public void Challenge4_Solution()
{
var inputFile = new StreamReader("Assets/inputForChallenge4.txt");
var results = new Dictionary <string, double>();
while (!inputFile.EndOfStream)
{
var encryptedLine = Converter.FromHexStringToByteArray(inputFile.ReadLine().Trim());
var key = SingleByteXorCipher.FindSingleByteKey(encryptedLine);
var decryptedText = SingleByteXorCipher.Decrypt(encryptedLine, key);
var score = SingleByteXorCipher.ScoreAccordingToEnglishLetterFrequency(Encoding.Default.GetBytes(decryptedText));
results.Add(decryptedText, score);
}
var hiddenMessage = results.OrderByDescending(x => x.Value).First();
Assert.AreEqual("Now that the party is jumping\n", hiddenMessage.Key);
Console.WriteLine($"Score:{hiddenMessage.Value}");
}
public void Challenge3_Solution()
{
var inputByteArray = Converter.FromHexStringToByteArray(_hexStringInput);
var key = SingleByteXorCipher.FindSingleByteKey(inputByteArray);
Assert.AreEqual('X', Convert.ToChar(key));
var decryptedText = SingleByteXorCipher.Decrypt(inputByteArray, key);
Assert.AreEqual("Cooking MC's like a pound of bacon", decryptedText);
}
public void SingleByteXorCipher_Test()
{
// assign
string input = "1b37373331363f78151b7f2b783431333d78397828372d363c78373e783a393b3736";
string key = null;
string expected = "Cooking MC's like a pound of bacon";
// execute
string actual = SingleByteXorCipher.Decrypt(input, out key);
// assert, ignore case
Assert.IsNotNull(actual);
Assert.IsNotNull(key);
Assert.AreEqual(expected, actual, true);
System.Diagnostics.Debug.WriteLine("------------------");
System.Diagnostics.Debug.WriteLine(actual);
System.Diagnostics.Debug.WriteLine("------------------");
}
public void Challenge6_Solution()
{
var inputFile = new StreamReader("Assets/inputForChallenge6.txt").ReadToEnd();
var inputByteArray = Convert.FromBase64String(inputFile);
// Find key size
var keySizeEditDistanceList = new Dictionary <byte, double>();
for (byte candidateKeySize = 2; candidateKeySize < 41; candidateKeySize++)
{
var distanceList = new List <int>();
for (int currentIndex = 0; currentIndex < inputByteArray.Length; currentIndex = currentIndex + candidateKeySize)
{
var first = inputByteArray.Skip(currentIndex).Take(candidateKeySize).ToArray();
var second = inputByteArray.Skip(currentIndex + candidateKeySize).Take(candidateKeySize).ToArray();
var distance = HammingDistance.Calculate(first, second);
distanceList.Add(distance);
}
var avgDistance = distanceList.Average();
keySizeEditDistanceList.Add(candidateKeySize, avgDistance / candidateKeySize);
}
var keySize = keySizeEditDistanceList.OrderBy(x => x.Value).First().Key;
Assert.AreEqual(29, keySize);
// Transpose byte array according to the key size
var blockList = new List <byte[]>();
for (int i = 0; i < inputByteArray.Length; i = i + keySize)
{
blockList.Add(inputByteArray.Skip(i).Take(keySize).ToArray());
}
var lastBlock = blockList.Last();
if (lastBlock.Length < keySize)
{
var expandedLast = new byte[keySize];
for (int i = 0; i < lastBlock.Length; i++)
{
expandedLast[i] = lastBlock[i];
}
blockList.RemoveAt(blockList.Count - 1);
blockList.Add(expandedLast);
}
var transposedBlockList = new List <byte[]>();
for (int i = 0; i < keySize; i++)
{
var transposedBlockArray = new byte[blockList.Count];
for (int j = 0; j < blockList.Count; j++)
{
transposedBlockArray[j] = blockList[j][i];
}
transposedBlockList.Add(transposedBlockArray);
}
// Use single byte xor cipher solution for each block to find the repeating key
var keyList = new List <byte>();
foreach (var block in transposedBlockList)
{
var minScore = 0d;
byte selectedByteCode = 32;
for (byte byteCode = 32; byteCode < 127; byteCode++) // <-- Brute force search for the correct character
{
var output = Xor.Apply(block, byteCode);
var score = SingleByteXorCipher.ScoreAccordingToEnglishLetterFrequency(output);
if (score > minScore)
{
minScore = score;
selectedByteCode = byteCode;
}
}
//Console.WriteLine($"minScore: {minScore} selectedByteCode:{Convert.ToChar(selectedByteCode)}");
keyList.Add(selectedByteCode);
}
var keyByteArray = keyList.ToArray();
Assert.AreEqual("Terminator X: Bring the noise", Encoding.Default.GetString(keyByteArray));
// Decrypt text
var decryptedByteArray = new byte[inputByteArray.Length];
for (int i = 0; i < inputByteArray.Length; i++)
{
decryptedByteArray[i] = (byte)(inputByteArray[i] ^ keyByteArray[i % keySize]);
}
var decryptedText = Encoding.UTF8.GetString(decryptedByteArray);
Console.WriteLine(decryptedText);
}
