@deftypefun {int} {gnutls_prf_rfc5705} (gnutls_session_t @var{session}, size_t @var{label_size}, const char * @var{label}, size_t @var{context_size}, const char * @var{context}, size_t @var{outsize}, char * @var{out})

@var{session}: is a @code{gnutls_session_t}  type.

@var{label_size}: length of the  @code{label} variable.

@var{label}: label used in PRF computation, typically a short string.

@var{context_size}: length of the  @code{extra} variable.

@var{context}: optional extra data to seed the PRF with.

@var{outsize}: size of pre-allocated output buffer to hold the output.

@var{out}: pre-allocated buffer to hold the generated data.

Exports keying material from TLS/DTLS session to an application, as

specified in RFC5705.

In the TLS versions prior to 1.3, it applies the TLS

Pseudo-Random-Function (PRF) on the master secret and the provided

data, seeded with the client and server random fields.

In TLS 1.3, it applies HKDF on the exporter master secret derived

from the master secret.

The  @code{label} variable usually contains a string denoting the purpose

for the generated data.

The  @code{context} 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  @code{out} , which must be pre-allocated.

Note that, to provide the RFC5705 context, the  @code{context} variable

must be non-null.

@strong{Returns:} @code{GNUTLS_E_SUCCESS}  on success, or an error code.

@strong{Since:} 3.4.4

@end deftypefun