---
name: "gnutls_x509_crt_get_key_purpose_oid"
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_purpose_oid"
---

# gnutls\_x509\_crt\_get\_key\_purpose\_oid(3)

API function

## NAME

gnutls\_x509\_crt\_get\_key\_purpose\_oid - API function

## SYNOPSIS

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

**int gnutls\_x509\_crt\_get\_key\_purpose\_oid(gnutls\_x509\_crt\_t** *cert***, unsigned** *indx***, void \*** *oid***, size\_t \*** *oid\_size***, unsigned int \*** *critical***);**

## ARGUMENTS

- gnutls\_x509\_crt\_t cert

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

- unsigned indx

  This specifies which OID to return. Use (0) to get the first one.

- void \* oid

  a pointer to a buffer to hold the OID (may be null)

- size\_t \* oid\_size

  initially holds the size of  *oid*

- unsigned int \* critical

  output flag to indicate criticality of extension

## DESCRIPTION

This function will extract the key purpose OIDs of the Certificate specified by the given index.  These are stored in the Extended Key Usage extension (2.5.29.37) See the GNUTLS\_KP\_\* definitions for human readable names.

If  *oid* is null then only the size will be filled. The  *oid* returned will be null terminated, although  *oid\_size* will not account for the trailing null.

## RETURNS

**GNUTLS\_E\_SHORT\_MEMORY\_BUFFER** if the provided buffer is not long enough, and in that case the \*oid\_size will be updated with the required size.  On success 0 is 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/