/// <summary>
/// Wanted to come up with a value that I could use to tell which frequencylist would be a better solution so,
/// the greater the number returned from this, the better probability that the it's the solution
/// </summary>
///
/// <param name="characterFrequencyList">Frequencies to check</param>
/// <param name="originalText">The text that the FrequecyList is from</param>
///
/// <returns>Amount of "correctness" the FrequencyList has towards the English frequencies</returns>
public double GetDifference(CharacterFrequencyList characterFrequencyList, string originalText)
{
double totalDiff = 0;
int textLen = originalText.Length;
foreach (CharacterFrequency cf in characterFrequencyList.CharacterFrequencies) //For each character frequency in the list
{
double myPercent = (((double)cf.Frequency / (double)textLen)) * 100; //Transform the int (amount of times it appears in the string) to a double (percentage of it's appearance)
double englishFreq = freqs[cf.Character]; //Get the english frquency
//Console.WriteLine("MyPercent = " + myPercent + ", English = " + englishFreq);
//Take myPercent away from the englishFreq (if myPercent is close, the amount taken is less therefore the total is increased more)
double differenceBetween = englishFreq - myPercent;
if (englishFreq < myPercent)
{
differenceBetween = myPercent - englishFreq;
}
totalDiff += differenceBetween;//Incease the total by the difference
}
return(totalDiff);
}
public string BruteForce(string cipherText)
{
StringBuilder buff = new StringBuilder();
CharacterFrequencyList frequencies = fa.AnalyseFrequency(cipherText); //Get the character frequencies
CharacterFrequency probablyE = frequencies.ProbablyE; // Character that is most likly to be E
CharacterFrequency probablyT = frequencies.ProbablyT; // Character that is most likly to be T
int p = alphabet.GetCharacterIndex('E'); //Get the index of E
int q = alphabet.GetCharacterIndex('T'); //Get the index of T
int r = alphabet.GetCharacterIndex(probablyE.Character); //Get the index of the ciphered E
int s = alphabet.GetCharacterIndex(probablyT.Character); //Get the index of the ciphered T
int D = Mod(p - q, 26); //Work out what D is (difference)
int invD = Inverse(D); //Get the multiplicative inverse
/*
* Working out :D
* a x indexOf('E') + b = indexOf ( probablyE ) MOD 26, indexOf(e) = p, indexOf( probablyE ) = r
* a x indexOf('T') + b = indexOf ( probablyT ) MOD 26, indexOf(t) = q, indexOf( probablyT ) = s
*
* D = p - q;
*
* a = D^-1 (r-s) MOD 26
* b = D^-1 (ps - qr) MOD 26
*/
int a = Mod(invD * (r - s), 26); //Work out the first part of the key (a)
int b = Mod(invD * ((p * s) - (q * r)), 26); //Work out the second part of the key (b)
Console.WriteLine("Found key: a={0}, b={1}", a, b);
buff.Append(string.Format("Key: ({0},{1}) ", a, b));
buff.Append(string.Format("\nDeciphered Text:\n{0}", Decipher(cipherText, a, b)));
return(buff.ToString()); //Return the deciphered message
}
}; //I'm not changing anything in the dictionary, might as well readonly
/// <summary>
/// Used to get the character frequencies in a string
/// </summary>
///
/// <param name="cipherText">The text to get the frequency of the characters for</param>
///
/// <returns>CharacterFrequencyList that contains the diferent characters and their frequency in the string</returns>
public CharacterFrequencyList AnalyseFrequency(string cipherText)
{
if (string.IsNullOrEmpty(cipherText)) //If it's null
{
throw new ArgumentException(string.Format("Sorry but, \"{0}\" cannot be analyised because it's null/empty", cipherText)); //Throw an exception so they know something screwed up
}
//Create a new list
CharacterFrequencyList frequencies = new CharacterFrequencyList();
int textLen = cipherText.Length;
for (int i = 0; i < textLen; i++) //Loop through all the characters in the string
{
char c = cipherText[i];
if (c == '\n' || char.IsWhiteSpace(c)) //If it's not a letter
{
continue; //Skip!
}
frequencies.AddTo(c); //Increase it's frequency
}
return(frequencies); //Return the list
}
