105 lines
3.1 KiB
Java
105 lines
3.1 KiB
Java
import java.awt.Point;
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import java.util.Scanner;
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public class PlayfairCipher {
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private static char[][] charTable;
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private static Point[] positions;
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public static void main(String[] args) {
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Scanner sc = new Scanner(System.in);
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String key = prompt("Enter an encryption key (min length 6): ", sc, 6);
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String txt = prompt("Enter the message: ", sc, 1);
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String jti = prompt("Replace J with I? y/n: ", sc, 1);
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boolean changeJtoI = jti.equalsIgnoreCase("y");
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createTable(key, changeJtoI);
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String enc = encode(prepareText(txt, changeJtoI));
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System.out.printf("%nEncoded message: %n%s%n", enc);
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System.out.printf("%nDecoded message: %n%s%n", decode(enc));
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}
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private static String prompt(String promptText, Scanner sc, int minLen) {
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String s;
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do {
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System.out.print(promptText);
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s = sc.nextLine().trim();
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} while (s.length() < minLen);
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return s;
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}
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private static String prepareText(String s, boolean changeJtoI) {
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s = s.toUpperCase().replaceAll("[^A-Z]", "");
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return changeJtoI ? s.replace("J", "I") : s.replace("Q", "");
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}
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private static void createTable(String key, boolean changeJtoI) {
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charTable = new char[5][5];
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positions = new Point[26];
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String s = prepareText(key + "ABCDEFGHIJKLMNOPQRSTUVWXYZ", changeJtoI);
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int len = s.length();
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for (int i = 0, k = 0; i < len; i++) {
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char c = s.charAt(i);
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if (positions[c - 'A'] == null) {
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charTable[k / 5][k % 5] = c;
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positions[c - 'A'] = new Point(k % 5, k / 5);
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k++;
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}
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}
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}
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private static String encode(String s) {
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StringBuilder sb = new StringBuilder(s);
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for (int i = 0; i < sb.length(); i += 2) {
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if (i == sb.length() - 1)
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sb.append(sb.length() % 2 == 1 ? 'X' : "");
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else if (sb.charAt(i) == sb.charAt(i + 1))
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sb.insert(i + 1, 'X');
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}
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return codec(sb, 1);
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}
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private static String decode(String s) {
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return codec(new StringBuilder(s), 4);
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}
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private static String codec(StringBuilder text, int direction) {
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int len = text.length();
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for (int i = 0; i < len; i += 2) {
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char a = text.charAt(i);
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char b = text.charAt(i + 1);
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int row1 = positions[a - 'A'].y;
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int row2 = positions[b - 'A'].y;
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int col1 = positions[a - 'A'].x;
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int col2 = positions[b - 'A'].x;
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if (row1 == row2) {
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col1 = (col1 + direction) % 5;
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col2 = (col2 + direction) % 5;
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} else if (col1 == col2) {
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row1 = (row1 + direction) % 5;
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row2 = (row2 + direction) % 5;
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} else {
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int tmp = col1;
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col1 = col2;
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col2 = tmp;
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}
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text.setCharAt(i, charTable[row1][col1]);
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text.setCharAt(i + 1, charTable[row2][col2]);
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}
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return text.toString();
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}
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}
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