public Analysis(int timeout = 10)
{
sb = new SubstitutionCipher();
NgramsDictionary = parseNgramsFile();
worstScore = Math.Log10(0.01 / totalNgrams);
if (timeout > 30)
{
this.timeout = 10;
}
else
{
this.timeout = timeout;
}
}
public string breakSubstitutionCipher(string cipherText)
{
//current
int count = 0;
string maxKey = SubstitutionCipher.getAlphabet();
double maxScore = -99e9;
string parentKey = maxKey;
double parentScore = maxScore;
DateTime start = DateTime.Now;
while (DateTime.Now.Subtract(start).Seconds <= timeout)
{
count++;
parentKey = sb.generateNewKey();
parentScore = getTextNgramFitness(sb.decode(cipherText, parentKey));
for (int i = 0; i < 1000; i++)//i => iterations since last improvement. If > 1000, we are at local maximum
{
string childKey = sb.swapTwoChars(parentKey);
double childScore = getTextNgramFitness(sb.decode(cipherText, childKey));
if (childScore > parentScore)
{
parentScore = childScore;
parentKey = childKey;
i = 0;//made an improvement, reset counter
}
}
if (parentScore > maxScore)
{
maxScore = parentScore;
maxKey = parentKey;
}
}
return(maxKey);
}
