/// <summary>
/// Finds the most suitable key for the given text
/// The key may not be 100% compatible as there may be some character that is not in the alphabet
/// </summary>
/// <param name="text">String containing all the text from the file</param>
/// <returns>The key value</returns>
private static Int32 FindKey(String text)
{
// splits the text into an array using the whitespace and newline as separator.
var words = text.Split(new char[] { Whitespace, '\r', '\n' })
.Where(word => word != string.Empty).ToArray();
int matchNumber = -1; // this will store the number of words that match from the best key at the time
int matchKey = -1;
//the number of possible keys is the length of the alphabet
for (int i = 0; i <= Alphabet.Length; i++)
{
//this code uses the length of the alphabet as key and tests the number of completely valid english words for the given key
int wordsMatched = 0;
//checks only untill reaches the end of the text or the NumCheckWords variable
for (var j = 0; j < words.Length && j < NumCheckWords; j++)
{
var word = ReplaceWithKey(words[j], i);
if (word.Length > 0 && _spell.TestWord(word))
{
wordsMatched++;
}
}
if (wordsMatched > matchNumber)
{
matchNumber = wordsMatched;
matchKey = i;
}
}
return(matchKey);
}
public static String decode(String cipher)
{
//decodes with the Caesar cipher
List <object> retList = establishVariables();
cipher = cipher.ToLower();
String alphabet = Convert.ToString(retList[0]);
Dictionary <char, int> characterToInteger = retList[1] as Dictionary <char, int>;
Dictionary <int, char> integerToCharacter = retList[2] as Dictionary <int, char>;
char[] cipherText = cipher.ToCharArray(); //so we have a permanent copy
char[] guessText = cipher.ToCharArray(); //this will be manipulated
int iter = 0;
bool found = false; // when to break out of the while loop
while (iter <= 25)
{
// constructs the shift "guess"
var textList = new List <char>();
foreach (char elem in guessText)
{
if (alphabet.Contains(elem.ToString()))
{
int val = characterToInteger[elem];
val = (val + iter) % 26; //performs shift
textList.Add(integerToCharacter[val]);
}
else
{
textList.Add(elem);
}
}
String result = MakeString(textList);
string[] strRes = result.Split(' ');
// checks to see if NetSpell is working correctly
NetSpell.SpellChecker.Dictionary.WordDictionary oDict = new NetSpell.SpellChecker.Dictionary.WordDictionary();
String path = "..//..//en-US.dic";
oDict.DictionaryFile = path;
oDict.Initialize();
NetSpell.SpellChecker.Spelling oSpell = new NetSpell.SpellChecker.Spelling();
oSpell.Dictionary = oDict;
// checks to see if the guess is proper English by at least 50%
double englishThreshold = 0.5;
int sizeOfGuess = strRes.Length;
int properEnglishCount = 0;
foreach (String current in strRes)
{
if (oSpell.TestWord(current))
{
properEnglishCount++;
}
double thresholdCheck = (double)properEnglishCount / (double)sizeOfGuess;
if (thresholdCheck >= englishThreshold)
{
int shiftValue = 26 - iter;
found = true;
}
}
if (found == true)
{
return(result);
}
//iterates the while
iter++;
}
return("I'm sorry, indecipherable with a shift cipher.");
}
public static String decode(String cipherText)
{
List <object> retList = establishVariables();
cipherText = cipherText.ToLower();
String alphabet = Convert.ToString(retList[0]);
Dictionary <char, int> characterToInteger = retList[1] as Dictionary <char, int>;
Dictionary <int, char> integerToCharacter = retList[2] as Dictionary <int, char>;
for (int i = 1; i <= 26; i++)
{
//Iterate through all possible "a" values
int inverse = calculateInverse(i);
if (inverse == 0 || i == 13)
{
// This value of a has no inverse, skip
}
else
{
for (int b = 0; b <= 26; b++)
{
//iterate through all possible "b" values
var cipherTextGuess = new List <char>();
foreach (char letter in cipherText)
{
if (alphabet.Contains(letter.ToString()))
{
int value = characterToInteger[letter];
int affineValue = (inverse * (value - b)) % 26; //perform affine calculation
if (affineValue < 0)
{
affineValue = affineValue + 26;
}
char charValue = integerToCharacter[affineValue];
cipherTextGuess.Add(charValue);
}
else
{
cipherTextGuess.Add(letter);
}
}
String guess = MakeString(cipherTextGuess);
string[] strRes = guess.Split(' ');
NetSpell.SpellChecker.Dictionary.WordDictionary oDict = new NetSpell.SpellChecker.Dictionary.WordDictionary();
String path = "..//..//en-US.dic";
oDict.DictionaryFile = path;
oDict.Initialize();
NetSpell.SpellChecker.Spelling oSpell = new NetSpell.SpellChecker.Spelling();
oSpell.Dictionary = oDict;
// checks to see if the guess is proper English by at least 60%
double englishThreshold = 0.6;
int sizeOfGuess = strRes.Length;
int properEnglishCount = 0;
foreach (String current in strRes)
{
if (oSpell.TestWord(current))
{
properEnglishCount++;
}
double thresholdCheck = (double)properEnglishCount / (double)sizeOfGuess;
if (thresholdCheck >= englishThreshold)
{
//if threshold met, return guess
return(guess);
}
}
}
}
}
return("I'm sorry, indecipherable cipher.");
}
