/// <summary>
/// Due to size, data for challenge 4 is hardcoded into the class
/// </summary>
/// <param name="input"></param>
/// <returns></returns>
public string DoChallenge04()
{
SingleCharXORResult bestResult = new SingleCharXORResult();
foreach (string stringToTest in workingSet)
{
//Do what 3 does, but keep our own high score
SingleCharXORDecoder decoder = new SingleCharXORDecoder();
decoder.TestAllKeys(stringToTest);
if (decoder.BestResults.Rating > bestResult.Rating)
{
bestResult = decoder.BestResults;
}
}
return(string.Format("Key: {0}. Input string: {1}. Output string: {2}.", bestResult.BestKey, bestResult.InputString, bestResult.DecodedString.TrimEnd()));
}
/// <summary>
///
/// </summary>
/// <returns></returns>
public string DoChallenge06()
{
//Get the byte array out of the encrypted data
byte[] encryptedData = Convert.FromBase64String(base64EncryptedData);
int lowestKeySize = RepeatingKeyXOR.FindKeySize_CopyFromInternet(encryptedData);
//
//Now the encryption key's length is probably known -- lowestKeySize
//
int numBlocksNeeded = (int)Math.Ceiling((double)encryptedData.Length / (double)lowestKeySize);
//Break up the source into blocks of this size
byte[][] blocks = new byte[numBlocksNeeded][];
for (int i = 0; i < numBlocksNeeded; i++)
{
int blockLen = lowestKeySize;
if (i == numBlocksNeeded - 1)
{
//special case for last block - it may be shorter
blockLen = encryptedData.Length % lowestKeySize;
}
blocks[i] = new byte[blockLen];
Array.Copy(encryptedData, i * lowestKeySize, blocks[i], 0, blockLen);
}
//
//Assuming we guessed the right key size, we now have a series of blocks that should each be decryptable with the full key
//
byte[][] transposed = new byte[lowestKeySize][];
//The first array is numBlocksNeeded arrays of lowestKeySize bytes. e.g. blocks[576][5]
//The transposed array is the reverse -- lowestKeySize arrays of numBlocksNeeded bytes. e.g. blocks[5][576]
int transposedBlockLength = numBlocksNeeded;
//Initialize first
for (int i = 0; i < lowestKeySize; i++)
{
transposed[i] = new byte[transposedBlockLength];
}
for (int block = 0; block < numBlocksNeeded; block++)
{
for (int keyIndex = 0; keyIndex < lowestKeySize; keyIndex++)
{
//Bounds check for our possibly-truncated last block
if (blocks[block].Length > keyIndex)
{
transposed[keyIndex][block] = blocks[block][keyIndex];
}
}
}
//
//We now have a new series of transposed blocks that are each decryptable by a single character
//
StringBuilder sb = new StringBuilder();
foreach (byte[] bytes in transposed)
{
SingleCharXORDecoder decoder = new SingleCharXORDecoder();
decoder.TestAllKeys(bytes);
SingleCharXORResult result = decoder.BestResults;
sb.Append(result.BestKey);
}
string encryptionKey = sb.ToString();
return(encryptionKey);
}
