/*
 * kerberos.c
 *
 * Copyright (C) 2011-19 - ntop.org
 * Copyright (C) 2009-2011 by ipoque GmbH
 *
 * This file is part of nDPI, an open source deep packet inspection
 * library based on the OpenDPI and PACE technology by ipoque GmbH
 *
 * nDPI is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * nDPI is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with nDPI.  If not, see <http://www.gnu.org/licenses/>.
 *
 */

#include "ndpi_protocol_ids.h"

#define NDPI_CURRENT_PROTO NDPI_PROTOCOL_KERBEROS

#include "ndpi_api.h"

// #define KERBEROS_DEBUG 1

static void ndpi_int_kerberos_add_connection(struct ndpi_detection_module_struct *ndpi_struct,
					     struct ndpi_flow_struct *flow) {
  ndpi_set_detected_protocol(ndpi_struct, flow, NDPI_PROTOCOL_KERBEROS, NDPI_PROTOCOL_UNKNOWN);
  NDPI_LOG_DBG(ndpi_struct, "trace KERBEROS\n");
}


void ndpi_search_kerberos(struct ndpi_detection_module_struct *ndpi_struct,
			  struct ndpi_flow_struct *flow) {
  struct ndpi_packet_struct *packet = &flow->packet;

  NDPI_LOG_DBG(ndpi_struct, "search KERBEROS\n");

  /* I have observed 0a,0c,0d,0e at packet->payload[19/21], maybe there are other possibilities */
  if(packet->payload_packet_len >= 4 && ntohl(get_u_int32_t(packet->payload, 0)) == packet->payload_packet_len - 4) {
    if(packet->payload_packet_len > 19 &&
	packet->payload[14] == 0x05 &&
	(packet->payload[19] == 0x0a ||
	 packet->payload[19] == 0x0c || packet->payload[19] == 0x0d || packet->payload[19] == 0x0e)) {
      if(packet->payload[19] == 0x0a) /* AS-REQ */ {
	u_int pad_data_len = packet->payload[23];
	u_int body_offset  = pad_data_len + 23;

	if(body_offset < packet->payload_packet_len) {
	  u_int name_offset = body_offset + 30;

	  if(name_offset < packet->payload_packet_len) {
	    u_int cname_len = packet->payload[name_offset];

	    if((cname_len+name_offset) < packet->payload_packet_len) {
	      u_int realm_len, realm_offset = cname_len + name_offset + 4, i;
	      char cname_str[24];

	      if(cname_len >= sizeof(cname_str))
		cname_len = sizeof(cname_str);

	      strncpy(cname_str, (char*)&packet->payload[name_offset+1], cname_len);
	      cname_str[cname_len] = '\0';
	      for(i=0; i<cname_len; i++) cname_str[i] = tolower(cname_str[i]);
	      
#ifdef KERBEROS_DEBUG
	      printf("[Kerberos Cname][len: %u][%s]\n", cname_len, cname_str);
#endif

	      snprintf(flow->protos.kerberos.cname, sizeof(flow->protos.kerberos.cname), "%s", cname_str);
	      
	      realm_len = packet->payload[realm_offset];

	      if((realm_offset+realm_len) < packet->payload_packet_len) {
		char realm_str[24];

		if(realm_len >= sizeof(realm_str))
		  realm_len = sizeof(realm_str);

		strncpy(realm_str, (char*)&packet->payload[realm_offset+1], realm_len);
		realm_str[realm_len] = '\0';
		for(i=0; i<realm_len; i++) realm_str[i] = tolower(realm_str[i]);


#ifdef KERBEROS_DEBUG
		printf("[Kerberos Realm][len: %u][%s]\n", realm_len, realm_str);
#endif
		snprintf(flow->protos.kerberos.realm, sizeof(flow->protos.kerberos.realm), "%s", realm_str);
	      }
	    }
	  }
	}
      }

      ndpi_int_kerberos_add_connection(ndpi_struct, flow);
      return;

    }

    if(packet->payload_packet_len > 21 &&
	packet->payload[16] == 0x05 &&
	(packet->payload[21] == 0x0a ||
	 packet->payload[21] == 0x0c || packet->payload[21] == 0x0d || packet->payload[21] == 0x0e)) {
      ndpi_int_kerberos_add_connection(ndpi_struct, flow);
      return;

    }
  }

  NDPI_EXCLUDE_PROTO(ndpi_struct, flow);
}


void init_kerberos_dissector(struct ndpi_detection_module_struct *ndpi_struct,
			     u_int32_t *id, NDPI_PROTOCOL_BITMASK *detection_bitmask) {
  ndpi_set_bitmask_protocol_detection("Kerberos", ndpi_struct, detection_bitmask, *id,
				      NDPI_PROTOCOL_KERBEROS,
				      ndpi_search_kerberos,
				      NDPI_SELECTION_BITMASK_PROTOCOL_V4_V6_TCP_WITH_PAYLOAD_WITHOUT_RETRANSMISSION,
				      SAVE_DETECTION_BITMASK_AS_UNKNOWN,
				      ADD_TO_DETECTION_BITMASK);

  *id += 1;
}