public AnonymizedLocation Anonymize(OriginalLocation msc)
{
SimulateOtherUsers(msc); //Only for the purpose of this prototype. Remove for video
var n = AddMessage(msc);
var gmMark = _gm.SubGraph(n);
var m = LocalKSearch(msc.K, msc, gmMark).ToList();
if (!m.Any())
{
return(null);
}
_im.Remove(msc);
_hm.Remove(msc);
_gm.RemoveNode(msc);
var bbox = Mbr(m);
//TODO: Remove for video
_im = new MultidimensionalIndex();
_hm = new ExpirationHeap();
_gm = new ConstraintGraph();
return(new AnonymizedLocation
{
Id = msc.Id,
LatMin = bbox.MinX,
LatMax = bbox.MaxX,
LonMin = bbox.MinY,
LonMax = bbox.MaxY
});
}
private static IEnumerable <OriginalLocation> LocalKSearch(int k, OriginalLocation msc, ConstraintGraph gmMark)
{
var u = gmMark.Nbr(msc).Where(ms => ms.K <= k).ToList();
if (u.Count() < k - 1)
{
return(new List <OriginalLocation>());
}
var l = 0;
while (l != u.Count())
{
l = u.Count();
foreach (var ms in new List <OriginalLocation>(u))
{
if (gmMark.Nbr(ms).Count() < k - 2)
{
u.Remove(ms);
gmMark.RemoveNode(ms);
}
}
}
return(gmMark.FindClique(msc, k));
}
private static BoundingBox Bcn(OriginalLocation m)
{
return(new BoundingBox
{
MinX = m.Lat - m.Dx,
MaxX = m.Lat + m.Dx,
MinY = m.Lon - m.Dy,
MaxY = m.Lon + m.Dy
});
}
public void RemoveNode(OriginalLocation message)
{
//Remove all edges going into the node
foreach (var node in _nodes)
{
node.Edges = node.Edges.Where(edge => edge.To != message).ToList();
}
//Remove the node itself
_nodes.Remove(_nodes.Find(node => node.Message == message));
}
//On a real anonymization server, this method would obviously not exist
private void SimulateOtherUsers(OriginalLocation msc)
{
var rng = new Random();
for (var i = 0; i < rng.Next(10, 21); i++)
{
var location = new OriginalLocation
{
Lat = msc.Lat + (rng.NextDouble() - 0.5) * msc.Dx * 2,
Lon = msc.Lon + (rng.NextDouble() - 0.5) * msc.Dy * 2,
K = msc.K - 1,
Dx = msc.Dx * 1.2,
Dy = msc.Dy * 1.2,
Timestamp = 1000,
Id = $"{i}"
};
AddMessage(location);
}
}
//Credit to myself for this one :P
public IEnumerable <OriginalLocation> FindClique(OriginalLocation msc, int k)
{
var mscNode = _nodes.Find(node => node.Message == msc);
var clique = new List <OriginalLocation>();
foreach (var mscNeighbor in mscNode.Edges.Select(mscEdge => mscEdge.To))
{
clique.Clear();
clique.Add(msc);
clique.Add(mscNeighbor);
ConsiderNeighborsTo(mscNeighbor, clique);
if (clique.Count >= k)
{
return(clique);
}
}
return(new List <OriginalLocation>());
}
private void ConsiderNeighborsTo(OriginalLocation ms, List <OriginalLocation> clique)
{
var msNode = _nodes.Find(node => node.Message == ms);
foreach (var msNeighbor in msNode.Edges.Select(mscEdge => mscEdge.To))
{
if (clique.Contains(msNeighbor))
{
continue;
}
var msNeighborNode = _nodes.Find(node => node.Message == msNeighbor);
if (clique.Any(c => !msNeighborNode.Edges.Select(e => e.To).Contains(c)))
{
continue;
}
clique.Add(msNeighbor);
ConsiderNeighborsTo(msNeighbor, clique);
}
}
public IEnumerable <OriginalLocation> AddMessage(OriginalLocation msc)
{
_im.Add(msc);
_hm.Add(msc);
_gm.AddNode(msc);
var n = _im.RangeSearch(Bcn(msc)).ToList();
foreach (var ms in n.Where(ms => ms != msc))
{
if (Bcn(ms).Contains(new Point {
X = msc.Lat, Y = msc.Lon
}))
{
//Add two edges to simulate a unidirectional graph
_gm.AddEdge(msc, ms);
_gm.AddEdge(ms, msc);
}
}
return(n);
}
public void Add(OriginalLocation location)
{
_messages.Add(location);
}
public void Remove(OriginalLocation location)
{
_messages.Remove(location);
}
public void AddNode(OriginalLocation message)
{
_nodes.Add(new Node(message));
}
public IEnumerable <OriginalLocation> Nbr(OriginalLocation ms)
{
return(_nodes.Find(m => m.Message == ms).Edges.Select(edge => edge.To).ToList());
}
public void AddEdge(OriginalLocation from, OriginalLocation to)
{
var node = _nodes.Find(n => n.Message.Equals(from));
node.Edges.Add(new Edge(from, to));
}
public Edge(OriginalLocation from, OriginalLocation to)
{
From = from;
To = to;
}
public Node(OriginalLocation message)
{
Message = message;
Edges = new List <Edge>();
}