l2tp: Full hidden AVPs support

Add option "hide-avps" in the "l2tp" section for hiding attributes
sent to peer. This same option is also made available on accel-ppp's
command line interface:
  accel-ppp# tunnel create tunnel peer-addr 192.0.2.1 hide-avps 1

Attribute hiding is performed upon attribute creation (in the
l2tp_packet_add_*() functions family) rather than upon packet sending.
This avoid running the cipher for every retransmission; the counterpart
is that l2tp_packet_print() can't dump original attributes of hidden
AVPs.

Currently, only one random vector is used for all hidden AVPs in a
packet. This is easily extensible though, as the 'last_RV' field in
struct l2tp_packet_t may be overridden to use new vectors for next
AVPs.

Signed-off-by: Guillaume Nault <g.nault@alphalink.fr>

4 files changed, 318 insertions, 48 deletions

diff --git a/accel-pppd/accel-ppp.conf.5 b/accel-pppd/accel-ppp.conf.5
index 0854021..636fe18 100644
--- a/accel-pppd/accel-ppp.conf.5
+++ b/accel-pppd/accel-ppp.conf.5
@@ -424,6 +424,12 @@ is greater of zero then l2tp module will produce verbose logging.
 .TP
 .BI "secret=" string
 Specifies secret to connect to server.
+.TP
+.BI "hide-avps=" n
+If this option is given and
+.B n
+is greater than 0, then attributes sent in L2TP packets will be hidden (for
+AVPs that support it).
 .SH [radius]
 .br
 Configuration of RADIUS module.
diff --git a/accel-pppd/ctrl/l2tp/l2tp.c b/accel-pppd/ctrl/l2tp/l2tp.c
index c6ba82f..d2c6982 100644
--- a/accel-pppd/ctrl/l2tp/l2tp.c
+++ b/accel-pppd/ctrl/l2tp/l2tp.c
@@ -49,6 +49,7 @@
 #define STATE_CLOSE      0
 
 int conf_verbose = 0;
+int conf_hide_avps = 0;
 int conf_avp_permissive = 0;
 static int conf_timeout = 60;
 static int conf_rtimeout = 5;
@@ -78,6 +79,7 @@ struct l2tp_sess_t
 
 	int state1;
 	uint16_t lns_mode:1;
+	uint16_t hide_avps:1;
 
 	struct triton_context_t sctx;
 	struct triton_timer_t timeout_timer;
@@ -101,6 +103,7 @@ struct l2tp_conn_t
 	uint16_t peer_tid;
 	uint32_t framing_cap;
 	uint16_t lns_mode:1;
+	uint16_t hide_avps:1;
 	uint16_t port_set:1;
 	uint16_t challenge_len;
 	uint8_t *challenge;
@@ -414,7 +417,8 @@ static int l2tp_send_StopCCN(struct l2tp_conn_t *conn,
 		   res, err);
 
 	pack = l2tp_packet_alloc(2, Message_Type_Stop_Ctrl_Conn_Notify,
-				 &conn->peer_addr);
+				 &conn->peer_addr, conn->hide_avps,
+				 conf_secret, conf_secret_len);
 	if (pack == NULL) {
 		log_tunnel(log_error, conn, "impossible to send StopCCN:"
 			   " packet allocation failed\n");
@@ -456,7 +460,8 @@ static int l2tp_send_CDN(struct l2tp_sess_t *sess, uint16_t res, uint16_t err)
 		    res, err);
 
 	pack = l2tp_packet_alloc(2, Message_Type_Call_Disconnect_Notify,
-				 &sess->paren_conn->peer_addr);
+				 &sess->paren_conn->peer_addr, sess->hide_avps,
+				 conf_secret, conf_secret_len);
 	if (pack == NULL) {
 		log_session(log_error, sess, "impossible to send CDN:"
 			    " packet allocation failed\n");
@@ -500,7 +505,8 @@ static int l2tp_tunnel_send_CDN(uint16_t sid, uint16_t peer_sid,
 		   res, err);
 
 	pack = l2tp_packet_alloc(2, Message_Type_Call_Disconnect_Notify,
-				 &conn->peer_addr);
+				 &conn->peer_addr, conn->hide_avps,
+				 conf_secret, conf_secret_len);
 	if (pack == NULL) {
 		log_tunnel(log_error, conn, "impossible to send CDN:"
 			   " packet allocation failed\n");
@@ -863,6 +869,7 @@ static struct l2tp_sess_t *l2tp_tunnel_alloc_session(struct l2tp_conn_t *conn)
 	sess->peer_sid = 0;
 	sess->state1 = STATE_CLOSE;
 	sess->lns_mode = conn->lns_mode;
+	sess->hide_avps = conn->hide_avps;
 
 	sess->sctx.before_switch = log_switch;
 	sess->sctx.close = l2tp_sess_close;
@@ -990,7 +997,8 @@ err:
 static struct l2tp_conn_t *l2tp_tunnel_alloc(const struct sockaddr_in *peer,
 					     const struct sockaddr_in *host,
 					     uint32_t framing_cap,
-					     int lns_mode, int port_set)
+					     int lns_mode, int port_set,
+					     int hide_avps)
 {
 	struct l2tp_conn_t *conn;
 	socklen_t hostaddrlen = sizeof(conn->host_addr);
@@ -1119,6 +1127,7 @@ static struct l2tp_conn_t *l2tp_tunnel_alloc(const struct sockaddr_in *peer,
 	conn->sess_count = 0;
 	conn->lns_mode = lns_mode;
 	conn->port_set = port_set;
+	conn->hide_avps = hide_avps;
 
 	return conn;
 
@@ -1458,7 +1467,7 @@ static int l2tp_send_ZLB(struct l2tp_conn_t *conn)
 
 	log_tunnel(log_debug, conn, "sending ZLB\n");
 
-	pack = l2tp_packet_alloc(2, 0, &conn->peer_addr);
+	pack = l2tp_packet_alloc(2, 0, &conn->peer_addr, 0, NULL, 0);
 	if (!pack) {
 		log_tunnel(log_error, conn, "impossible to send ZLB:"
 			   " packet allocation failed\n");
@@ -1481,7 +1490,8 @@ static void l2tp_send_HELLO(struct triton_timer_t *t)
 
 	log_tunnel(log_debug, conn, "sending HELLO\n");
 
-	pack = l2tp_packet_alloc(2, Message_Type_Hello, &conn->peer_addr);
+	pack = l2tp_packet_alloc(2, Message_Type_Hello, &conn->peer_addr,
+				 conn->hide_avps, conf_secret, conf_secret_len);
 	if (!pack) {
 		log_tunnel(log_error, conn, "impossible to send HELLO:"
 			   " packet allocation failed\n");
@@ -1501,7 +1511,8 @@ static void l2tp_send_SCCRQ(void *peer_addr)
 	log_tunnel(log_info2, conn, "sending SCCRQ\n");
 
 	pack = l2tp_packet_alloc(2, Message_Type_Start_Ctrl_Conn_Request,
-				 &conn->peer_addr);
+				 &conn->peer_addr, conn->hide_avps,
+				 conf_secret, conf_secret_len);
 	if (pack == NULL) {
 		log_tunnel(log_error, conn, "impossible to send SCCRQ:"
 			   " packet allocation failed\n");
@@ -1566,7 +1577,8 @@ static void l2tp_send_SCCRP(struct l2tp_conn_t *conn)
 	log_tunnel(log_info2, conn, "sending SCCRP\n");
 
 	pack = l2tp_packet_alloc(2, Message_Type_Start_Ctrl_Conn_Reply,
-				 &conn->peer_addr);
+				 &conn->peer_addr, conn->hide_avps,
+				 conf_secret, conf_secret_len);
 	if (!pack) {
 		log_tunnel(log_error, conn, "impossible to send SCCRP:"
 			   " packet allocation failed\n");
@@ -1637,7 +1649,8 @@ static int l2tp_send_SCCCN(struct l2tp_conn_t *conn)
 	log_tunnel(log_info2, conn, "sending SCCCN\n");
 
 	pack = l2tp_packet_alloc(2, Message_Type_Start_Ctrl_Conn_Connected,
-				 &conn->peer_addr);
+				 &conn->peer_addr, conn->hide_avps,
+				 conf_secret, conf_secret_len);
 	if (pack == NULL) {
 		log_tunnel(log_error, conn, "impossible to send SCCCN:"
 			   " packet allocation failed\n");
@@ -1673,7 +1686,8 @@ static int l2tp_send_ICRQ(struct l2tp_sess_t *sess)
 	log_session(log_info2, sess, "sending ICRQ\n");
 
 	pack = l2tp_packet_alloc(2, Message_Type_Incoming_Call_Request,
-				 &sess->paren_conn->peer_addr);
+				 &sess->paren_conn->peer_addr, sess->hide_avps,
+				 conf_secret, conf_secret_len);
 	if (pack == NULL) {
 		log_session(log_error, sess, "impossible to send ICRQ:"
 			    " packet allocation failed\n");
@@ -1712,7 +1726,8 @@ static int l2tp_send_ICRP(struct l2tp_sess_t *sess)
 	log_session(log_info2, sess, "sending ICRP\n");
 
 	pack = l2tp_packet_alloc(2, Message_Type_Incoming_Call_Reply,
-				 &sess->paren_conn->peer_addr);
+				 &sess->paren_conn->peer_addr, sess->hide_avps,
+				 conf_secret, conf_secret_len);
 	if (!pack) {
 		log_session(log_error, sess, "impossible to send ICRP:"
 			    " packet allocation failed\n");
@@ -1746,7 +1761,8 @@ static int l2tp_send_ICCN(struct l2tp_sess_t *sess)
 	log_session(log_info2, sess, "sending ICCN\n");
 
 	pack = l2tp_packet_alloc(2, Message_Type_Incoming_Call_Connected,
-				 &sess->paren_conn->peer_addr);
+				 &sess->paren_conn->peer_addr, sess->hide_avps,
+				 conf_secret, conf_secret_len);
 	if (pack == 0) {
 		log_session(log_error, sess, "impossible to send ICCN:"
 			    " packet allocation failed\n");
@@ -1790,7 +1806,8 @@ static int l2tp_send_OCRQ(struct l2tp_sess_t *sess)
 	log_session(log_info2, sess, "sending OCRQ\n");
 
 	pack = l2tp_packet_alloc(2, Message_Type_Outgoing_Call_Request,
-				 &sess->paren_conn->peer_addr);
+				 &sess->paren_conn->peer_addr, sess->hide_avps,
+				 conf_secret, conf_secret_len);
 	if (!pack) {
 		log_session(log_error, sess, "impossible to send OCRQ:"
 			    " packet allocation failed\n");
@@ -1854,7 +1871,8 @@ static int l2tp_send_OCRP(struct l2tp_sess_t *sess)
 	log_session(log_info2, sess, "sending OCRP\n");
 
 	pack = l2tp_packet_alloc(2, Message_Type_Outgoing_Call_Reply,
-				 &sess->paren_conn->peer_addr);
+				 &sess->paren_conn->peer_addr, sess->hide_avps,
+				 conf_secret, conf_secret_len);
 	if (pack == NULL) {
 		log_session(log_error, sess, "impossible to send OCRP:"
 			    " packet allocation failed\n");
@@ -1888,7 +1906,8 @@ static int l2tp_send_OCCN(struct l2tp_sess_t *sess)
 	log_session(log_info2, sess, "sending OCCN\n");
 
 	pack = l2tp_packet_alloc(2, Message_Type_Outgoing_Call_Connected,
-				 &sess->paren_conn->peer_addr);
+				 &sess->paren_conn->peer_addr, sess->hide_avps,
+				 conf_secret, conf_secret_len);
 	if (pack == NULL) {
 		log_session(log_error, sess, "impossible to send OCCN:"
 			    " packet allocation failed\n");
@@ -2008,7 +2027,8 @@ static int l2tp_recv_SCCRQ(const struct l2tp_serv_t *serv,
 		host_addr.sin_port = 0;
 
 		conn = l2tp_tunnel_alloc(&pack->addr, &host_addr,
-					 framing_cap->val.uint32, 1, 1);
+					 framing_cap->val.uint32, 1, 1,
+					 conf_hide_avps);
 		if (conn == NULL) {
 			log_error("l2tp: impossible to handle SCCRQ from %s:"
 				  " tunnel allocation failed\n", src_addr);
@@ -3533,6 +3553,7 @@ static int l2tp_create_tunnel_exec(const char *cmd, char * const *fields,
 	int peer_indx = -1;
 	int host_indx = -1;
 	int lns_mode = 0;
+	int hide_avps = conf_hide_avps;
 	uint16_t tid;
 	int indx;
 
@@ -3575,6 +3596,9 @@ static int l2tp_create_tunnel_exec(const char *cmd, char * const *fields,
 					  fields[indx]);
 				return CLI_CMD_INVAL;
 			}
+		} else if (strcmp("hide-avps", fields[indx]) == 0) {
+			++indx;
+			hide_avps = atoi(fields[indx]) > 0;
 		} else {
 			cli_sendv(client, "invalid option: \"%s\"\r\n",
 				  fields[indx]);
@@ -3598,7 +3622,7 @@ static int l2tp_create_tunnel_exec(const char *cmd, char * const *fields,
 		return CLI_CMD_INVAL;
 	}
 
-	conn = l2tp_tunnel_alloc(&peer, &host, 3, lns_mode, 0);
+	conn = l2tp_tunnel_alloc(&peer, &host, 3, lns_mode, 0, hide_avps);
 	if (conn == NULL) {
 		cli_send(client, "tunnel allocation failed\r\n");
 		return CLI_CMD_FAILED;
@@ -3668,7 +3692,7 @@ static void l2tp_create_tunnel_help(char * const *fields, int fields_cnt,
 {
 	cli_send(client,
 		 "l2tp create tunnel peer-addr <ip_addr> [host-addr <ip_addr>]"
-		 " [mode <lac|lns>]"
+		 " [hide-avps <0|1>] [mode <lac|lns>]"
 		 " - initiate new tunnel to peer\r\n");
 }
 
@@ -3694,6 +3718,10 @@ static void load_config(void)
 	if (opt && atoi(opt) >= 0)
 		conf_verbose = atoi(opt) > 0;
 
+	opt = conf_get_opt("l2tp", "hide-avps");
+	if (opt && atoi(opt) >= 0)
+		conf_hide_avps = atoi(opt) > 0;
+
 	opt = conf_get_opt("l2tp", "avp_permissive");
 	if (opt && atoi(opt) >= 0)
 		conf_avp_permissive = atoi(opt) > 0;
diff --git a/accel-pppd/ctrl/l2tp/l2tp.h b/accel-pppd/ctrl/l2tp/l2tp.h
index 82dafd7..566212a 100644
--- a/accel-pppd/ctrl/l2tp/l2tp.h
+++ b/accel-pppd/ctrl/l2tp/l2tp.h
@@ -63,6 +63,10 @@ struct l2tp_packet_t
 	struct sockaddr_in addr;
 	struct l2tp_hdr_t hdr;
 	struct list_head attrs;
+	struct l2tp_attr_t *last_RV;
+	const char *secret;
+	size_t secret_len;
+	int hide_avps;
 };
 
 extern int conf_verbose;
@@ -79,7 +83,8 @@ void l2tp_packet_free(struct l2tp_packet_t *);
 void l2tp_packet_print(const struct l2tp_packet_t *,
 		       void (*print)(const char *fmt, ...));
 struct l2tp_packet_t *l2tp_packet_alloc(int ver, int msg_type,
-					const struct sockaddr_in *addr);
+					const struct sockaddr_in *addr, int H,
+					const char *secret, size_t secret_len);
 int l2tp_packet_send(int sock, struct l2tp_packet_t *);
 int l2tp_packet_add_int16(struct l2tp_packet_t *pack, int id, int16_t val, int M);
 int l2tp_packet_add_int32(struct l2tp_packet_t *pack, int id, int32_t val, int M);
diff --git a/accel-pppd/ctrl/l2tp/packet.c b/accel-pppd/ctrl/l2tp/packet.c
index 5a40840..9bd11eb 100644
--- a/accel-pppd/ctrl/l2tp/packet.c
+++ b/accel-pppd/ctrl/l2tp/packet.c
@@ -13,6 +13,7 @@
 #include "log.h"
 #include "mempool.h"
 #include "memdebug.h"
+#include "utils.h"
 
 #include "l2tp.h"
 #include "attr_defs.h"
@@ -40,6 +41,8 @@ void l2tp_packet_print(const struct l2tp_packet_t *pack,
 		val = l2tp_dict_find_value(attr->attr, attr->val);
 		if (val)
 			print(" %s", val->name);
+		else if (attr->H)
+			print(" (hidden, %hu bytes)", attr->length);
 		else {
 			switch (attr->attr->type) {
 				case ATTR_TYPE_INT16:
@@ -60,7 +63,8 @@ void l2tp_packet_print(const struct l2tp_packet_t *pack,
 }
 
 struct l2tp_packet_t *l2tp_packet_alloc(int ver, int msg_type,
-					const struct sockaddr_in *addr)
+					const struct sockaddr_in *addr, int H,
+					const char *secret, size_t secret_len)
 {
 	struct l2tp_packet_t *pack = mempool_alloc(pack_pool);
 	if (!pack)
@@ -73,6 +77,9 @@ struct l2tp_packet_t *l2tp_packet_alloc(int ver, int msg_type,
 	pack->hdr.L = 1;
 	pack->hdr.S = 1;
 	memcpy(&pack->addr, addr, sizeof(*addr));
+	pack->hide_avps = H;
+	pack->secret = secret;
+	pack->secret_len = secret_len;
 
 	if (msg_type) {
 		if (l2tp_packet_add_int16(pack, Message_Type, msg_type, 1)) {
@@ -90,7 +97,8 @@ void l2tp_packet_free(struct l2tp_packet_t *pack)
 
 	while (!list_empty(&pack->attrs)) {
 		attr = list_entry(pack->attrs.next, typeof(*attr), entry);
-		if (attr->attr->type == ATTR_TYPE_OCTETS || attr->attr->type == ATTR_TYPE_STRING)
+		if (attr->H || attr->attr->type == ATTR_TYPE_OCTETS
+		    || attr->attr->type == ATTR_TYPE_STRING)
 			_free(attr->val.octets);
 		list_del(&attr->entry);
 		mempool_free(attr);
@@ -493,7 +501,10 @@ int l2tp_packet_send(int sock, struct l2tp_packet_t *pack)
 		avp->H = attr->H;
 		avp->length = sizeof(*avp) + attr->length;
 		*(uint16_t *)ptr = htons(*(uint16_t *)ptr);
-		switch (attr->attr->type) {
+		if (attr->H)
+			memcpy(avp->val, attr->val.octets, attr->length);
+		else
+			switch (attr->attr->type) {
 			case ATTR_TYPE_INT16:
 				*(int16_t *)avp->val = htons(attr->val.int16);
 				break;
@@ -504,8 +515,7 @@ int l2tp_packet_send(int sock, struct l2tp_packet_t *pack)
 			case ATTR_TYPE_OCTETS:
 				memcpy(avp->val, attr->val.string, attr->length);
 				break;
-		}
-
+			}
 		ptr += sizeof(*avp) + attr->length;
 		len += sizeof(*avp) + attr->length;
 	}
@@ -536,7 +546,120 @@ int l2tp_packet_send(int sock, struct l2tp_packet_t *pack)
 	return 0;
 }
 
-static struct l2tp_attr_t *attr_alloc(int id, int M)
+int encode_attr(const struct l2tp_packet_t *pack, struct l2tp_attr_t *attr,
+		const void *val, uint16_t val_len)
+{
+	uint8_t *u8_ptr = NULL;
+	uint8_t md5[MD5_DIGEST_LENGTH];
+	MD5_CTX md5_ctx;
+	uint16_t pad_len;
+	uint16_t attr_type;
+	uint16_t blocks_left;
+	uint16_t last_block_len;
+	int err;
+
+	if (pack->secret == NULL || pack->secret_len == 0) {
+		log_error("l2tp: impossible to hide AVP: no secret\n");
+		goto err;
+	}
+	if (pack->last_RV == NULL) {
+		log_error("l2tp: impossible to hide AVP: no random vector\n");
+		goto err;
+	}
+
+	if (u_randbuf(&pad_len, sizeof(pad_len), &err) < 0) {
+		if (err)
+			log_error("l2tp: impossible to hide AVP:"
+				  " reading from urandom failed: %s\n",
+				  strerror(err));
+		else
+			log_error("l2tp: impossible to hide AVP:"
+				  " end of file reached while reading"
+				  " from urandom\n");
+		goto err;
+	}
+	/* Use at least 16 bytes of padding */
+	pad_len = (pad_len & 0x007F) + 16;
+
+	/* Generate Hidden AVP Subformat:
+	 *   -original AVP size (2 bytes, network byte order)
+	 *   -original AVP value ('val_len' bytes)
+	 *   -padding ('pad_len' bytes of random values)
+	 */
+	attr->length = sizeof(val_len) + val_len + pad_len;
+	attr->val.octets = _malloc(attr->length);
+	if (attr->val.octets == NULL) {
+		log_error("l2tp: impossible to hide AVP:"
+			  " memory allocation failed\n");
+		goto err;
+	}
+
+	*(uint16_t *)attr->val.octets = htons(val_len);
+	memcpy(attr->val.octets + sizeof(val_len), val, val_len);
+
+	if (u_randbuf(attr->val.octets + sizeof(val_len) + val_len,
+		      pad_len, &err) < 0) {
+		if (err)
+			log_error("l2tp: impossible to hide AVP:"
+				  " reading from urandom failed: %s\n",
+				  strerror(err));
+		else
+			log_error("l2tp: impossible to hide AVP:"
+				  " end of file reached while reading"
+				  " from urandom\n");
+		goto err_free;
+	}
+
+	/* Hidden AVP cipher:
+	 * ciphered[0] = clear[0] xor MD5(attr_type, secret, RV)
+	 * ciphered[1] = clear[1] xor MD5(secret, ciphered[0])
+	 * ...
+	 * ciphered[n] = clear[n] xor MD5(secret, ciphered[n-1])
+	 */
+	attr_type = htons(attr->attr->id);
+	MD5_Init(&md5_ctx);
+	MD5_Update(&md5_ctx, &attr_type, sizeof(attr_type));
+	MD5_Update(&md5_ctx, pack->secret, pack->secret_len);
+	MD5_Update(&md5_ctx, pack->last_RV->val.octets, pack->last_RV->length);
+	MD5_Final(md5, &md5_ctx);
+
+	if (attr->length <= MD5_DIGEST_LENGTH) {
+		memxor(attr->val.octets, md5, attr->length);
+		return 0;
+	}
+
+	memxor(attr->val.octets, md5, MD5_DIGEST_LENGTH);
+
+	blocks_left = attr->length / MD5_DIGEST_LENGTH - 1;
+	last_block_len = attr->length % MD5_DIGEST_LENGTH;
+
+	for (u8_ptr = attr->val.octets; blocks_left; --blocks_left) {
+		MD5_Init(&md5_ctx);
+		MD5_Update(&md5_ctx, pack->secret, pack->secret_len);
+		MD5_Update(&md5_ctx, u8_ptr, MD5_DIGEST_LENGTH);
+		MD5_Final(md5, &md5_ctx);
+		u8_ptr += MD5_DIGEST_LENGTH;
+		memxor(u8_ptr, md5, MD5_DIGEST_LENGTH);
+	}
+
+	if (last_block_len) {
+		MD5_Init(&md5_ctx);
+		MD5_Update(&md5_ctx, pack->secret, pack->secret_len);
+		MD5_Update(&md5_ctx, u8_ptr, MD5_DIGEST_LENGTH);
+		MD5_Final(md5, &md5_ctx);
+		memxor(u8_ptr + MD5_DIGEST_LENGTH, md5, last_block_len);
+	}
+
+	return 0;
+
+err_free:
+	_free(attr->val.octets);
+	attr->val.octets = NULL;
+err:
+	return -1;
+}
+
+static struct l2tp_attr_t *attr_alloc(int id, int M, int H)
 {
 	struct l2tp_attr_t *attr;
 	struct l2tp_dict_attr_t *da;
@@ -560,75 +683,183 @@ static struct l2tp_attr_t *attr_alloc(int id, int M)
 	else
 		attr->M = M;
 
-	//if (da->H != -1)
-	//attr->H = da->H;
+	if (da->H != -1)
+		attr->H = da->H;
+	else
+		attr->H = H;
 
 	return attr;
 }
 
+static int l2tp_packet_add_random_vector(struct l2tp_packet_t *pack)
+{
+	struct l2tp_attr_t *attr = attr_alloc(Random_Vector, 1, 0);
+	uint16_t ranvec_len;
+	int err;
+
+	if (!attr)
+		goto err;
+
+	if (u_randbuf(&ranvec_len, sizeof(ranvec_len), &err) < 0) {
+		if (err)
+			log_error("l2tp: impossible to build Random Vector:"
+				  " reading from urandom failed: %s\n",
+				  strerror(err));
+		else
+			log_error("l2tp: impossible to build Random Vector:"
+				  " end of file reached while reading"
+				  " from urandom\n");
+		goto err_attr;
+	}
+	/* RFC 2661 recommends that Random Vector be least 16 bytes long */
+	ranvec_len = (ranvec_len & 0x007F) + 16;
+
+	attr->length = ranvec_len;
+	attr->val.octets = _malloc(ranvec_len);
+	if (!attr->val.octets) {
+		log_emerg("l2tp: out of memory\n");
+		goto err_attr;
+	}
+
+	if (u_randbuf(attr->val.octets, ranvec_len, &err) < 0) {
+		if (err)
+			log_error("l2tp: impossible to build Random Vector:"
+				  " reading from urandom failed: %s\n",
+				  strerror(err));
+		else
+			log_error("l2tp: impossible to build Random Vector:"
+				  " end of file reached while reading"
+				  " from urandom\n");
+		goto err_attr_val;
+	}
+
+	list_add_tail(&attr->entry, &pack->attrs);
+	pack->last_RV = attr;
+
+	return 0;
+
+err_attr_val:
+	_free(attr->val.octets);
+err_attr:
+	mempool_free(attr);
+err:
+	return -1;
+}
+
 int l2tp_packet_add_int16(struct l2tp_packet_t *pack, int id, int16_t val, int M)
 {
-	struct l2tp_attr_t *attr = attr_alloc(id, M);
+	struct l2tp_attr_t *attr = attr_alloc(id, M, pack->hide_avps);
 
 	if (!attr)
 		return -1;
 
-	attr->length = 2;
-	attr->val.int16 = val;
+	if (attr->H) {
+		if (pack->last_RV == NULL)
+			if (l2tp_packet_add_random_vector(pack) < 0)
+				goto err;
+		val = htons(val);
+		if (encode_attr(pack, attr, &val, sizeof(val)) < 0)
+			goto err;
+	} else {
+		attr->length = sizeof(val);
+		attr->val.int16 = val;
+	}
 	list_add_tail(&attr->entry, &pack->attrs);
 
 	return 0;
+
+err:
+	mempool_free(attr);
+	return -1;
 }
+
 int l2tp_packet_add_int32(struct l2tp_packet_t *pack, int id, int32_t val, int M)
 {
-	struct l2tp_attr_t *attr = attr_alloc(id, M);
+	struct l2tp_attr_t *attr = attr_alloc(id, M, pack->hide_avps);
 
 	if (!attr)
 		return -1;
 
-	attr->length = 4;
-	attr->val.int32 = val;
+	if (attr->H) {
+		if (pack->last_RV == NULL)
+			if (l2tp_packet_add_random_vector(pack) < 0)
+				goto err;
+		val = htonl(val);
+		if (encode_attr(pack, attr, &val, sizeof(val)) < 0)
+			goto err;
+	} else {
+		attr->length = sizeof(val);
+		attr->val.int32 = val;
+	}
 	list_add_tail(&attr->entry, &pack->attrs);
 
 	return 0;
+
+err:
+	mempool_free(attr);
+	return -1;
 }
+
 int l2tp_packet_add_string(struct l2tp_packet_t *pack, int id, const char *val, int M)
 {
-	struct l2tp_attr_t *attr = attr_alloc(id, M);
+	struct l2tp_attr_t *attr = attr_alloc(id, M, pack->hide_avps);
+	size_t val_len = strlen(val);
 
 	if (!attr)
 		return -1;
 
-	attr->length = strlen(val);
-	attr->val.string = _strdup(val);
-	if (!attr->val.string) {
-		log_emerg("l2tp: out of memory\n");
-		mempool_free(attr);
-		return -1;
+	if (attr->H) {
+		if (pack->last_RV == NULL)
+			if (l2tp_packet_add_random_vector(pack) < 0)
+				goto err;
+		if (encode_attr(pack, attr, val, val_len) < 0)
+			goto err;
+	} else {
+		attr->length = val_len;
+		attr->val.string = _strdup(val);
+		if (!attr->val.string) {
+			log_emerg("l2tp: out of memory\n");
+			goto err;
+		}
 	}
 	list_add_tail(&attr->entry, &pack->attrs);
 
 	return 0;
+
+err:
+	mempool_free(attr);
+	return -1;
 }
 
 int l2tp_packet_add_octets(struct l2tp_packet_t *pack, int id, const uint8_t *val, int size, int M)
 {
-	struct l2tp_attr_t *attr = attr_alloc(id, M);
+	struct l2tp_attr_t *attr = attr_alloc(id, M, pack->hide_avps);
 
 	if (!attr)
 		return -1;
 
-	attr->length = size;
-	attr->val.octets = _malloc(size);
-	if (!attr->val.octets) {
-		log_emerg("l2tp: out of memory\n");
-		mempool_free(attr);
-		return -1;
+	if (attr->H) {
+		if (pack->last_RV == NULL)
+			if (l2tp_packet_add_random_vector(pack) < 0)
+				goto err;
+		if (encode_attr(pack, attr, val, size) < 0)
+			goto err;
+	} else {
+		attr->length = size;
+		attr->val.octets = _malloc(size);
+		if (!attr->val.octets) {
+			log_emerg("l2tp: out of memory\n");
+			goto err;
+		}
+		memcpy(attr->val.octets, val, attr->length);
 	}
-	memcpy(attr->val.octets, val, attr->length);
 	list_add_tail(&attr->entry, &pack->attrs);
 
 	return 0;
+
+err:
+	mempool_free(attr);
+	return -1;
 }
 
 static void init(void)