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Hill_Cipher.java#94

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Sirajmolla merged 1 commit intocoder2hacker:mainfromharshitgupta2000:main
Oct 2, 2022
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192 changes: 192 additions & 0 deletionsjava program/Hill_cipher.java
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import java.util.ArrayList;
import java.util.Scanner;
public class HillCipherExample {
//method to accept key matrix
private static int[][] getKeyMatrix() {
Scanner sc = new Scanner(System.in);
System.out.println("Enter key matrix:");
String key = sc.nextLine();
//int len = key.length();
double sq = Math.sqrt(key.length());
if (sq != (long) sq) {
System.out.println("Cannot Form a square matrix");
}
int len = (int) sq;
int[][] keyMatrix = new int[len][len];
int k = 0;
for (int i = 0; i < len; i++)
{
for (int j = 0; j < len; j++)
{
keyMatrix[i][j] = ((int) key.charAt(k)) - 97;
k++;
}
}
return keyMatrix;
}
// Below method checks whether the key matrix is valid (det=0)
private static void isValidMatrix(int[][] keyMatrix) {
int det = keyMatrix[0][0] * keyMatrix[1][1] - keyMatrix[0][1] * keyMatrix[1][0];
// If det=0, throw exception and terminate
if(det == 0) {
throw new java.lang.Error("Det equals to zero, invalid key matrix!");
}
}
// This method checks if the reverse key matrix is valid (matrix mod26 = (1,0,0,1)
private static void isValidReverseMatrix(int[][] keyMatrix, int[][] reverseMatrix) {
int[][] product = new int[2][2];
// Find the product matrix of key matrix times reverse key matrix
product[0][0] = (keyMatrix[0][0]*reverseMatrix[0][0] + keyMatrix[0][1] * reverseMatrix[1][0]) % 26;
product[0][1] = (keyMatrix[0][0]*reverseMatrix[0][1] + keyMatrix[0][1] * reverseMatrix[1][1]) % 26;
product[1][0] = (keyMatrix[1][0]*reverseMatrix[0][0] + keyMatrix[1][1] * reverseMatrix[1][0]) % 26;
product[1][1] = (keyMatrix[1][0]*reverseMatrix[0][1] + keyMatrix[1][1] * reverseMatrix[1][1]) % 26;
// Check if a=1 and b=0 and c=0 and d=1
// If not, throw exception and terminate
if(product[0][0] != 1 || product[0][1] != 0 || product[1][0] != 0 || product[1][1] != 1) {
throw new java.lang.Error("Invalid reverse matrix found!");
}
}
// This method calculates the reverse key matrix
private static int[][] reverseMatrix(int[][] keyMatrix) {
int detmod26 = (keyMatrix[0][0] * keyMatrix[1][1] - keyMatrix[0][1] * keyMatrix[1][0]) % 26; // Calc det
int factor;
int[][] reverseMatrix = new int[2][2];
// Find the factor for which is true that
// factor*det = 1 mod 26
for(factor=1; factor < 26; factor++)
{
if((detmod26 * factor) % 26 == 1)
{
break;
}
}
// Calculate the reverse key matrix elements using the factor found
reverseMatrix[0][0] = keyMatrix[1][1] * factor % 26;
reverseMatrix[0][1] = (26 - keyMatrix[0][1]) * factor % 26;
reverseMatrix[1][0] = (26 - keyMatrix[1][0]) * factor % 26;
reverseMatrix[1][1] = keyMatrix[0][0] * factor % 26;
return reverseMatrix;
}
// This method echoes the result of encrypt/decrypt
private static void echoResult(String label, int adder, ArrayList<Integer> phrase) {
int i;
System.out.print(label);
// Loop for each pair
for(i=0; i < phrase.size(); i += 2) {
System.out.print(Character.toChars(phrase.get(i) + (64 + adder)));
System.out.print(Character.toChars(phrase.get(i+1) + (64 + adder)));
if(i+2 <phrase.size()) {
System.out.print("-");
}
}
System.out.println();
}
// This method makes the actual encryption
public static void encrypt(String phrase, boolean alphaZero)
{
int i;
int adder = alphaZero ? 1 : 0; // For calclulations depending on the alphabet
int[][] keyMatrix;
ArrayList<Integer> phraseToNum = new ArrayList<>();
ArrayList<Integer> phraseEncoded = new ArrayList<>();
// Delete all non-english characters, and convert phrase to upper case
phrase = phrase.replaceAll("[^a-zA-Z]","").toUpperCase();

// If phrase length is not an even number, add "Q" to make it even
if(phrase.length() % 2 == 1) {
phrase += "Q";
}
// Get the 2x2 key matrix from sc
keyMatrix = getKeyMatrix();
// Check if the matrix is valid (det != 0)
isValidMatrix(keyMatrix);
// Convert characters to numbers according to their
// place in ASCII table minus 64 positions (A=65 in ASCII table)
// If we use A=0 alphabet, subtract one more (adder)
for(i=0; i < phrase.length(); i++) {
phraseToNum.add(phrase.charAt(i) - (64 + adder));
}
// Find the product per pair of the phrase with the key matrix modulo 26
// If we use A=1 alphabet and result is 0, replace it with 26 (Z)
for(i=0; i < phraseToNum.size(); i += 2) {
int x = (keyMatrix[0][0] * phraseToNum.get(i) + keyMatrix[0][1] * phraseToNum.get(i+1)) % 26;
int y = (keyMatrix[1][0] * phraseToNum.get(i) + keyMatrix[1][1] * phraseToNum.get(i+1)) % 26;
phraseEncoded.add(alphaZero ? x : (x == 0 ? 26 : x ));
phraseEncoded.add(alphaZero ? y : (y == 0 ? 26 : y ));
}
// Print the result
echoResult("Encoded phrase: ", adder, phraseEncoded);
}
// This method makes the actual decryption
public static void decrypt(String phrase, boolean alphaZero)
{
int i, adder = alphaZero ? 1 : 0;
int[][] keyMatrix, revKeyMatrix;
ArrayList<Integer> phraseToNum = new ArrayList<>();
ArrayList<Integer> phraseDecoded = new ArrayList<>();
// Delete all non-english characters, and convert phrase to upper case
phrase = phrase.replaceAll("[^a-zA-Z]","").toUpperCase();

// Get the 2x2 key matrix from sc
keyMatrix = getKeyMatrix();
// Check if the matrix is valid (det != 0)
isValidMatrix(keyMatrix);
// Convert numbers to characters according to their
// place in ASCII table minus 64 positions (A=65 in ASCII table)
// If we use A=0 alphabet, subtract one more (adder)
for(i=0; i < phrase.length(); i++) {
phraseToNum.add(phrase.charAt(i) - (64 + adder));
}
// Find the reverse key matrix
revKeyMatrix = reverseMatrix(keyMatrix);
// Check if the reverse key matrix is valid (product = 1,0,0,1)
isValidReverseMatrix(keyMatrix, revKeyMatrix);
// Find the product per pair of the phrase with the reverse key matrix modulo 26
for(i=0; i < phraseToNum.size(); i += 2) {
phraseDecoded.add((revKeyMatrix[0][0] * phraseToNum.get(i) + revKeyMatrix[0][1] * phraseToNum.get(i+1)) % 26);
phraseDecoded.add((revKeyMatrix[1][0] * phraseToNum.get(i) + revKeyMatrix[1][1] * phraseToNum.get(i+1)) % 26);
}
// Print the result
echoResult("Decoded phrase: ", adder, phraseDecoded);
}
//main method
public static void main(String[] args) {
String opt, phrase;
byte[] p;
Scanner sc = new Scanner(System.in);
System.out.println("Hill Cipher Implementation (2x2)");
System.out.println("-------------------------");
System.out.println("1. Encrypt text (A=0,B=1,...Z=25)");
System.out.println("2. Decrypt text (A=0,B=1,...Z=25)");
System.out.println("3. Encrypt text (A=1,B=2,...Z=26)");
System.out.println("4. Decrypt text (A=1,B=2,...Z=26)");
System.out.println();
System.out.println("Type any other character to exit");
System.out.println();
System.out.print("Select your choice: ");
opt = sc.nextLine();
switch (opt)
{
case "1":
System.out.print("Enter phrase to encrypt: ");
phrase = sc.nextLine();
encrypt(phrase, true);
break;
case "2":
System.out.print("Enter phrase to decrypt: ");
phrase = sc.nextLine();
decrypt(phrase, true);
break;
case "3":
System.out.print("Enter phrase to encrypt: ");
phrase = sc.nextLine();
encrypt(phrase, false);
break;
case "4":
System.out.print("Enter phrase to decrypt: ");
phrase = sc.nextLine();
decrypt(phrase, false);
break;
}
}
}
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