

# gnutls\_x509\_crt\_get\_key\_usage(3)

API function

## NAME

gnutls\_x509\_crt\_get\_key\_usage - API function

## SYNOPSIS

**#include \<gnutls/x509.h\>**

**int gnutls\_x509\_crt\_get\_key\_usage(gnutls\_x509\_crt\_t** *cert***, unsigned int \*** *key\_usage***, unsigned int \*** *critical***);**

## ARGUMENTS

- gnutls\_x509\_crt\_t cert

  should contain a **gnutls\_x509\_crt\_t** type

- unsigned int \* key\_usage

  where the key usage bits will be stored

- unsigned int \* critical

  will be non-zero if the extension is marked as critical

## DESCRIPTION

This function will return certificate's key usage, by reading the keyUsage X.509 extension (2.5.29.15). The key usage value will ORed values of the: **GNUTLS\_KEY\_DIGITAL\_SIGNATURE**, **GNUTLS\_KEY\_NON\_REPUDIATION**, **GNUTLS\_KEY\_KEY\_ENCIPHERMENT**, **GNUTLS\_KEY\_DATA\_ENCIPHERMENT**, **GNUTLS\_KEY\_KEY\_AGREEMENT**, **GNUTLS\_KEY\_KEY\_CERT\_SIGN**, **GNUTLS\_KEY\_CRL\_SIGN**, **GNUTLS\_KEY\_ENCIPHER\_ONLY**, **GNUTLS\_KEY\_DECIPHER\_ONLY**.

## RETURNS

zero on success, or a negative error code in case of parsing error.  If the certificate does not contain the keyUsage extension **GNUTLS\_E\_REQUESTED\_DATA\_NOT\_AVAILABLE** will be returned.

## REPORTING BUGS

Report bugs to \<bugs@gnutls.org\>.\
 Home page: https://www.gnutls.org

## COPYRIGHT

Copyright © 2001-2023 Free Software Foundation, Inc., and others.\
 Copying and distribution of this file, with or without modification, are permitted in any medium without royalty provided the copyright notice and this notice are preserved.

## SEE ALSO

The full documentation for **gnutls** is maintained as a Texinfo manual. If the /usr/share/doc/gnutls/ directory does not contain the HTML form visit

- https://www.gnutls.org/manual/