1 package edu.uci.iotproject.detection.layer2;
3 import edu.uci.iotproject.analysis.TriggerTrafficExtractor;
4 import edu.uci.iotproject.analysis.UserAction;
5 import edu.uci.iotproject.detection.AbstractClusterMatcher;
6 import edu.uci.iotproject.detection.ClusterMatcherObserver;
7 import edu.uci.iotproject.detection.SignatureDetectorObserver;
8 import edu.uci.iotproject.io.PcapHandleReader;
9 import edu.uci.iotproject.io.PrintWriterUtils;
10 import edu.uci.iotproject.trafficreassembly.layer2.Layer2Flow;
11 import edu.uci.iotproject.trafficreassembly.layer2.Layer2FlowReassembler;
12 import edu.uci.iotproject.util.PcapPacketUtils;
13 import edu.uci.iotproject.util.PrintUtils;
14 import org.jgrapht.GraphPath;
15 import org.jgrapht.alg.shortestpath.DijkstraShortestPath;
16 import org.jgrapht.graph.DefaultWeightedEdge;
17 import org.jgrapht.graph.SimpleDirectedWeightedGraph;
18 import org.pcap4j.core.*;
21 import java.io.FileWriter;
22 import java.io.IOException;
23 import java.io.PrintWriter;
24 import java.time.Duration;
26 import java.util.function.Function;
27 import java.util.regex.Pattern;
30 * Performs layer 2 signature detection.
32 * @author Janus Varmarken {@literal <jvarmark@uci.edu>}
33 * @author Rahmadi Trimananda {@literal <rtrimana@uci.edu>}
35 public class Layer2SignatureDetector implements PacketListener, ClusterMatcherObserver {
38 * If set to {@code true}, output written to the results file is also dumped to standard out.
40 private static boolean DUPLICATE_OUTPUT_TO_STD_OUT = true;
44 * This is only useful for the filter for direction when it is a WAN signature (Phone-Cloud or Device-Cloud).
45 * Phone-Device signatures do not have router MAC address in it.
47 // TODO: MAKE THESE INPUT PARAMETERS
48 private static String TRAINING_ROUTER_WLAN_MAC = "b0:b9:8a:73:69:8e";
49 private static String ROUTER_WLAN_MAC = "00:c1:b1:14:eb:31";
50 //private static String TRAINING_ROUTER_WLAN_MAC = null;
51 //private static String ROUTER_WLAN_MAC = null;
53 private static List<Function<Layer2Flow, Boolean>> parseSignatureMacFilters(String filtersString) {
54 List<Function<Layer2Flow, Boolean>> filters = new ArrayList<>();
55 String[] filterRegexes = filtersString.split(";");
56 for (String filterRegex : filterRegexes) {
57 final Pattern regex = Pattern.compile(filterRegex);
58 // Create a filter that includes all flows where one of the two MAC addresses match the regex.
59 filters.add(flow -> regex.matcher(flow.getEndpoint1().toString()).matches() || regex.matcher(flow.getEndpoint2().toString()).matches());
64 public static void main(String[] args) throws PcapNativeException, NotOpenException, IOException {
65 // Parse required parameters.
66 if (args.length < 10) {
67 String errMsg = String.format("SPECTO version 1.0\n" +
68 "Copyright (C) 2018-2019 Janus Varmarken and Rahmadi Trimananda.\n" +
69 "University of California, Irvine.\n" +
70 "All rights reserved.\n\n" +
71 "Usage: %s inputPcapFile onAnalysisFile offAnalysisFile onSignatureFile offSignatureFile " +
72 "resultsFile signatureDuration eps onMaxSkippedPackets offMaxSkippedPackets" +
73 "\n inputPcapFile: the target of the detection" +
74 "\n onAnalysisFile: the file that contains the ON clusters analysis" +
75 "\n offAnalysisFile: the file that contains the OFF clusters analysis" +
76 "\n onSignatureFile: the file that contains the ON signature to search for" +
77 "\n offSignatureFile: the file that contains the OFF signature to search for" +
78 "\n resultsFile: where to write the results of the detection" +
79 "\n signatureDuration: the maximum duration of signature detection" +
80 "\n eps: the epsilon value for the DBSCAN algorithm" +
81 "\n onMaxSkippedPackets: the maximum duration of ON signature detection (put -1 if not used)" +
82 "\n offMaxSkippedPackets: the maximum duration of OFF signature detection (put -1 if not used)",
83 Layer2SignatureDetector.class.getSimpleName());
84 System.out.println(errMsg);
85 String optParamsExplained = "Above are the required, positional arguments. In addition to these, the " +
86 "following options and associated positional arguments may be used:\n" +
87 " '-onmacfilters <regex>;<regex>;...;<regex>' which specifies that sequence matching should ONLY" +
88 " be performed on flows where the MAC of one of the two endpoints matches the given regex. Note " +
89 "that you MUST specify a regex for each cluster of the signature. This is to facilitate more " +
90 "aggressive filtering on parts of the signature (e.g., the communication that involves the " +
91 "smart home device itself as one can drop all flows that do not include an endpoint with a MAC " +
92 "that matches the vendor's prefix).\n" +
93 " '-offmacfilters <regex>;<regex>;...;<regex>' works exactly the same as onmacfilters, but " +
94 "applies to the OFF signature instead of the ON signature.\n" +
95 " '-sout <boolean literal>' true/false literal indicating if output should also be printed to std out; default is true.";
96 System.out.println(optParamsExplained);
99 final String pcapFile = args[0];
100 final String onClusterAnalysisFile = args[1];
101 final String offClusterAnalysisFile = args[2];
102 final String onSignatureFile = args[3];
103 final String offSignatureFile = args[4];
104 final String resultsFile = args[5];
105 final int signatureDuration = Integer.parseInt(args[6]);
106 final double eps = Double.parseDouble(args[7]);
107 final int onMaxSkippedPackets = Integer.parseInt(args[8]);
108 final int offMaxSkippedPackets = Integer.parseInt(args[9]);
110 // Parse optional parameters.
111 List<Function<Layer2Flow, Boolean>> onSignatureMacFilters = null, offSignatureMacFilters = null;
112 final int optParamsStartIdx = 7;
113 if (args.length > optParamsStartIdx) {
114 for (int i = optParamsStartIdx; i < args.length; i++) {
115 if (args[i].equalsIgnoreCase("-onMacFilters")) {
116 // Next argument is the cluster-wise MAC filters (separated by semicolons).
117 onSignatureMacFilters = parseSignatureMacFilters(args[i+1]);
118 } else if (args[i].equalsIgnoreCase("-offMacFilters")) {
119 // Next argument is the cluster-wise MAC filters (separated by semicolons).
120 offSignatureMacFilters = parseSignatureMacFilters(args[i+1]);
121 } else if (args[i].equalsIgnoreCase("-sout")) {
122 // Next argument is a boolean true/false literal.
123 DUPLICATE_OUTPUT_TO_STD_OUT = Boolean.parseBoolean(args[i+1]);
128 // Prepare file outputter.
129 File outputFile = new File(resultsFile);
130 outputFile.getParentFile().mkdirs();
131 final PrintWriter resultsWriter = new PrintWriter(new FileWriter(outputFile));
132 // Include metadata as comments at the top
133 PrintWriterUtils.println("# Detection results for:", resultsWriter, DUPLICATE_OUTPUT_TO_STD_OUT);
134 PrintWriterUtils.println("# - inputPcapFile: " + pcapFile, resultsWriter, DUPLICATE_OUTPUT_TO_STD_OUT);
135 PrintWriterUtils.println("# - onAnalysisFile: " + onClusterAnalysisFile, resultsWriter, DUPLICATE_OUTPUT_TO_STD_OUT);
136 PrintWriterUtils.println("# - offAnalysisFile: " + offClusterAnalysisFile, resultsWriter, DUPLICATE_OUTPUT_TO_STD_OUT);
137 PrintWriterUtils.println("# - onSignatureFile: " + onSignatureFile, resultsWriter, DUPLICATE_OUTPUT_TO_STD_OUT);
138 PrintWriterUtils.println("# - offSignatureFile: " + offSignatureFile, resultsWriter, DUPLICATE_OUTPUT_TO_STD_OUT);
139 resultsWriter.flush();
141 // Create signature detectors and add observers that output their detected events.
142 List<List<List<PcapPacket>>> onSignature = PrintUtils.deserializeFromFile(onSignatureFile);
143 List<List<List<PcapPacket>>> offSignature = PrintUtils.deserializeFromFile(offSignatureFile);
144 // Load signature analyses
145 List<List<List<PcapPacket>>> onClusterAnalysis = PrintUtils.deserializeFromFile(onClusterAnalysisFile);
146 List<List<List<PcapPacket>>> offClusterAnalysis = PrintUtils.deserializeFromFile(offClusterAnalysisFile);
147 // TODO: FOR NOW WE DECIDE PER SIGNATURE AND THEN WE OR THE BOOLEANS
148 // TODO: SINCE WE ONLY HAVE 2 SIGNATURES FOR NOW (ON AND OFF), THEN IT IS USUALLY EITHER RANGE-BASED OR
149 // TODO: STRICT MATCHING
150 // Check if we should use range-based matching
151 boolean isRangeBasedForOn = PcapPacketUtils.isRangeBasedMatching(onSignature, eps, offSignature);
152 boolean isRangeBasedForOff = PcapPacketUtils.isRangeBasedMatching(offSignature, eps, onSignature);
153 // TODO: WE DON'T DO RANGE-BASED FOR NOW BECAUSE THE RESULTS ARE TERRIBLE FOR LAYER 2 MATCHING
154 // TODO: THIS WOULD ONLY WORK FOR SIGNATURES LONGER THAN 2 PACKETS
155 // boolean isRangeBasedForOn = false;
156 // boolean isRangeBasedForOff = false;
157 // Update the signature with ranges if it is range-based
158 if (isRangeBasedForOn) {
159 onSignature = PcapPacketUtils.useRangeBasedMatching(onSignature, onClusterAnalysis);
161 if (isRangeBasedForOff) {
162 offSignature = PcapPacketUtils.useRangeBasedMatching(offSignature, offClusterAnalysis);
164 Layer2SignatureDetector onDetector = onSignatureMacFilters == null ?
165 new Layer2SignatureDetector(onSignature, TRAINING_ROUTER_WLAN_MAC, ROUTER_WLAN_MAC, signatureDuration,
166 isRangeBasedForOn, eps, onMaxSkippedPackets) :
167 new Layer2SignatureDetector(onSignature, TRAINING_ROUTER_WLAN_MAC, ROUTER_WLAN_MAC,
168 onSignatureMacFilters, signatureDuration, isRangeBasedForOn, eps, onMaxSkippedPackets);
169 Layer2SignatureDetector offDetector = offSignatureMacFilters == null ?
170 new Layer2SignatureDetector(offSignature, TRAINING_ROUTER_WLAN_MAC, ROUTER_WLAN_MAC, signatureDuration,
171 isRangeBasedForOff, eps, offMaxSkippedPackets) :
172 new Layer2SignatureDetector(offSignature, TRAINING_ROUTER_WLAN_MAC, ROUTER_WLAN_MAC, offSignatureMacFilters,
173 signatureDuration, isRangeBasedForOff, eps, offMaxSkippedPackets);
174 final List<UserAction> detectedEvents = new ArrayList<>();
175 onDetector.addObserver((signature, match) -> {
176 UserAction event = new UserAction(UserAction.Type.TOGGLE_ON, match.get(0).get(0).getTimestamp());
177 PrintWriterUtils.println(event, resultsWriter, DUPLICATE_OUTPUT_TO_STD_OUT);
178 detectedEvents.add(event);
180 offDetector.addObserver((signature, match) -> {
181 UserAction event = new UserAction(UserAction.Type.TOGGLE_OFF, match.get(0).get(0).getTimestamp());
182 PrintWriterUtils.println(event, resultsWriter, DUPLICATE_OUTPUT_TO_STD_OUT);
183 detectedEvents.add(event);
186 // Load the PCAP file
189 handle = Pcaps.openOffline(pcapFile, PcapHandle.TimestampPrecision.NANO);
190 } catch (PcapNativeException pne) {
191 handle = Pcaps.openOffline(pcapFile);
193 PcapHandleReader reader = new PcapHandleReader(handle, p -> true, onDetector, offDetector);
195 reader.readFromHandle();
197 String resultOn = "# Number of detected events of type " + UserAction.Type.TOGGLE_ON + ": " +
198 detectedEvents.stream().filter(ua -> ua.getType() == UserAction.Type.TOGGLE_ON).count();
199 String resultOff = "# Number of detected events of type " + UserAction.Type.TOGGLE_OFF + ": " +
200 detectedEvents.stream().filter(ua -> ua.getType() == UserAction.Type.TOGGLE_OFF).count();
201 String onMaximumSkippedPackets = "# Maximum number of skipped packets in ON signature " +
202 Integer.toString(onDetector.getMaxSkippedPackets());
203 String offMaximumSkippedPackets = "# Maximum number of skipped packets in OFF signature " +
204 Integer.toString(offDetector.getMaxSkippedPackets());
205 PrintWriterUtils.println(resultOn, resultsWriter, DUPLICATE_OUTPUT_TO_STD_OUT);
206 PrintWriterUtils.println(resultOff, resultsWriter, DUPLICATE_OUTPUT_TO_STD_OUT);
207 PrintWriterUtils.println(onMaximumSkippedPackets, resultsWriter, DUPLICATE_OUTPUT_TO_STD_OUT);
208 // TODO: We do not use the feature for now because it is essentially the same as signature duration.
209 //for(Integer skippedPackets : onDetector.getSkippedPackets()) {
210 // PrintWriterUtils.println(skippedPackets, resultsWriter, DUPLICATE_OUTPUT_TO_STD_OUT);
212 PrintWriterUtils.println(offMaximumSkippedPackets, resultsWriter, DUPLICATE_OUTPUT_TO_STD_OUT);
213 //for(Integer skippedPackets : offDetector.getSkippedPackets()) {
214 // PrintWriterUtils.println(skippedPackets, resultsWriter, DUPLICATE_OUTPUT_TO_STD_OUT);
216 // Flush output to results file and close it.
217 resultsWriter.flush();
218 resultsWriter.close();
222 * The signature that this {@link Layer2SignatureDetector} is searching for.
224 private final List<List<List<PcapPacket>>> mSignature;
227 * The {@link Layer2ClusterMatcher}s in charge of detecting each individual sequence of packets that together make
228 * up the the signature.
230 private final List<Layer2ClusterMatcher> mClusterMatchers;
233 * For each {@code i} ({@code i >= 0 && i < mPendingMatches.length}), {@code mPendingMatches[i]} holds the matches
234 * found by the {@link Layer2ClusterMatcher} at {@code mClusterMatchers.get(i)} that have yet to be "consumed",
235 * i.e., have yet to be included in a signature detected by this {@link Layer2SignatureDetector} (a signature can
236 * be encompassed of multiple packet sequences occurring shortly after one another on multiple connections).
238 private final List<List<PcapPacket>>[] mPendingMatches;
241 * Maps a {@link Layer2ClusterMatcher} to its corresponding index in {@link #mPendingMatches}.
243 private final Map<Layer2ClusterMatcher, Integer> mClusterMatcherIds;
246 * In charge of reassembling layer 2 packet flows.
248 private final Layer2FlowReassembler mFlowReassembler = new Layer2FlowReassembler();
250 private final List<SignatureDetectorObserver> mObservers = new ArrayList<>();
252 private int mInclusionTimeMillis;
255 * Skipped-packet analysis.
257 private int mMaxSkippedPackets;
258 private List<Integer> mSkippedPackets;
262 public Layer2SignatureDetector(List<List<List<PcapPacket>>> searchedSignature, String trainingRouterWlanMac,
263 String routerWlanMac, int signatureDuration, boolean isRangeBased, double eps,
264 int limitSkippedPackets) {
265 this(searchedSignature, trainingRouterWlanMac, routerWlanMac, null, signatureDuration, isRangeBased,
266 eps, limitSkippedPackets);
269 public Layer2SignatureDetector(List<List<List<PcapPacket>>> searchedSignature, String trainingRouterWlanMac,
270 String routerWlanMac, List<Function<Layer2Flow, Boolean>> flowFilters,
271 int inclusionTimeMillis, boolean isRangeBased, double eps, int limitSkippedPackets) {
272 if (flowFilters != null && flowFilters.size() != searchedSignature.size()) {
273 throw new IllegalArgumentException("If flow filters are used, there must be a flow filter for each cluster " +
274 "of the signature.");
276 mSignature = Collections.unmodifiableList(searchedSignature);
277 List<Layer2ClusterMatcher> clusterMatchers = new ArrayList<>();
278 for (int i = 0; i < mSignature.size(); i++) {
279 List<List<PcapPacket>> cluster = mSignature.get(i);
280 Layer2ClusterMatcher clusterMatcher = flowFilters == null ?
281 new Layer2ClusterMatcher(cluster, trainingRouterWlanMac, routerWlanMac, inclusionTimeMillis,
282 isRangeBased, eps, limitSkippedPackets) :
283 new Layer2ClusterMatcher(cluster, trainingRouterWlanMac, routerWlanMac, flowFilters.get(i),
284 inclusionTimeMillis, isRangeBased, eps, limitSkippedPackets);
285 clusterMatcher.addObserver(this);
286 clusterMatchers.add(clusterMatcher);
288 mClusterMatchers = Collections.unmodifiableList(clusterMatchers);
289 mPendingMatches = new List[mClusterMatchers.size()];
290 for (int i = 0; i < mPendingMatches.length; i++) {
291 mPendingMatches[i] = new ArrayList<>();
293 Map<Layer2ClusterMatcher, Integer> clusterMatcherIds = new HashMap<>();
294 for (int i = 0; i < mClusterMatchers.size(); i++) {
295 clusterMatcherIds.put(mClusterMatchers.get(i), i);
297 mClusterMatcherIds = Collections.unmodifiableMap(clusterMatcherIds);
298 // Register all cluster matchers to receive a notification whenever a new flow is encountered.
299 mClusterMatchers.forEach(cm -> mFlowReassembler.addObserver(cm));
300 mInclusionTimeMillis =
301 inclusionTimeMillis == 0 ? TriggerTrafficExtractor.INCLUSION_WINDOW_MILLIS : inclusionTimeMillis;
302 mMaxSkippedPackets = 0;
303 mSkippedPackets = new ArrayList<>();
306 public int getMaxSkippedPackets() {
307 return mMaxSkippedPackets;
310 public List<Integer> getSkippedPackets() {
311 for (Layer2ClusterMatcher matcher : mClusterMatchers) {
312 mSkippedPackets.addAll(matcher.getSkippedPackets());
314 return mSkippedPackets;
318 public void gotPacket(PcapPacket packet) {
319 // Forward packet processing to the flow reassembler that in turn notifies the cluster matchers as appropriate
320 mFlowReassembler.gotPacket(packet);
324 public void onMatch(AbstractClusterMatcher clusterMatcher, List<PcapPacket> match) {
325 // TODO: a cluster matcher found a match
326 if (clusterMatcher instanceof Layer2ClusterMatcher) {
327 // Add the match at the corresponding index
328 mPendingMatches[mClusterMatcherIds.get(clusterMatcher)].add(match);
329 checkSignatureMatch();
330 // Update maximum number of skipped packets
331 if (mMaxSkippedPackets < ((Layer2ClusterMatcher) clusterMatcher).getMaxSkippedPackets()) {
332 mMaxSkippedPackets = ((Layer2ClusterMatcher) clusterMatcher).getMaxSkippedPackets();
337 public void addObserver(SignatureDetectorObserver observer) {
338 mObservers.add(observer);
341 public boolean removeObserver(SignatureDetectorObserver observer) {
342 return mObservers.remove(observer);
346 @SuppressWarnings("Duplicates")
347 private void checkSignatureMatch() {
348 // << Graph-based approach using Balint's idea. >>
349 // This implementation assumes that the packets in the inner lists (the sequences) are ordered by asc timestamp.
351 // There cannot be a signature match until each Layer3ClusterMatcher has found a match of its respective sequence.
352 if (Arrays.stream(mPendingMatches).noneMatch(l -> l.isEmpty())) {
354 final SimpleDirectedWeightedGraph<Vertex, DefaultWeightedEdge> graph =
355 new SimpleDirectedWeightedGraph<>(DefaultWeightedEdge.class);
356 // Add a vertex for each match found by all cluster matchers.
357 // And maintain an array to keep track of what cluster matcher each vertex corresponds to
358 final List<Vertex>[] vertices = new List[mPendingMatches.length];
359 for (int i = 0; i < mPendingMatches.length; i++) {
360 vertices[i] = new ArrayList<>();
361 for (List<PcapPacket> sequence : mPendingMatches[i]) {
362 Vertex v = new Vertex(sequence);
363 vertices[i].add(v); // retain reference for later when we are to add edges
364 graph.addVertex(v); // add to vertex to graph
367 // Add dummy source and sink vertices to facilitate search.
368 final Vertex source = new Vertex(null);
369 final Vertex sink = new Vertex(null);
370 graph.addVertex(source);
371 graph.addVertex(sink);
372 // The source is connected to all vertices that wrap the sequences detected by cluster matcher at index 0.
373 // Note: zero cost edges as this is just a dummy link to facilitate search from a common start node.
374 for (Vertex v : vertices[0]) {
375 DefaultWeightedEdge edge = graph.addEdge(source, v);
376 graph.setEdgeWeight(edge, 0.0);
378 // Similarly, all vertices that wrap the sequences detected by the last cluster matcher of the signature
379 // are connected to the sink node.
380 for (Vertex v : vertices[vertices.length-1]) {
381 DefaultWeightedEdge edge = graph.addEdge(v, sink);
382 graph.setEdgeWeight(edge, 0.0);
384 // Now link sequences detected by the cluster matcher at index i to sequences detected by the cluster
385 // matcher at index i+1 if they obey the timestamp constraint (i.e., that the latter is later in time than
387 for (int i = 0; i < vertices.length; i++) {
389 if (j < vertices.length) {
390 for (Vertex iv : vertices[i]) {
391 PcapPacket ivLast = iv.sequence.get(iv.sequence.size()-1);
392 for (Vertex jv : vertices[j]) {
393 PcapPacket jvFirst = jv.sequence.get(jv.sequence.size()-1);
394 if (ivLast.getTimestamp().isBefore(jvFirst.getTimestamp())) {
395 DefaultWeightedEdge edge = graph.addEdge(iv, jv);
396 // The weight is the duration of the i'th sequence plus the duration between the i'th
397 // and i+1'th sequence.
398 Duration d = Duration.
399 between(iv.sequence.get(0).getTimestamp(), jvFirst.getTimestamp());
400 // Unfortunately weights are double values, so must convert from long to double.
401 // TODO: need nano second precision? If so, use d.toNanos().
402 // TODO: risk of overflow when converting from long to double..?
403 graph.setEdgeWeight(edge, Long.valueOf(d.toMillis()).doubleValue());
405 // Alternative version if we cannot assume that sequences are ordered by timestamp:
406 // if (iv.sequence.stream().max(Comparator.comparing(PcapPacket::getTimestamp)).get()
407 // .getTimestamp().isBefore(jv.sequence.stream().min(
408 // Comparator.comparing(PcapPacket::getTimestamp)).get().getTimestamp())) {
415 // Graph construction complete, run shortest-path to find a (potential) signature match.
416 DijkstraShortestPath<Vertex, DefaultWeightedEdge> dijkstra = new DijkstraShortestPath<>(graph);
417 GraphPath<Vertex, DefaultWeightedEdge> shortestPath = dijkstra.getPath(source, sink);
418 if (shortestPath != null) {
419 // The total weight is the duration between the first packet of the first sequence and the last packet
420 // of the last sequence, so we simply have to compare the weight against the timeframe that we allow
421 // the signature to span. For now we just use the inclusion window we defined for training purposes.
422 // Note however, that we must convert back from double to long as the weight is stored as a double in
424 if (((long)shortestPath.getWeight()) < mInclusionTimeMillis) {
425 // There's a signature match!
426 // Extract the match from the vertices
427 List<List<PcapPacket>> signatureMatch = new ArrayList<>();
428 for(Vertex v : shortestPath.getVertexList()) {
429 if (v == source || v == sink) {
430 // Skip the dummy source and sink nodes.
433 signatureMatch.add(v.sequence);
434 // As there is a one-to-one correspondence between vertices[] and pendingMatches[], we know that
435 // the sequence we've "consumed" for index i of the matched signature is also at index i in
436 // pendingMatches. We must remove it from pendingMatches so that we don't use it to construct
437 // another signature match in a later call.
438 mPendingMatches[signatureMatch.size()-1].remove(v.sequence);
440 // Declare success: notify observers
441 mObservers.forEach(obs -> obs.onSignatureDetected(mSignature,
442 Collections.unmodifiableList(signatureMatch)));
449 * Encapsulates a {@code List<PcapPacket>} so as to allow the list to be used as a vertex in a graph while avoiding
450 * the expensive {@link AbstractList#equals(Object)} calls when adding vertices to the graph.
451 * Using this wrapper makes the incurred {@code equals(Object)} calls delegate to {@link Object#equals(Object)}
452 * instead of {@link AbstractList#equals(Object)}. The net effect is a faster implementation, but the graph will not
453 * recognize two lists that contain the same items--from a value and not reference point of view--as the same
454 * vertex. However, this is fine for our purposes -- in fact restricting it to reference equality seems more
457 private static class Vertex {
458 private final List<PcapPacket> sequence;
459 private Vertex(List<PcapPacket> wrappedSequence) {
460 sequence = wrappedSequence;