ColumnarTranspositionCipher.java

import java.io.*;
class Columnar {
    char arr[][], encrypt[][], decrypt[][], keya[], keytemp[];

    void createMatrixEncrypt(String s, String key, int row, int column) {
        arr = new char[row][column];
        int k = 0;
        keya = key.toCharArray();
        for (int i = 0; i < row; i++) {
            for (int j = 0; j < column; j++) {
                if (k < s.length()) {
                    arr[i][j] = s.charAt(k);
                    k++;
                } else {
                    arr[i][j] = ' ';
                }
            }
        }
    }

    void createkey(String key, int column) {
        keytemp = key.toCharArray();
        for (int i = 0; i < column - 1; i++) {
            for (int j = i + 1; j < column; j++) {
                if (keytemp[i] > keytemp[j]) {
                    char temp = keytemp[i];
                    keytemp[i] = keytemp[j];
                    keytemp[j] = temp;
                }
            }
        }
    }

    void createMatrixDecrypt(String s, String key, int row, int column) {
        arr = new char[row][column];
        int k = 0;
        keya = key.toCharArray();
        for (int i = 0; i < column; i++) {
            for (int j = 0; j < row; j++) {
                if (k < s.length()) {
                    arr[j][i] = s.charAt(k);
                    k++;
                } else {
                    arr[j][i] = ' ';
                }
            }
        }
    }

    void encrypt(int row, int column) {
        encrypt = new char[row][column];
        for (int i = 0; i < column; i++) {
            for (int j = 0; j < column; j++) {
                if (keya[i] == keytemp[j]) {
                    for (int k = 0; k < row; k++) {
                        encrypt[k][j] = arr[k][i];
                    }
                    keytemp[j] = '?';
                    break;
                }
            }
        }
    }

    void decrypt(int row, int column) {
        decrypt = new char[row][column];
        for (int i = 0; i < column; i++) {
            for (int j = 0; j < column; j++) {
                if (keya[j] == keytemp[i]) {
                    for (int k = 0; k < row; k++) {
                        decrypt[k][j] = arr[k][i];
                    }
                    keya[j] = '?';
                    break;
                }
            }
        }
    }

    void resultEncrypt(int row, int column, char arr[][]) {
        System.out.println("Result:");
        for (int i = 0; i < column; i++) {
            for (int j = 0; j < row; j++) {
                System.out.print(arr[j][i]);
            }
        }
    }

    void resultDecrypt(int row, int column, char arr[][]) {
        System.out.println("Result:");
        for (int i = 0; i < row; i++) {
            for (int j = 0; j < column; j++) {
                System.out.print(arr[i][j]);
            }
        }
    }

    public static void main(String args[]) throws IOException {
        int row, column, choice;
        Columnar obj = new Columnar();
        BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
        System.out.println("Menu:\n1) Encryption\n2) Decryption");
        choice = Integer.parseInt(in.readLine());
        System.out.println("Enter the string:");
        String s = in.readLine();
        System.out.println("Enter the key:");
        String key = in.readLine();
        row = s.length() / key.length();
        if (s.length() % key.length() != 0)
            row++;
        column = key.length();
        if (choice == 1) {
            obj.createMatrixEncrypt(s, key, row, column);
            obj.createkey(key, column);
            obj.encrypt(row, column);
            obj.resultEncrypt(row, column, obj.encrypt);
        } else {
            obj.createMatrixDecrypt(s, key, row, column);
            obj.createkey(key, column);
            obj.decrypt(row, column);
            obj.resultDecrypt(row, column, obj.decrypt);
        }

    }
}