public string Analyse(string plainText, string cipherText)
{
MatrixOP r = new MatrixOP();
//throw new NotImplementedException();
Dictionary <char, int> DT = new Dictionary <char, int>();
Dictionary <int, char> CT = new Dictionary <int, char>();
int cnt = 0;
for (char c = 'a'; c <= 'z'; c++)
{
DT[c] = cnt;
CT[cnt] = c;
cnt++;
}
string[] split = new string[plainText.Length / 2 + (plainText.Length % 2 == 0 ? 0 : 1)];
for (int i = 0; i < split.Length; i++)
{
split[i] = plainText.Substring(i * 2, i * 2 + 2 > plainText.Length ? 1 : 2);
}
string[] splitc = new string[cipherText.Length / 2 + (cipherText.Length % 2 == 0 ? 0 : 1)];
for (int i = 0; i < splitc.Length; i++)
{
splitc[i] = cipherText.ToLower().Substring(i * 2, i * 2 + 2 > cipherText.Length ? 1 : 2);
}
List <string> PermKey = new List <string>();
List <string> ciph = new List <string>();
for (int i = 0; i < split.Length; i++)
{
string perm = "";
string ch = "";
for (int j = i + 1; j < split.Length; j++)
{
perm += split[i] + split[j];
ch += splitc[i] + splitc[j];
PermKey.Add(perm);
ciph.Add(ch);
perm = "";
ch = "";
}
}
List <int> CalInverse = new List <int>();
for (int i = 0; i < PermKey.Count; i++)
{
CalInverse.Add(r.calculateInverse(PermKey[i]));
}
int cnterr = 0;
for (int i = 0; i < CalInverse.Count; i++)
{
if (CalInverse[i] < 0)
{
cnterr++;
}
}
if (cnterr == CalInverse.Count)
{
throw new InvalidAnlysisException();
}
int invMul = 0;
string pl = "";
string ct = "";
for (int i = 0; i < CalInverse.Count; i++)
{
if (CalInverse[i] > 0)
{
invMul = CalInverse[i];
pl = PermKey[i];
ct = ciph[i];
break;
}
}
////////////////////plaintext/////////////////////
int[,] keymat = new int[2, 2];
int idx = 0;
for (int i = 0; i < 2; i++)
{
int cc = idx;
for (int j = 0; j < 2; j++)
{
keymat[i, j] = DT[pl[idx]];
idx++;
cc++;
}
cc = idx;
}
////////////////////ciphertext//////////////////
int[,] cimat = new int[2, 2];
idx = 0;
for (int i = 0; i < 2; i++)
{
int cc = idx;
for (int j = 0; j < 2; j++)
{
cimat[j, i] = DT[ct[idx]];
idx++;
cc++;
}
cc = idx;
}
///////////////////cofactors//////////////////
int A = keymat[0, 0];
int B = keymat[0, 1];
int C = keymat[1, 0];
int D = keymat[1, 1];
keymat[0, 0] = invMul * D;
keymat[1, 1] = invMul * A;
keymat[1, 0] = invMul * (B * -1);
keymat[0, 1] = invMul * (C * -1);
for (int i = 0; i < 2; i++)
{
for (int j = 0; j < 2; j++)
{
while (keymat[i, j] < 0)
{
keymat[i, j] += 26;
}
while (keymat[i, j] > 26)
{
keymat[i, j] -= 26;
}
}
}
int[,] Mulapp = new int[2, 2];
for (int i = 0; i < 2; i++)
{
for (int j = 0; j < 2; j++)
{
int sum = 0;
for (int k = 0; k < 2; k++)
{
sum += cimat[i, k] * keymat[k, j];
}
Mulapp[i, j] = sum % 26;
}
}
string key = "";
for (int i = 0; i < 2; i++)
{
for (int j = 0; j < 2; j++)
{
key += CT[Mulapp[i, j]];
}
}
return(key);
}
