Exemple #1
0
        public string Encrypt(string plainText, string key)
        {
            // construct the arr[5][5] based on PlayFair algorithm.
            construct_array(key);
            char current, next = ' ';
            // this is the String that will contains the encrpted text.
            String ret = "";

            for (int k = 0; k < plainText.Length; k += 2)
            {
                current = plainText[k];
                if (k < plainText.Length - 1)
                {
                    // if there's 2 same adjacent characters seperate them by adding char 'x' in the middle.
                    if (plainText[k + 1] == plainText[k])
                    {
                        next = 'x';
                        k--;
                    }
                    else
                    {
                        next = plainText[k + 1];
                    }
                }
                // if plainText.Length is odd so the last character with paired with char 'x'
                if (k + 1 == plainText.Length)
                {
                    next = 'x';
                    k--;
                }
                // the next 2 character positions in arr[5][5]
                point x1 = find(current);
                point x2 = find(next);

                // here's the 3 conditions of PlayFair algorithm
                if (x1.getJ() == x2.getJ())
                {
                    ret += arr[(x1.getI() + 1) % 5, x1.getJ() % 5];
                    ret += arr[(x2.getI() + 1) % 5, x2.getJ() % 5];
                }
                else if (x1.getI() == x2.getI())
                {
                    ret += arr[(x1.getI()), (x1.getJ() + 1) % 5];
                    ret += arr[x2.getI(), (x2.getJ() + 1) % 5];
                }
                else
                {
                    ret += arr[x1.getI(), x2.getJ()];
                    ret += arr[x2.getI(), x1.getJ()];
                }
            }

            return(ret.ToUpper());
        }
Exemple #2
0
        public string Decrypt(string cipherText, string key)
        {
            construct_array(key);
            char   current, next = ' ';
            String ret = "";

            for (int k = 0; k < cipherText.Length; k += 2)
            {
                current = Char.ToLower(cipherText[k]);
                if (k < cipherText.Length - 1)
                {
                    if (cipherText[k + 1] == cipherText[k])
                    {
                        next = 'x';
                        k--;
                    }
                    else
                    {
                        next = cipherText[k + 1];
                    }
                }
                if (k + 1 == cipherText.Length)
                {
                    next = 'x';
                    k--;
                }
                point x1 = find(Char.ToLower(current));
                point x2 = find(Char.ToLower(next));

                if (x1.getJ() == x2.getJ())
                {
                    if (x1.getI() == 0)
                    {
                        ret += arr[4, x1.getJ()];
                    }
                    else
                    {
                        ret += arr[x1.getI() - 1, x1.getJ()];
                    }

                    if (x2.getI() == 0)
                    {
                        ret += arr[4, x2.getJ()];
                    }
                    else
                    {
                        ret += arr[(x2.getI() - 1), x2.getJ()];
                    }
                }
                else if (x1.getI() == x2.getI())
                {
                    if (x1.getJ() == 0)
                    {
                        ret += arr[x1.getI(), 4];
                    }
                    else
                    {
                        if (arr[(x1.getI()), (x1.getJ() - 1)] != 'x')
                        {
                            ret += arr[(x1.getI()), (x1.getJ() - 1)];
                        }
                    }

                    if (x2.getJ() == 0)
                    {
                        ret += arr[x2.getI(), 4];
                    }
                    else
                    {
                        ret += arr[x2.getI(), (x2.getJ() - 1)];
                    }
                }
                else
                {
                    if (arr[x2.getI(), x1.getJ()] == 'x')
                    {
                        ret += arr[x1.getI(), x2.getJ()];
                        // ret += 'x';
                        continue;
                    }

                    // if (arr[x1.getI(), x2.getJ()] != 'x')
                    ret += arr[x1.getI(), x2.getJ()];
                    if (arr[x2.getI(), x1.getJ()] != 'x')
                    {
                        ret += arr[x2.getI(), x1.getJ()];
                    }
                }
            }

            return(ret.ToUpper());
        }