1 package edu.uci.iotproject.detection.layer2;
3 import edu.uci.iotproject.analysis.TriggerTrafficExtractor;
4 import edu.uci.iotproject.util.PcapPacketUtils;
5 import org.pcap4j.core.PcapPacket;
6 import org.pcap4j.util.MacAddress;
8 import java.util.ArrayList;
12 * Attempts to detect the presence of a specific packet sequence in the set of packets provided through multiple calls
13 * to {@link #matchPacket(PcapPacket)}, considering only layer 2 information.
15 * @author Janus Varmarken {@literal <jvarmark@uci.edu>}
16 * @author Rahmadi Trimananda {@literal <rtrimana@uci.edu>}
18 public class Layer2SequenceMatcher {
21 * The sequence this {@link Layer2SequenceMatcher} is searching for.
23 private final List<PcapPacket> mSequence;
26 * Buffer of actual packets seen so far that match the searched sequence (i.e., constitutes a subsequence of the
29 private final List<PcapPacket> mMatchedPackets = new ArrayList<>();
32 * Models the directions of packets in {@link #mSequence}. As the sequence matcher assumes that it is only presented
33 * with packet from a single flow (packets exchanged between two devices), we can model the packet directions with a
34 * single bit. We don't have any notion "phone to device" or "device to phone" as we don't know the MAC addresses
35 * of devices in advance during matching.
37 private final boolean[] mPacketDirections;
40 * Create a {@code Layer2SequenceMatcher}.
41 * @param sequence The sequence to match against (search for).
43 public Layer2SequenceMatcher(List<PcapPacket> sequence) {
45 // Compute packet directions for sequence.
46 mPacketDirections = new boolean[sequence.size()];
47 for (int i = 0; i < sequence.size(); i++) {
49 // No previous packet; boolean parameter is ignored in this special case.
50 mPacketDirections[i] = getPacketDirection(null, true, sequence.get(i));
52 // Base direction marker on direction of previous packet.
53 PcapPacket prevPkt = mSequence.get(i-1);
54 boolean prevPktDirection = mPacketDirections[i-1];
55 mPacketDirections[i] = getPacketDirection(prevPkt, prevPktDirection, sequence.get(i));
61 * Attempt to advance this {@code Layer2SequenceMatcher} by matching {@code packet} against the packet that this
62 * {@code Layer2SequenceMatcher} expects as the next packet of the sequence it is searching for.
64 * @return {@code true} if this {@code Layer2SequenceMatcher} could advance by adding {@code packet} to its set of
65 * matched packets, {@code false} otherwise.
67 public boolean matchPacket(PcapPacket packet) {
68 if (getMatchedPacketsCount() == getTargetSequencePacketCount()) {
69 // We already matched the entire sequence, so we can't match any more packets.
73 // Verify that new packet pertains to same flow as previously matched packets, if any.
74 if (getMatchedPacketsCount() > 0) {
75 MacAddress pktSrc = PcapPacketUtils.getEthSrcAddr(packet);
76 MacAddress pktDst = PcapPacketUtils.getEthDstAddr(packet);
77 MacAddress earlierPktSrc = PcapPacketUtils.getEthSrcAddr(mMatchedPackets.get(0));
78 MacAddress earlierPktDst = PcapPacketUtils.getEthDstAddr(mMatchedPackets.get(0));
79 if (!(pktSrc.equals(earlierPktSrc) && pktDst.equals(earlierPktDst) ||
80 pktSrc.equals(earlierPktDst) && pktDst.equals(earlierPktSrc))) {
85 // Get representative of the packet we expect to match next.
86 PcapPacket expected = mSequence.get(mMatchedPackets.size());
87 // First verify if the received packet has the length we're looking for.
88 if (packet.getOriginalLength() == expected.getOriginalLength()) {
89 // If this is the first packet, we only need to verify that its length is correct. Time constraints are
90 // obviously satisfied as there are no previous packets. Furthermore, direction matches by definition as we
91 // don't know the MAC of the device (or phone) in advance, so we can't enforce a rule saying "first packet
92 // must originate from this particular MAC".
93 if (getMatchedPacketsCount() == 0) {
94 // Store packet as matched and advance.
95 mMatchedPackets.add(packet);
98 // Check if direction of packet matches expected direction.
99 boolean actualDirection = getPacketDirection(mMatchedPackets.get(getMatchedPacketsCount()-1),
100 mPacketDirections[getMatchedPacketsCount()-1], packet);
101 boolean expectedDirection = mPacketDirections[getMatchedPacketsCount()];
102 if (actualDirection != expectedDirection) {
105 // Next apply timing constraints:
106 // 1: to be a match, the packet must have a later timestamp than any other packet currently matched
107 // 2: does adding the packet cause the max allowed time between first packet and last packet to be exceeded?
108 if (!packet.getTimestamp().isAfter(mMatchedPackets.get(getMatchedPacketsCount()-1).getTimestamp())) {
111 if (packet.getTimestamp().isAfter(mMatchedPackets.get(0).getTimestamp().
112 plusMillis(TriggerTrafficExtractor.INCLUSION_WINDOW_MILLIS))) {
115 // If we made it here, it means that this packet has the expected length, direction, and obeys the timing
116 // constraints, so we store it and advance.
117 mMatchedPackets.add(packet);
118 if (mMatchedPackets.size() == mSequence.size()) {
119 // TODO report (to observers?) that we are done?
126 public int getMatchedPacketsCount() {
127 return mMatchedPackets.size();
130 public int getTargetSequencePacketCount() {
131 return mSequence.size();
134 public List<PcapPacket> getTargetSequence() {
138 public List<PcapPacket> getMatchedPackets() {
139 return mMatchedPackets;
143 * Utility for {@code getMatchedPackets().get(getMatchedPackets().size()-1)}.
144 * @return The last matched packet, or {@code null} if no packets have been matched yet.
146 public PcapPacket getLastPacket() {
147 return mSequence.size() > 0 ? mSequence.get(mSequence.size()-1) : null;
151 * Compute the direction of a packet based on the previous packet. If no previous packet is provided, the direction
152 * of {@code currPkt} is {@code true} by definition.
153 * @param prevPkt The previous packet, if any.
154 * @param prevPktDirection The computed direction of the previous packet
155 * @param currPkt The current packet for which the direction is to be determined.
156 * @return The direction of {@code currPkt}.
158 private boolean getPacketDirection(PcapPacket prevPkt, boolean prevPktDirection, PcapPacket currPkt) {
159 if (prevPkt == null) {
160 // By definition, use true as direction marker for first packet
163 if (PcapPacketUtils.getEthSrcAddr(prevPkt).equals(PcapPacketUtils.getEthSrcAddr(currPkt))) {
164 // Current packet goes in same direction as previous packet.
165 return prevPktDirection;
167 // Current packet goes in opposite direction of previous packet.
168 return !prevPktDirection;