DPP2: Add E-id in Reconfig Announcement

Add an encrypted Enrollee identifier into Reconfig Announcement frames
and decrypt that on the Configurator side. The actual E-id value is
currently not used for anything, but it can be used in the future to
provide better control over reconfiguration.

Signed-off-by: Jouni Malinen <jouni@codeaurora.org>

src/ap/dpp_hostapd.c

@@ -1235,8 +1235,8 @@ hostapd_dpp_rx_reconfig_announcement(struct hostapd_data *hapd, const u8 *src,
 				     const u8 *hdr, const u8 *buf, size_t len,
 				     unsigned int freq)
 {
-	const u8 *csign_hash, *fcgroup;
-	u16 csign_hash_len, fcgroup_len;
+	const u8 *csign_hash, *fcgroup, *a_nonce, *e_id;
+	u16 csign_hash_len, fcgroup_len, a_nonce_len, e_id_len;
 	struct dpp_configurator *conf;
 	struct dpp_authentication *auth;
 	unsigned int wait_time, max_wait_time;
@@ -1282,8 +1282,12 @@ hostapd_dpp_rx_reconfig_announcement(struct hostapd_data *hapd, const u8 *src,
 	group = WPA_GET_LE16(fcgroup);
 	wpa_printf(MSG_DEBUG, "DPP: Enrollee finite cyclic group: %u", group);
 
+	a_nonce = dpp_get_attr(buf, len, DPP_ATTR_A_NONCE, &a_nonce_len);
+	e_id = dpp_get_attr(buf, len, DPP_ATTR_E_PRIME_ID, &e_id_len);
+
 	auth = dpp_reconfig_init(hapd->iface->interfaces->dpp, hapd->msg_ctx,
-				 conf, freq, group);
+				 conf, freq, group, a_nonce, a_nonce_len,
+				 e_id, e_id_len);
 	if (!auth)
 		return;
 	hostapd_dpp_set_testing_options(hapd, auth);

src/common/dpp.h

@@ -21,6 +21,7 @@ struct crypto_ecdh;
 struct hostapd_ip_addr;
 struct dpp_global;
 struct json_token;
+struct dpp_reconfig_id;
 
 #ifdef CONFIG_TESTING_OPTIONS
 #define DPP_VERSION (dpp_version_override)
@@ -87,6 +88,8 @@ enum dpp_attribute_id {
 	DPP_ATTR_RECONFIG_FLAGS = 0x101D,
 	DPP_ATTR_C_SIGN_KEY_HASH = 0x101E,
 	DPP_ATTR_CSR_ATTR_REQ = 0x101F,
+	DPP_ATTR_A_NONCE = 0x1020,
+	DPP_ATTR_E_PRIME_ID = 0x1021,
 };
 
 enum dpp_status_error {
@@ -685,10 +688,13 @@ void dpp_global_deinit(struct dpp_global *dpp);
 struct wpabuf * dpp_build_reconfig_announcement(const u8 *csign_key,
 						size_t csign_key_len,
 						const u8 *net_access_key,
-						size_t net_access_key_len);
+						size_t net_access_key_len,
+						struct dpp_reconfig_id *id);
 struct dpp_authentication *
 dpp_reconfig_init(struct dpp_global *dpp, void *msg_ctx,
-		  struct dpp_configurator *conf, unsigned int freq, u16 group);
+		  struct dpp_configurator *conf, unsigned int freq, u16 group,
+		  const u8 *a_nonce_attr, size_t a_nonce_len,
+		  const u8 *e_id_attr, size_t e_id_len);
 struct dpp_authentication *
 dpp_reconfig_auth_req_rx(struct dpp_global *dpp, void *msg_ctx,
 			 const char *own_connector,
@@ -702,5 +708,10 @@ dpp_reconfig_auth_resp_rx(struct dpp_authentication *auth, const u8 *hdr,
 int dpp_reconfig_auth_conf_rx(struct dpp_authentication *auth, const u8 *hdr,
 			      const u8 *attr_start, size_t attr_len);
 
+struct dpp_reconfig_id * dpp_gen_reconfig_id(const u8 *csign_key,
+					     size_t csign_key_len);
+int dpp_update_reconfig_id(struct dpp_reconfig_id *id);
+void dpp_free_reconfig_id(struct dpp_reconfig_id *id);
+
 #endif /* CONFIG_DPP */
 #endif /* DPP_H */

src/common/dpp_crypto.c

@@ -2988,6 +2988,193 @@ fail:
 	return ret;
 }
 
+
+struct dpp_reconfig_id * dpp_gen_reconfig_id(const u8 *csign_key,
+					     size_t csign_key_len)
+{
+	const unsigned char *p;
+	EVP_PKEY *csign = NULL;
+	struct dpp_reconfig_id *id = NULL;
+	BN_CTX *ctx = NULL;
+	BIGNUM *bn = NULL, *q = NULL;
+	const EC_KEY *eckey;
+	const EC_GROUP *group;
+	EC_POINT *e_id = NULL;
+
+	p = csign_key;
+	csign = d2i_PUBKEY(NULL, &p, csign_key_len);
+	if (!csign)
+		goto fail;
+
+	eckey = EVP_PKEY_get0_EC_KEY(csign);
+	if (!eckey)
+		goto fail;
+	group = EC_KEY_get0_group(eckey);
+	if (!group)
+		goto fail;
+
+	e_id = EC_POINT_new(group);
+	ctx = BN_CTX_new();
+	bn = BN_new();
+	q = BN_new();
+	if (!e_id || !ctx || !bn || !q ||
+	    !EC_GROUP_get_order(group, q, ctx) ||
+	    !BN_rand_range(bn, q) ||
+	    !EC_POINT_mul(group, e_id, bn, NULL, NULL, ctx))
+		goto fail;
+
+	dpp_debug_print_point("DPP: Generated random point E-id", group, e_id);
+
+	id = os_zalloc(sizeof(*id));
+	if (!id)
+		goto fail;
+	id->group = group;
+	id->e_id = e_id;
+	e_id = NULL;
+	id->csign = csign;
+	csign = NULL;
+fail:
+	EC_POINT_free(e_id);
+	EVP_PKEY_free(csign);
+	BN_clear_free(bn);
+	BN_CTX_free(ctx);
+	return id;
+}
+
+
+static EVP_PKEY * dpp_pkey_from_point(const EC_GROUP *group,
+				      const EC_POINT *point)
+{
+	EC_KEY *eckey;
+	EVP_PKEY *pkey = NULL;
+
+	eckey = EC_KEY_new();
+	if (!eckey ||
+	    EC_KEY_set_group(eckey, group) != 1 ||
+	    EC_KEY_set_public_key(eckey, point) != 1) {
+		wpa_printf(MSG_ERROR,
+			   "DPP: Failed to set EC_KEY: %s",
+			   ERR_error_string(ERR_get_error(), NULL));
+		goto fail;
+	}
+	EC_KEY_set_asn1_flag(eckey, OPENSSL_EC_NAMED_CURVE);
+
+	pkey = EVP_PKEY_new();
+	if (!pkey || EVP_PKEY_set1_EC_KEY(pkey, eckey) != 1) {
+		wpa_printf(MSG_ERROR, "DPP: Could not create EVP_PKEY");
+		EVP_PKEY_free(pkey);
+		pkey = NULL;
+		goto fail;
+	}
+
+fail:
+	EC_KEY_free(eckey);
+	return pkey;
+}
+
+
+int dpp_update_reconfig_id(struct dpp_reconfig_id *id)
+{
+	BN_CTX *ctx = NULL;
+	BIGNUM *bn = NULL, *q = NULL;
+	EC_POINT *e_prime_id = NULL, *a_nonce = NULL;
+	int ret = -1;
+	const EC_KEY *csign;
+	const EC_POINT *csign_point;
+
+	csign = EVP_PKEY_get0_EC_KEY(id->csign);
+	if (!csign)
+		goto fail;
+	csign_point = EC_KEY_get0_public_key(csign);
+	e_prime_id = EC_POINT_new(id->group);
+	a_nonce = EC_POINT_new(id->group);
+	ctx = BN_CTX_new();
+	bn = BN_new();
+	q = BN_new();
+	/* Generate random 0 <= a-nonce < q
+	 * A-NONCE = a-nonce * G
+	 * E'-id = E-id + a-nonce * S_C */
+	if (!csign_point || !e_prime_id || !a_nonce || !ctx || !bn || !q ||
+	    !EC_GROUP_get_order(id->group, q, ctx) ||
+	    !BN_rand_range(bn, q) || /* bn = a-nonce */
+	    !EC_POINT_mul(id->group, a_nonce, bn, NULL, NULL, ctx) ||
+	    !EC_POINT_mul(id->group, e_prime_id, NULL, csign_point, bn, ctx) ||
+	    !EC_POINT_add(id->group, e_prime_id, id->e_id, e_prime_id, ctx))
+		goto fail;
+
+	dpp_debug_print_point("DPP: Generated A-NONCE", id->group, a_nonce);
+	dpp_debug_print_point("DPP: Encrypted E-id to E'-id",
+			      id->group, e_prime_id);
+
+	EVP_PKEY_free(id->a_nonce);
+	EVP_PKEY_free(id->e_prime_id);
+	id->a_nonce = dpp_pkey_from_point(id->group, a_nonce);
+	id->e_prime_id = dpp_pkey_from_point(id->group, e_prime_id);
+	if (!id->a_nonce || !id->e_prime_id)
+		goto fail;
+
+	ret = 0;
+
+fail:
+	EC_POINT_free(e_prime_id);
+	EC_POINT_free(a_nonce);
+	BN_clear_free(bn);
+	BN_CTX_free(ctx);
+	return ret;
+}
+
+
+void dpp_free_reconfig_id(struct dpp_reconfig_id *id)
+{
+	if (id) {
+		EC_POINT_clear_free(id->e_id);
+		EVP_PKEY_free(id->csign);
+		EVP_PKEY_free(id->a_nonce);
+		EVP_PKEY_free(id->e_prime_id);
+		os_free(id);
+	}
+}
+
+
+EC_POINT * dpp_decrypt_e_id(EVP_PKEY *csign, EVP_PKEY *a_nonce,
+			    EVP_PKEY *e_prime_id)
+{
+	const EC_KEY *csign_ec, *a_nonce_ec, *e_prime_id_ec;
+	const BIGNUM *csign_bn;
+	const EC_GROUP *group;
+	EC_POINT *e_id = NULL;
+	const EC_POINT *a_nonce_point, *e_prime_id_point;
+	BN_CTX *ctx = NULL;
+
+	/* E-id = E'-id - s_C * A-NONCE */
+	csign_ec = EVP_PKEY_get0_EC_KEY(csign);
+	a_nonce_ec = EVP_PKEY_get0_EC_KEY(a_nonce);
+	e_prime_id_ec = EVP_PKEY_get0_EC_KEY(e_prime_id);
+	if (!csign_ec || !a_nonce_ec || !e_prime_id_ec)
+		return NULL;
+	csign_bn = EC_KEY_get0_private_key(csign_ec);
+	group = EC_KEY_get0_group(csign_ec);
+	a_nonce_point = EC_KEY_get0_public_key(a_nonce_ec);
+	e_prime_id_point = EC_KEY_get0_public_key(e_prime_id_ec);
+	ctx = BN_CTX_new();
+	if (!csign_bn || !group || !a_nonce_point || !e_prime_id_point || !ctx)
+		goto fail;
+	e_id = EC_POINT_new(group);
+	if (!e_id ||
+	    !EC_POINT_mul(group, e_id, NULL, a_nonce_point, csign_bn, ctx) ||
+	    !EC_POINT_invert(group, e_id, ctx) ||
+	    !EC_POINT_add(group, e_id, e_prime_id_point, e_id, ctx)) {
+		EC_POINT_clear_free(e_id);
+		goto fail;
+	}
+
+	dpp_debug_print_point("DPP: Decrypted E-id", group, e_id);
+
+fail:
+	BN_CTX_free(ctx);
+	return e_id;
+}
+
 #endif /* CONFIG_DPP2 */
 
 

src/common/dpp_i.h

@@ -133,11 +133,21 @@ int dpp_reconfig_derive_ke_responder(struct dpp_authentication *auth,
 int dpp_reconfig_derive_ke_initiator(struct dpp_authentication *auth,
 				     const u8 *r_proto, u16 r_proto_len,
 				     struct json_token *net_access_key);
+EC_POINT * dpp_decrypt_e_id(EVP_PKEY *csign, EVP_PKEY *a_nonce,
+			    EVP_PKEY *e_prime_id);
 char * dpp_sign_connector(struct dpp_configurator *conf,
 			  const struct wpabuf *dppcon);
 int dpp_test_gen_invalid_key(struct wpabuf *msg,
 			     const struct dpp_curve_params *curve);
 
+struct dpp_reconfig_id {
+	const EC_GROUP *group;
+	EC_POINT *e_id; /* E-id */
+	EVP_PKEY *csign;
+	EVP_PKEY *a_nonce; /* A-NONCE */
+	EVP_PKEY *e_prime_id; /* E'-id */
+};
+
 /* dpp_tcp.c */
 
 void dpp_controller_conn_status_result_wait_timeout(void *eloop_ctx,

src/common/dpp_reconfig.c

@@ -36,7 +36,8 @@ static void dpp_build_attr_csign_key_hash(struct wpabuf *msg, const u8 *hash)
 struct wpabuf * dpp_build_reconfig_announcement(const u8 *csign_key,
 						size_t csign_key_len,
 						const u8 *net_access_key,
-						size_t net_access_key_len)
+						size_t net_access_key_len,
+						struct dpp_reconfig_id *id)
 {
 	struct wpabuf *msg = NULL;
 	EVP_PKEY *csign = NULL;
@@ -49,6 +50,7 @@ struct wpabuf * dpp_build_reconfig_announcement(const u8 *csign_key,
 	size_t attr_len;
 	const struct dpp_curve_params *own_curve;
 	EVP_PKEY *own_key;
+	struct wpabuf *a_nonce = NULL, *e_id = NULL;
 
 	wpa_printf(MSG_DEBUG, "DPP: Build Reconfig Announcement frame");
 
@@ -81,8 +83,20 @@ struct wpabuf * dpp_build_reconfig_announcement(const u8 *csign_key,
 	wpa_hexdump(MSG_DEBUG, "DPP: kid = SHA256(uncompressed C-sign key)",
 		    hash, SHA256_MAC_LEN);
 
+	if (dpp_update_reconfig_id(id) < 0) {
+		wpa_printf(MSG_ERROR, "DPP: Failed to generate E'-id");
+		goto fail;
+	}
+
+	a_nonce = dpp_get_pubkey_point(id->a_nonce, 0);
+	e_id = dpp_get_pubkey_point(id->e_prime_id, 0);
+	if (!a_nonce || !e_id)
+		goto fail;
+
 	attr_len = 4 + SHA256_MAC_LEN;
 	attr_len += 4 + 2;
+	attr_len += 4 + wpabuf_len(a_nonce);
+	attr_len += 4 + wpabuf_len(e_id);
 	msg = dpp_alloc_msg(DPP_PA_RECONFIG_ANNOUNCEMENT, attr_len);
 	if (!msg)
 		goto fail;
@@ -97,9 +111,21 @@ struct wpabuf * dpp_build_reconfig_announcement(const u8 *csign_key,
 	wpabuf_put_le16(msg, 2);
 	wpabuf_put_le16(msg, own_curve->ike_group);
 
+	/* A-NONCE */
+	wpabuf_put_le16(msg, DPP_ATTR_A_NONCE);
+	wpabuf_put_le16(msg, wpabuf_len(a_nonce));
+	wpabuf_put_buf(msg, a_nonce);
+
+	/* E'-id */
+	wpabuf_put_le16(msg, DPP_ATTR_E_PRIME_ID);
+	wpabuf_put_le16(msg, wpabuf_len(e_id));
+	wpabuf_put_buf(msg, e_id);
+
 	wpa_hexdump_buf(MSG_DEBUG,
 			"DPP: Reconfig Announcement frame attributes", msg);
 fail:
+	wpabuf_free(a_nonce);
+	wpabuf_free(e_id);
 	EVP_PKEY_free(own_key);
 	return msg;
 }
@@ -198,10 +224,14 @@ fail:
 
 struct dpp_authentication *
 dpp_reconfig_init(struct dpp_global *dpp, void *msg_ctx,
-		  struct dpp_configurator *conf, unsigned int freq, u16 group)
+		  struct dpp_configurator *conf, unsigned int freq, u16 group,
+		  const u8 *a_nonce_attr, size_t a_nonce_len,
+		  const u8 *e_id_attr, size_t e_id_len)
 {
 	struct dpp_authentication *auth;
 	const struct dpp_curve_params *curve;
+	EVP_PKEY *a_nonce, *e_prime_id;
+	EC_POINT *e_id;
 
 	curve = dpp_get_curve_ike_group(group);
 	if (!curve) {
@@ -211,6 +241,42 @@ dpp_reconfig_init(struct dpp_global *dpp, void *msg_ctx,
 		return NULL;
 	}
 
+	if (!a_nonce_attr) {
+		wpa_printf(MSG_INFO, "DPP: Missing required A-NONCE attribute");
+		return NULL;
+	}
+	wpa_hexdump(MSG_MSGDUMP, "DPP: A-NONCE", a_nonce_attr, a_nonce_len);
+	a_nonce = dpp_set_pubkey_point(conf->csign, a_nonce_attr, a_nonce_len);
+	if (!a_nonce) {
+		wpa_printf(MSG_INFO, "DPP: Invalid A-NONCE");
+		return NULL;
+	}
+	dpp_debug_print_key("A-NONCE", a_nonce);
+
+	if (!e_id_attr) {
+		wpa_printf(MSG_INFO, "DPP: Missing required E'-id attribute");
+		return NULL;
+	}
+	e_prime_id = dpp_set_pubkey_point(conf->csign, e_id_attr, e_id_len);
+	if (!e_prime_id) {
+		wpa_printf(MSG_INFO, "DPP: Invalid E'-id");
+		EVP_PKEY_free(a_nonce);
+		return NULL;
+	}
+	dpp_debug_print_key("E'-id", e_prime_id);
+	e_id = dpp_decrypt_e_id(conf->csign, a_nonce, e_prime_id);
+	EVP_PKEY_free(a_nonce);
+	EVP_PKEY_free(e_prime_id);
+	if (!e_id) {
+		wpa_printf(MSG_INFO, "DPP: Could not decrypt E'-id");
+		return NULL;
+	}
+	/* TODO: could use E-id to determine whether reconfiguration with this
+	 * Enrollee has already been started and is waiting for updated
+	 * configuration instead of replying again before such configuration
+	 * becomes available */
+	EC_POINT_clear_free(e_id);
+
 	auth = dpp_alloc_auth(dpp, msg_ctx);
 	if (!auth)
 		return NULL;

src/common/dpp_tcp.c

@@ -844,8 +844,8 @@ static int dpp_controller_rx_reconfig_announcement(struct dpp_connection *conn,
 						   const u8 *hdr, const u8 *buf,
 						   size_t len)
 {
-	const u8 *csign_hash, *fcgroup;
-	u16 csign_hash_len, fcgroup_len;
+	const u8 *csign_hash, *fcgroup, *a_nonce, *e_id;
+	u16 csign_hash_len, fcgroup_len, a_nonce_len, e_id_len;
 	struct dpp_configurator *conf;
 	struct dpp_global *dpp = conn->ctrl->global;
 	struct dpp_authentication *auth;
@@ -885,7 +885,11 @@ static int dpp_controller_rx_reconfig_announcement(struct dpp_connection *conn,
 	group = WPA_GET_LE16(fcgroup);
 	wpa_printf(MSG_DEBUG, "DPP: Enrollee finite cyclic group: %u", group);
 
-	auth = dpp_reconfig_init(dpp, dpp->msg_ctx, conf, 0, group);
+	a_nonce = dpp_get_attr(buf, len, DPP_ATTR_A_NONCE, &a_nonce_len);
+	e_id = dpp_get_attr(buf, len, DPP_ATTR_E_PRIME_ID, &e_id_len);
+
+	auth = dpp_reconfig_init(dpp, dpp->msg_ctx, conf, 0, group,
+				 a_nonce, a_nonce_len, e_id, e_id_len);
 	if (!auth)
 		return -1;
 	if (dpp_set_configurator(auth, conn->ctrl->configurator_params) < 0) {

wpa_supplicant/dpp_supplicant.c

@@ -2022,8 +2022,8 @@ wpas_dpp_rx_reconfig_announcement(struct wpa_supplicant *wpa_s, const u8 *src,
 				  const u8 *hdr, const u8 *buf, size_t len,
 				  unsigned int freq)
 {
-	const u8 *csign_hash, *fcgroup;
-	u16 csign_hash_len, fcgroup_len;
+	const u8 *csign_hash, *fcgroup, *a_nonce, *e_id;
+	u16 csign_hash_len, fcgroup_len, a_nonce_len, e_id_len;
 	struct dpp_configurator *conf;
 	struct dpp_authentication *auth;
 	unsigned int wait_time, max_wait_time;
@@ -2067,7 +2067,11 @@ wpas_dpp_rx_reconfig_announcement(struct wpa_supplicant *wpa_s, const u8 *src,
 	group = WPA_GET_LE16(fcgroup);
 	wpa_printf(MSG_DEBUG, "DPP: Enrollee finite cyclic group: %u", group);
 
-	auth = dpp_reconfig_init(wpa_s->dpp, wpa_s, conf, freq, group);
+	a_nonce = dpp_get_attr(buf, len, DPP_ATTR_A_NONCE, &a_nonce_len);
+	e_id = dpp_get_attr(buf, len, DPP_ATTR_E_PRIME_ID, &e_id_len);
+
+	auth = dpp_reconfig_init(wpa_s->dpp, wpa_s, conf, freq, group,
+				 a_nonce, a_nonce_len, e_id, e_id_len);
 	if (!auth)
 		return;
 	wpas_dpp_set_testing_options(wpa_s, auth);
@@ -3303,6 +3307,8 @@ void wpas_dpp_deinit(struct wpa_supplicant *wpa_s)
 	dpp_pfs_free(wpa_s->dpp_pfs);
 	wpa_s->dpp_pfs = NULL;
 	wpas_dpp_chirp_stop(wpa_s);
+	dpp_free_reconfig_id(wpa_s->dpp_reconfig_id);
+	wpa_s->dpp_reconfig_id = NULL;
 #endif /* CONFIG_DPP2 */
 	offchannel_send_action_done(wpa_s);
 	wpas_dpp_listen_stop(wpa_s);
@@ -3642,14 +3648,25 @@ int wpas_dpp_reconfig(struct wpa_supplicant *wpa_s, struct wpa_ssid *ssid)
 		return -1;
 	}
 
+	dpp_free_reconfig_id(wpa_s->dpp_reconfig_id);
+	wpa_s->dpp_reconfig_id = dpp_gen_reconfig_id(ssid->dpp_csign,
+						     ssid->dpp_csign_len);
+	if (!wpa_s->dpp_reconfig_id) {
+		wpa_printf(MSG_DEBUG,
+			   "DPP: Failed to generate E-id for reconfiguration");
+		return -1;
+	}
 	wpas_dpp_chirp_stop(wpa_s);
 	wpa_s->dpp_allowed_roles = DPP_CAPAB_ENROLLEE;
 	wpa_s->dpp_qr_mutual = 0;
+	/* TODO: regenerate Reconfig Announcement frame to update A-NONCE/E'-id
+	 * for each retransmission */
 	wpa_s->dpp_reconfig_announcement =
 		dpp_build_reconfig_announcement(ssid->dpp_csign,
 						ssid->dpp_csign_len,
 						ssid->dpp_netaccesskey,
-						ssid->dpp_netaccesskey_len);
+						ssid->dpp_netaccesskey_len,
+						wpa_s->dpp_reconfig_id);
 	if (!wpa_s->dpp_reconfig_announcement)
 		return -1;
 	wpa_s->dpp_reconfig_ssid = ssid;

wpa_supplicant/wpa_supplicant_i.h

@@ -1296,6 +1296,7 @@ struct wpa_supplicant {
 	int dpp_chirp_listen;
 	struct wpa_ssid *dpp_reconfig_ssid;
 	int dpp_reconfig_ssid_id;
+	struct dpp_reconfig_id *dpp_reconfig_id;
 #endif /* CONFIG_DPP2 */
 #ifdef CONFIG_TESTING_OPTIONS
 	char *dpp_config_obj_override;