/// <summary>
/// Gets the CharacterFrequency for a character
/// </summary>
///
/// <param name="character">The character to get the frequency of</param>
///
/// <returns>The character frequency of the character</returns>
public CharacterFrequency GetFrequency(char character)
{
foreach (CharacterFrequency cf in characterFrequencies) //For each frequency in the list,
{
if (cf.Character == character) //If the characters are the same,
{
return(cf); //return the frequency
}
}
//If we've reached here, then the list doesn't contain the character
CharacterFrequency toRet = new CharacterFrequency(character); //Creates a frequency of 0
characterFrequencies.Add(toRet); //Adds to the list
return(toRet); //Returns the newly created frequency
}
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
}
/// <summary>
/// Adds 1 to the frequency of the character
/// </summary>
///
/// <param name="character">Character to add 1 to the frequency of</param>
public void AddTo(char character)
{
CharacterFrequency cf = GetFrequency(character); //Get the current frequency (0 if it didn't exist)
cf.Frequency++; //Add 1 to it
}
