Enhance crypto abstract API for DH

The patch offers alternate implementations of some functions using the
abstract cryptographic API.

This work was done in preparation for the changes to allow hostap to be
compiled with the wolfSSL cryptography and TLS library.

Signed-off-by: Sean Parkinson <sean@wolfssl.com>

src/crypto/dh_groups.c

@@ -1203,19 +1203,6 @@ struct wpabuf * dh_init(const struct dh_group *dh, struct wpabuf **priv)
 	if (*priv == NULL)
 		return NULL;
 
-	if (random_get_bytes(wpabuf_put(*priv, dh->prime_len), dh->prime_len))
-	{
-		wpabuf_clear_free(*priv);
-		*priv = NULL;
-		return NULL;
-	}
-
-	if (os_memcmp(wpabuf_head(*priv), dh->prime, dh->prime_len) > 0) {
-		/* Make sure private value is smaller than prime */
-		*(wpabuf_mhead_u8(*priv)) = 0;
-	}
-	wpa_hexdump_buf_key(MSG_DEBUG, "DH: private value", *priv);
-
 	pv_len = dh->prime_len;
 	pv = wpabuf_alloc(pv_len);
 	if (pv == NULL) {
@@ -1223,17 +1210,17 @@ struct wpabuf * dh_init(const struct dh_group *dh, struct wpabuf **priv)
 		*priv = NULL;
 		return NULL;
 	}
-	if (crypto_mod_exp(dh->generator, dh->generator_len,
-			   wpabuf_head(*priv), wpabuf_len(*priv),
-			   dh->prime, dh->prime_len, wpabuf_mhead(pv),
-			   &pv_len) < 0) {
+	if (crypto_dh_init(*dh->generator, dh->prime, dh->prime_len,
+			   wpabuf_mhead(*priv), wpabuf_mhead(pv)) < 0) {
 		wpabuf_clear_free(pv);
-		wpa_printf(MSG_INFO, "DH: crypto_mod_exp failed");
+		wpa_printf(MSG_INFO, "DH: crypto_dh_init failed");
 		wpabuf_clear_free(*priv);
 		*priv = NULL;
 		return NULL;
 	}
-	wpabuf_put(pv, pv_len);
+	wpabuf_put(*priv, dh->prime_len);
+	wpabuf_put(pv, dh->prime_len);
+	wpa_hexdump_buf_key(MSG_DEBUG, "DH: private value", *priv);
 	wpa_hexdump_buf(MSG_DEBUG, "DH: public value", pv);
 
 	return pv;
@@ -1261,12 +1248,14 @@ struct wpabuf * dh_derive_shared(const struct wpabuf *peer_public,
 	shared = wpabuf_alloc(shared_len);
 	if (shared == NULL)
 		return NULL;
-	if (crypto_mod_exp(wpabuf_head(peer_public), wpabuf_len(peer_public),
-			   wpabuf_head(own_private), wpabuf_len(own_private),
-			   dh->prime, dh->prime_len,
-			   wpabuf_mhead(shared), &shared_len) < 0) {
+	if (crypto_dh_derive_secret(*dh->generator, dh->prime, dh->prime_len,
+				    wpabuf_head(own_private),
+				    wpabuf_len(own_private),
+				    wpabuf_head(peer_public),
+				    wpabuf_len(peer_public),
+				    wpabuf_mhead(shared), &shared_len) < 0) {
 		wpabuf_clear_free(shared);
-		wpa_printf(MSG_INFO, "DH: crypto_mod_exp failed");
+		wpa_printf(MSG_INFO, "DH: crypto_dh_derive_secret failed");
 		return NULL;
 	}
 	wpabuf_put(shared, shared_len);