public static void GenerateStatistics()
{
// INITIALIZE
var statistics = new Statistics()
{
GlobalFrequencies = new Dictionary <char, double>(),
PositionFrequencies = new Dictionary <char, double> [CellPatternSize]
};
for (var i = 0; i < CellPatternSize; i++)
{
statistics.PositionFrequencies[i] = new Dictionary <char, double>();
}
// Load
var maps = LoadMaps();
// Frequencies
var totalDecodedLength = 0;
var totalCoincidence = 0.0;
foreach (var map in maps)
{
totalCoincidence += ComputeCoincidenceRate(map.DecodedData);
totalDecodedLength += map.DecodedData.Length;
for (var i = 0; i < map.DecodedData.Length; i++)
{
var currentLetter = map.DecodedData[i];
if (!statistics.GlobalFrequencies.ContainsKey(currentLetter))
{
statistics.GlobalFrequencies[currentLetter] = 1;
}
else
{
statistics.GlobalFrequencies[currentLetter]++;
}
var patternIndex = i % CellPatternSize;
var positionFrequencies = statistics.PositionFrequencies[patternIndex];
if (!positionFrequencies.ContainsKey(currentLetter))
{
positionFrequencies[currentLetter] = 1;
}
else
{
positionFrequencies[currentLetter]++;
}
}
}
statistics.IndexOfCoincidence = totalCoincidence / maps.Count();
// Normalize
foreach (var k in statistics.GlobalFrequencies.Keys.ToList())
{
statistics.GlobalFrequencies[k] /= totalDecodedLength;
}
for (var i = 0; i < CellPatternSize; i++)
{
var positionFrequencies = statistics.PositionFrequencies[i];
foreach (var k in positionFrequencies.Keys.ToList())
{
positionFrequencies[k] /= totalDecodedLength / CellPatternSize;
}
}
SaveStatistics(statistics);
// Check
//var globalTotalFreq = statistics.GlobalFrequencies.Values.Aggregate(0.0, (acc, freq) => acc + freq);
//var positionTotalFreq = statistics.PositionFrequencies.Sum(p => p.Values.Aggregate(0.0, (acc, freq) => acc + freq));
}
public static void SaveStatistics(Statistics statistics)
{
File.WriteAllText(StatisticsPath, JsonConvert.SerializeObject(statistics, Formatting.Indented));
}
private static double ComputeError(string decrypted, int blockOffset, int blockSize, Statistics statistics)
{
var frequencies = GetFrequencies(decrypted);
return(GetPositionError(decrypted, blockOffset, blockSize, statistics));
}
public static double GetPositionError(string decrypted, int blockOffset, int blockSize, Statistics statistics)
{
var distance = 0.0;
for (var i = 0; i < decrypted.Length; i++)
{
var absolutePosition = blockSize * i + blockOffset;
var positionStatistics = statistics.PositionFrequencies[absolutePosition % CellPatternSize];
var currentData = decrypted[i];
if (positionStatistics.ContainsKey(currentData))
{
distance += (1 - positionStatistics[currentData]);
}
else
{
distance += 10;
}
}
return(distance);
}
private static ComputedKey GuessKey(string message, int keyLength, Statistics statistics)
{
var alternatives = new Dictionary <int, List <(int, double)> >();
var blockSize = keyLength;
var numberOfBlock = (int)Math.Ceiling(message.Length / (double)blockSize);
var offsetOverflow = message.Length % blockSize;
var key = new StringBuilder();
for (var blockOffset = 0; blockOffset < blockSize; blockOffset++)
{
alternatives.Add(blockOffset, new List <(int, double)>());
var bestError = double.MaxValue;
var bestXor = -1;
// Only between thoses
for (var xorKey = MinKeyXor; xorKey <= MaxKeyXor; xorKey++)
{
var numberOfBlockAffected = offsetOverflow > 0 ?
blockOffset > offsetOverflow ? numberOfBlock - 1 : numberOfBlock : numberOfBlock;
var decryptedBlock = new char[numberOfBlockAffected];
for (var blockNumber = 0; blockNumber < numberOfBlock; blockNumber++)
{
var absoluteOffset = blockNumber * blockSize + blockOffset;
if (absoluteOffset < message.Length)
{
var currentData = message[absoluteOffset];
decryptedBlock[blockNumber] = (char)(currentData ^ xorKey);
}
}
var decrypted = HttpUtility.UrlDecode(new string(decryptedBlock));
var error = ComputeError(decrypted, blockOffset, blockSize, statistics);
if (error <= bestError)
{
if (error == bestError)
{
if (bestXor != -1)
{
alternatives[blockOffset].Add((xorKey, error));
}
}
else
{
var clampedValue = error * ErrorClamp;
alternatives[blockOffset].RemoveAll(x => x.Item2 > clampedValue);
alternatives[blockOffset].Add((xorKey, error));
}
bestError = error;
bestXor = xorKey;
}
}
key.Append((char)bestXor);
}
// Shift back the key with its checksum
var computedKey = key.ToString();
int shift = int.Parse(Checksum(computedKey), NumberStyles.HexNumber) * 2;
var finalKey = RightRotateShift(computedKey, shift);
return(new ComputedKey
{
Value = finalKey,
Alternatives = alternatives.Where(x => x.Value.Count > 1).ToDictionary(x => x.Key, x => x.Value)
});
}
