public void Challenge3_SingleByteXorCipher()
{
const string cipherHex = "1b37373331363f78151b7f2b783431333d78397828372d363c78373e783a393b3736";
var cipherData = Utils.HexToByteArray(cipherHex);
double error;
var plainText = SingleByteXorCracker.Crack(cipherData, out error);
const string expected = "Cooking MC's like a pound of bacon";
Assert.AreEqual(expected, plainText);
}
public void Challenge6_BreakRepeatingKeyXor()
{
var data = Utils.GetResourceBase64("RepeatingKeyXor.txt");
var keySizes = Enumerable.Range(2, 40);
// this is slightly different than the approach described in the challenge. We
// convolve the data against itself and look for the lowest "energy" step. This
// is likely where the repeating keys overlap and the plaintext pattern emerges.
var convolvedKeySizes = keySizes.ToDictionary(keySize => keySize, keySize =>
{
var padding = Enumerable.Repeat((byte)0, keySize).ToArray();
return(Utils.Hamming(padding.Concat(data), data.Concat(padding)));
}).OrderBy(pair => pair.Value);
var topKeySizes = convolvedKeySizes.Select(pair => pair.Key).Take(1);
// distribute data into bins that align with first key byte, second key byte, etc.
var transposedBlocks =
topKeySizes.Select(
keySize =>
Enumerable.Range(0, keySize)
.Select(keyOffset => data.Where((x, i) => i % keySize == keyOffset).ToArray()));
var keySizeKeyErrors = transposedBlocks.Select(pair => pair.Select(k =>
{
byte key;
double error;
var result = SingleByteXorCracker.Crack(k, out error, out key);
return(new { Result = result, Key = key, Error = error });
}));
var possibleKeys = keySizeKeyErrors.Select(k => k.Select(r => r.Key).ToArray());
var plaintexts = possibleKeys.ToDictionary(key => key, key =>
{
var transform = new XorCryptoTransform(key);
var stream = new MemoryStream(data);
using (var cryptoStream = new CryptoStream(stream, transform, CryptoStreamMode.Read))
{
using (var reader = new StreamReader(cryptoStream))
return(reader.ReadToEnd());
}
});
var actual = plaintexts.First().Value;
var expected = Utils.GetResourceText("Set1PlainText.txt");
Assert.AreEqual(expected, actual);
}
public void Challenge4_DetectSingleCharacterXor()
{
var lines = Utils.GetResourceLines("DetectSingleCharacterXor.txt");
var lineData = lines.Select(Utils.HexToByteArray);
var errors = lineData.Select(line =>
{
double error;
var result = SingleByteXorCracker.Crack(line, out error);
return(new { Result = result, Error = error });
}).OrderBy(line => line.Error);
var best = errors.First();
const string expected = "Now that the party is jumping\n";
Assert.AreEqual(expected, best.Result);
}
