public int Decode(int input)
{
IEnumerable <int> roundKeys = KeyScheduler.GetRoundKeys(RoundCount);
input = AddRoundKey(input, roundKeys.Last());
for (int i = roundKeys.Count() - 2; i >= 0; i--)
{
// Permutation Layer Except Last Round
if (i != RoundCount - 1)
{
input = Permutation.InversePermutate(input);
}
// SBox Substitution
byte[] inputBytes = GetBytes(input);
for (int j = 0; j < 4; j++)
{
inputBytes[j] = Substitution.InverseSubstitute(inputBytes[j]);
}
input = GetInt(inputBytes);
// Add Round Key
input = AddRoundKey(input, roundKeys.ElementAt(i));
}
return(input);
}
private Dictionary <int, double> CalculateOutputDifference(Dictionary <int, int> inputs, List <int> partialKeys)
{
Dictionary <int, double> partialKeyMatchProbabilities = new Dictionary <int, double>();
byte[] inputsOfLastSubBoxes = GetBytes(Characteristic.OutputDifference);
double correctPairs = 0;
foreach (KeyValuePair <int, int> inputPair in inputs)
{
int firstOutput = _spn.Encode(inputPair.Key);
int secondOutput = _spn.Encode(inputPair.Value);
int outputDifference = firstOutput ^ secondOutput;
byte[] outputsOfDifference = GetBytes(outputDifference);
bool invalidPair = false;
for (int i = 0; i < _spn.SubstitutionBoxCount; i++)
{
if (!ActiveSubstitutionBoxesInLastRound.Contains(i))
{
if (outputsOfDifference[i] != 0)
{
invalidPair = true;
break;
}
}
}
if (invalidPair)
{
continue;
}
correctPairs++;
foreach (int partialKey in partialKeys)
{
int firstOutputOfLastSubBoxes = (firstOutput ^ partialKey);
int secondOutputOfLastSubBoxes = (secondOutput ^ partialKey);
byte[] firstOutputsOfLastSubBoxes = GetBytes(firstOutputOfLastSubBoxes);
byte[] secondOutputsOfLastSubBoxes = GetBytes(secondOutputOfLastSubBoxes);
bool partialKeyMatched = true;
for (int i = 0; i < _spn.SubstitutionBoxCount; i++)
{
if (ActiveSubstitutionBoxesInLastRound.Contains(i))
{
firstOutputsOfLastSubBoxes[i] = Substitution.InverseSubstitute(firstOutputsOfLastSubBoxes[i]);
secondOutputsOfLastSubBoxes[i] = Substitution.InverseSubstitute(secondOutputsOfLastSubBoxes[i]);
byte difference = (byte)(firstOutputsOfLastSubBoxes[i] ^ secondOutputsOfLastSubBoxes[i]);
if (difference != inputsOfLastSubBoxes[i])
{
partialKeyMatched = false;
break;
}
}
}
if (partialKeyMatched)
{
if (!partialKeyMatchProbabilities.ContainsKey(partialKey))
{
partialKeyMatchProbabilities.Add(partialKey, 0);
}
partialKeyMatchProbabilities[partialKey]++;
}
}
}
partialKeyMatchProbabilities = partialKeyMatchProbabilities.OrderByDescending(p => p.Value).ToDictionary(k => k.Key, v => v.Value / correctPairs);
return(partialKeyMatchProbabilities);
}