protected override bool keyIsValid(string key = null)
{
if (key == null)
{
key = this.Key;
}
string[] ab = key.Split(','); //"a,b"，根据逗号分割字符串key，第一个数为乘数，第二个数为加数0
int aInt = int.Parse(ab[0]);
return(NumberTheory.Gcd(aInt, Scheme.LetterSetSize) == 1);
}
public override (string, bool) Decode(string cipher = null, string key = null)
{
if (cipher == null)
{
cipher = Cipher;
}
if (key == null)
{
key = Key;
}
if (!keyIsValid(key))
{
return(null, false);
}
string[] ab = key.Split(','); //"a,b"，根据逗号分割字符串key，第一个数为乘数，第二个数为加数0
int aInt = int.Parse(ab[0]);
int bInt = int.Parse(ab[1]);
string plain = "";
foreach (char c in cipher)
{
int p = c;
if (c >= 'a' && c <= 'z')
{
if (NumberTheory.Gcd(aInt, Scheme.LetterSetSize) == 1) //只有当 a 与 n 互素的时候, a 才是有模逆的
{
int cInt = (int)NumberTheory.Inverse(aInt, Scheme.LetterSetSize);
p = (((c - 'a' - bInt) * cInt) % Scheme.LetterSetSize) + 'a';
}
}
else if (c >= 'A' && c <= 'Z')
{
if (NumberTheory.Gcd(aInt, Scheme.LetterSetSize) == 1) //只有当 a 与 n 互素的时候, a 才是有模逆的
{
int cInt = (int)NumberTheory.Inverse(aInt, Scheme.LetterSetSize);
p = (((c - 'A' - bInt) * cInt) % Scheme.LetterSetSize) + 'A';
}
}
plain += Convert.ToChar(p);
}
this.Key = key;
this.Plain = plain;
this.Cipher = cipher;
return(plain, true);
}
public override string GenerateKey()
{
Random rand = new Random();
int a = rand.Next(Scheme.LetterSetSize);
while (NumberTheory.Gcd(a, Scheme.LetterSetSize) != 1)
{
a = rand.Next(Scheme.LetterSetSize);
}
string aString = Convert.ToString(a);
string bString = rand.Next(Scheme.LetterSetSize).ToString();
string key = aString + "," + bString;
return(key);
}
public override (string, double) Break(string cipher = null)
{
if (cipher == null)
{
cipher = this.Cipher;
}
string plain = cipher;
double maxProb = FrequencyAnalyst.Analyze(cipher);
for (int i = 0; i < LetterSetSize; i++)
{
if (NumberTheory.Gcd(i, LetterSetSize) == 1)
{
for (int j = 0; j < LetterSetSize; j++)
{
string a = i.ToString();
string b = j.ToString();
string ab = a + "," + b;
(string str, bool ok)result = Decode(cipher, ab);
if (result.ok)
{
double prob = FrequencyAnalyst.Analyze(result.str);
if (prob > maxProb)
{
plain = result.str;
maxProb = prob;
}
}
}
}
}
this.Plain = plain;
ProcessLog.Enqueue(plain);
ProcessLog.Enqueue("");
return(plain, Math.Pow(Math.E, maxProb));
//throw new NotImplementedException();
}
