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 Challenge5Prep_RoundtripXor()
{
const string plaintext = "We have nothing to fear but fear itself";
var transform = new XorCryptoTransform(Encoding.ASCII.GetBytes("the key!"));
var stream = new MemoryStream();
using (var writerStream = new CryptoStream(stream, transform, CryptoStreamMode.Write))
using (var writer = new StreamWriter(writerStream, Encoding.ASCII, 4096, true))
writer.Write(plaintext);
var cipherStream = new MemoryStream(stream.ToArray());
using (var readerStream = new CryptoStream(cipherStream, transform, CryptoStreamMode.Read))
using (var reader = new StreamReader(readerStream))
Assert.AreEqual(plaintext, reader.ReadToEnd());
}
public void Challenge5Prep_RoundtripXor()
{
const string plaintext = "We have nothing to fear but fear itself";
var transform = new XorCryptoTransform(Encoding.ASCII.GetBytes("the key!"));
var stream = new MemoryStream();
using (var writerStream = new CryptoStream(stream, transform, CryptoStreamMode.Write))
using (var writer = new StreamWriter(writerStream, Encoding.ASCII, 4096, true))
writer.Write(plaintext);
var cipherStream = new MemoryStream(stream.ToArray());
using (var readerStream = new CryptoStream(cipherStream, transform, CryptoStreamMode.Read))
using (var reader = new StreamReader(readerStream))
Assert.AreEqual(plaintext, reader.ReadToEnd());
}
public void Challenge5_RepeatingKeyXor()
{
var key = Encoding.ASCII.GetBytes("ICE");
const string plaintext = "Burning 'em, if you ain't quick and nimble\nI go crazy when I hear a cymbal";
var transform = new XorCryptoTransform(key);
var stream = new MemoryStream();
using (var cryptoStream = new CryptoStream(stream, transform, CryptoStreamMode.Write))
{
using (var writer = new StreamWriter(cryptoStream))
writer.Write(plaintext);
}
var expected =
Utils.HexToByteArray(
"0b3637272a2b2e63622c2e69692a23693a2a3c6324202d623d63343c2a26226324272765272a282b2f20430a652e2c652a3124333a653e2b2027630c692b20283165286326302e27282f");
var actual = stream.ToArray();
Assert.IsTrue(expected.SequenceEqual(actual));
}
public void Challenge5_RepeatingKeyXor()
{
var key = Encoding.ASCII.GetBytes("ICE");
const string plaintext = "Burning 'em, if you ain't quick and nimble\nI go crazy when I hear a cymbal";
var transform = new XorCryptoTransform(key);
var stream = new MemoryStream();
using (var cryptoStream = new CryptoStream(stream, transform, CryptoStreamMode.Write))
{
using (var writer = new StreamWriter(cryptoStream))
writer.Write(plaintext);
}
var expected =
Utils.HexToByteArray(
"0b3637272a2b2e63622c2e69692a23693a2a3c6324202d623d63343c2a26226324272765272a282b2f20430a652e2c652a3124333a653e2b2027630c692b20283165286326302e27282f");
var actual = stream.ToArray();
Assert.IsTrue(expected.SequenceEqual(actual));
}
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);
}
