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RSAtext.java
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RSAtext.java
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import java.util.ArrayList;
import java.util.HashSet;
import java.util.List;
import java.util.Random;
public class RSAtext{
private static HashSet<Integer> prime = new HashSet<>();
private static Integer public_key = null;
private static Integer private_key = null;
private static Integer n = null;
private static Random random = new Random();
public static void main(String[] args)
{
primeFiller();
setKeys();
String message = "Hello World!";
// System.out.println("Enter the message:");
// message = new Scanner(System.in).nextLine();
List<Integer> coded = encoder(message);
System.out.print("Plain Text:");
System.out.println(message);
System.out.print ("Encryption: ");
System.out.println(String.join("", coded.stream().map(Object::toString).toArray(String[] ::new)));
System.out.print("Decrypted Text:");
System.out.print(decoder(coded));
}
public static void primeFiller()
{
boolean[] sieve = new boolean[250];
for (int i = 0; i < 250; i++) {
sieve[i] = true;
}
sieve[0] = false;
sieve[1] = false;
for (int i = 2; i < 250; i++) {
for (int j = i * 2; j < 250; j += i) {
sieve[j] = false;
}
}
for (int i = 0; i < sieve.length; i++) {
if (sieve[i]) {
prime.add(i);
}
}
}
public static int pickRandomPrime()
{
int k = random.nextInt(prime.size());
List<Integer> primeList = new ArrayList<>(prime);
int ret = primeList.get(k);
prime.remove(ret);
return ret;
}
public static void setKeys()
{
int prime1 = pickRandomPrime();
int prime2 = pickRandomPrime();
n = prime1 * prime2;
int fi = (prime1 - 1) * (prime2 - 1);
int e = 2;
while (true) {
if (gcd(e, fi) == 1) {
break;
}
e += 1;
}
public_key = e;
int d = 2;
while (true) {
if ((d * e) % fi == 1) {
break;
}
d += 1;
}
private_key = d;
}
public static int encrypt(int message)
{
int e = public_key;
int encrypted_text = 1;
while (e > 0) {
encrypted_text *= message;
encrypted_text %= n;
e -= 1;
}
return encrypted_text;
}
public static int decrypt(int encrypted_text)
{
int d = private_key;
int decrypted = 1;
while (d > 0) {
decrypted *= encrypted_text;
decrypted %= n;
d -= 1;
}
return decrypted;
}
public static int gcd(int a, int b)
{
if (b == 0) {
return a;
}
return gcd(b, a % b);
}
public static List<Integer> encoder(String message)
{
List<Integer> encoded = new ArrayList<>();
for (char letter : message.toCharArray()) {
encoded.add(encrypt((int)letter));
}
return encoded;
}
public static String decoder(List<Integer> encoded)
{
StringBuilder s = new StringBuilder();
for (int num : encoded) {
s.append((char)decrypt(num));
}
return s.toString();
}
}