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gnutls_prf - Man Page

API function


#include <gnutls/gnutls.h>

int gnutls_prf(gnutls_session_t session, size_t label_size, const char * label, int server_random_first, size_t extra_size, const char * extra, size_t outsize, char * out);


gnutls_session_t session

is a gnutls_session_t type.

size_t label_size

length of the  label variable.

const char * label

label used in PRF computation, typically a short string.

int server_random_first

non-zero if server random field should be first in seed

size_t extra_size

length of the  extra variable.

const char * extra

optional extra data to seed the PRF with.

size_t outsize

size of pre-allocated output buffer to hold the output.

char * out

pre-allocated buffer to hold the generated data.


Applies the TLS Pseudo-Random-Function (PRF) on the master secret and the provided data, seeded with the client and server random fields. For the key expansion specified in RFC5705 see gnutls_prf_rfc5705().

The  label variable usually contains a string denoting the purpose for the generated data.  The  server_random_first indicates whether the client random field or the server random field should be first in the seed.  Non-zero indicates that the server random field is first, 0 that the client random field is first.

The  extra variable can be used to add more data to the seed, after the random variables.  It can be used to make sure the generated output is strongly connected to some additional data (e.g., a string used in user authentication).

The output is placed in  out , which must be pre-allocated.


This function produces identical output with gnutls_prf_rfc5705() when  server_random_first is set to 0 and  extra is NULL. Under TLS1.3 this function will only operate when these conditions are true, or otherwise return GNUTLS_E_INVALID_REQUEST.


GNUTLS_E_SUCCESS on success, or an error code.

Reporting Bugs

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

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



3.8.6 gnutls