---
name: "gnutls_hkdf_expand"
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_hkdf_expand"
---

# gnutls\_hkdf\_expand(3)

API function

## NAME

gnutls\_hkdf\_expand - API function

## SYNOPSIS

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

**int gnutls\_hkdf\_expand(gnutls\_mac\_algorithm\_t** *mac***, const gnutls\_datum\_t \*** *key***, const gnutls\_datum\_t \*** *info***, void \*** *output***, size\_t** *length***);**

## ARGUMENTS

- gnutls\_mac\_algorithm\_t mac

  the mac algorithm used internally

- const gnutls\_datum\_t \* key

  the pseudorandom key created with HKDF-Extract

- const gnutls\_datum\_t \* info

  the optional informational data

- void \* output

  the output value of the expand operation

- size\_t length

  the desired length of the output key

## DESCRIPTION

This function will derive a variable length keying material from the pseudorandom key using the HKDF-Expand function as defined in RFC 5869.

## RETURNS

Zero or a negative error code on error.

## SINCE

3\.6.13

## 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/