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/*
* openvpn.c
*
* Copyright (C) 2011-16 - ntop.org
*
* OpenVPN TCP / UDP Detection - 128/160 hmac
*
* Detection based upon these openvpn protocol properties:
* - opcode
* - packet ID
* - session ID
*
* Two (good) packets are needed to perform detection.
* - First packet from client: save session ID
* - Second packet from server: report saved session ID
*
* TODO
* - Support PSK only mode (instead of TLS)
* - Support PSK + TLS mode (PSK used for early authentication)
* - TLS certificate extraction
*
*/
#include "ndpi_api.h"
#ifdef NDPI_PROTOCOL_OPENVPN
#define P_CONTROL_HARD_RESET_CLIENT_V1 (0x01 << 3)
#define P_CONTROL_HARD_RESET_CLIENT_V2 (0x07 << 3)
#define P_CONTROL_HARD_RESET_SERVER_V1 (0x02 << 3)
#define P_CONTROL_HARD_RESET_SERVER_V2 (0x08 << 3)
#define P_OPCODE_MASK 0xF8
#define P_SHA1_HMAC_SIZE 20
#define P_HMAC_128 16 // (RSA-)MD5, (RSA-)MD4, ..others
#define P_HMAC_160 20 // (RSA-|DSA-)SHA(1), ..others, SHA1 is openvpn default
#define P_HARD_RESET_PACKET_ID_OFFSET(hmac_size) (9 + hmac_size)
#define P_PACKET_ID_ARRAY_LEN_OFFSET(hmac_size) (P_HARD_RESET_PACKET_ID_OFFSET(hmac_size) + 8)
static inline u_int32_t get_packet_id(const u_int8_t * payload, u_int8_t hms) {
return be32toh(*(u_int32_t*)(payload + P_HARD_RESET_PACKET_ID_OFFSET(hms)));
}
static inline int8_t check_pkid_and_detect_hmac_size(const u_int8_t * payload) {
// try to guess
if (get_packet_id(payload, P_HMAC_160) == 1)
return P_HMAC_160;
if (get_packet_id(payload, P_HMAC_128) == 1)
return P_HMAC_128;
return -1;
}
void ndpi_search_openvpn(struct ndpi_detection_module_struct* ndpi_struct,
struct ndpi_flow_struct* flow) {
struct ndpi_packet_struct* packet = &flow->packet;
const u_int8_t * ovpn_payload = packet->payload;
const u_int8_t * session_remote;
u_int8_t opcode;
u_int8_t alen;
int8_t hmac_size;
if (packet->payload_packet_len >= 40) {
// skip openvpn TCP transport packet size
if (packet->tcp != NULL)
ovpn_payload += 2;
opcode = ovpn_payload[0] & P_OPCODE_MASK;
if (flow->ovpn_counter == 0 && (opcode == P_CONTROL_HARD_RESET_CLIENT_V1 ||
opcode == P_CONTROL_HARD_RESET_CLIENT_V2)) {
if (check_pkid_and_detect_hmac_size(ovpn_payload) > 0) {
memcpy(flow->ovpn_session_id, ovpn_payload+1, 8);
NDPI_LOG(NDPI_PROTOCOL_OPENVPN, ndpi_struct, NDPI_LOG_DEBUG,
"session key: %02x%02x%02x%02x%02x%02x%02x%02x\n",
flow->ovpn_session_id[0], flow->ovpn_session_id[1], flow->ovpn_session_id[2], flow->ovpn_session_id[3],
flow->ovpn_session_id[4], flow->ovpn_session_id[5], flow->ovpn_session_id[6], flow->ovpn_session_id[7]);
}
} else if (flow->ovpn_counter == 1 && (opcode == P_CONTROL_HARD_RESET_SERVER_V1 ||
opcode == P_CONTROL_HARD_RESET_SERVER_V2)) {
hmac_size = check_pkid_and_detect_hmac_size(ovpn_payload);
if (hmac_size > 0) {
alen = ovpn_payload[P_PACKET_ID_ARRAY_LEN_OFFSET(hmac_size)];
session_remote = ovpn_payload + P_PACKET_ID_ARRAY_LEN_OFFSET(hmac_size) + 1 + alen * 4;
if (memcmp(flow->ovpn_session_id, session_remote, 8) == 0)
ndpi_set_detected_protocol(ndpi_struct, flow, NDPI_PROTOCOL_OPENVPN, NDPI_PROTOCOL_UNKNOWN);
else
NDPI_LOG(NDPI_PROTOCOL_OPENVPN, ndpi_struct, NDPI_LOG_DEBUG,
"key mismatch: %02x%02x%02x%02x%02x%02x%02x%02x\n",
session_remote[0], session_remote[1], session_remote[2], session_remote[3],
session_remote[4], session_remote[5], session_remote[6], session_remote[7]);
}
} else if (flow->ovpn_counter >= 2)
NDPI_ADD_PROTOCOL_TO_BITMASK(flow->excluded_protocol_bitmask, NDPI_PROTOCOL_OPENVPN);
flow->ovpn_counter++;
}
}
void init_openvpn_dissector(struct ndpi_detection_module_struct *ndpi_struct, u_int32_t *id, NDPI_PROTOCOL_BITMASK *detection_bitmask)
{
ndpi_set_bitmask_protocol_detection("OpenVPN", ndpi_struct, detection_bitmask, *id,
NDPI_PROTOCOL_OPENVPN,
ndpi_search_openvpn,
NDPI_SELECTION_BITMASK_PROTOCOL_TCP_OR_UDP_WITH_PAYLOAD,
SAVE_DETECTION_BITMASK_AS_UNKNOWN,
ADD_TO_DETECTION_BITMASK);
*id += 1;
}
#endif
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