tls-hkdf: Add helper method to allocate data from the internal PRF

src/libtls/tls_hkdf.c

@@ -485,6 +485,14 @@ METHOD(tls_hkdf_t, derive_finished, bool,
 								 finished);
 }
 
+METHOD(tls_hkdf_t, allocate_bytes, bool,
+	private_tls_hkdf_t *this, chunk_t key, chunk_t seed,
+	chunk_t *out)
+{
+	return this->prf->set_key(this->prf, key) &&
+		   this->prf->allocate_bytes(this->prf, seed, out);
+}
+
 METHOD(tls_hkdf_t, destroy, void,
 	private_tls_hkdf_t *this)
 {
@@ -525,6 +533,7 @@ tls_hkdf_t *tls_hkdf_create(hash_algorithm_t hash_algorithm, chunk_t psk)
 			.derive_key = _derive_key,
 			.derive_iv = _derive_iv,
 			.derive_finished = _derive_finished,
+			.allocate_bytes = _allocate_bytes,
 			.destroy = _destroy,
 		},
 		.phase = HKDF_PHASE_0,

src/libtls/tls_hkdf.h

@@ -111,6 +111,19 @@ struct tls_hkdf_t {
 	bool (*derive_finished)(tls_hkdf_t *this, bool is_server,
 							chunk_t *finished);
 
+	/**
+	 * Use the internal PRF to allocate data (mainly for the finished message
+	 * where the key is from derive_finished() and the seed is the transcript
+	 * hash).
+	 *
+	 * @param key				key to use with the PRF
+	 * @param seed				seed to use with the PRF
+	 * @param out				output from the PRF (allocated)
+	 * @return					TRUE if output was generated
+	 */
+	bool (*allocate_bytes)(tls_hkdf_t *this, chunk_t key, chunk_t seed,
+						   chunk_t *out);
+
 	/**
 	 * Destroy a tls_hkdf_t
 	 */