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AffineCipher.java
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89 lines (76 loc) · 2.99 KB
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import java.io.*;
class AffineCipher {
public static void main(String[] args) throws Exception {
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
File input = new File("FILE PATH FOR INPUT");
File output = new File("FILE PATH FOR OUTPUT");
BufferedReader br1 = new BufferedReader(new FileReader(input));
BufferedWriter or = new BufferedWriter(new FileWriter(output));
System.out.println("Select 1 for Encryption and 2 for decryption: ");
int choice = Integer.parseInt(br.readLine());
if (choice == 1) {
String pt = br1.readLine();
System.out.print("Enter the value of a in Encryption formula (must be coprime to 26): ");
int a = Integer.parseInt(br.readLine());
if (!isCoprime(a, 26)) {
System.out.println("!!Enter a value CoPrime to 26!!\nRun Again with proper value of A");
} else {
System.out.print("Enter the value of b in Encryption formula: ");
int b = Integer.parseInt(br.readLine());
or.write("Encrypted Ciphertext is: " + encryptMessage(pt.toCharArray(), a, b));
}
} else {
String pt = br1.readLine();
System.out.print("Enter the value of a in Encryption formula (must be coprime to 26): ");
int a = Integer.parseInt(br.readLine());
if (!isCoprime(a, 26)) {
System.out.println("!!Enter a value CoPrime to 26!!\nRun Again with proper value of A");
} else {
System.out.print("Enter the value of b in Encryption formula: ");
int b = Integer.parseInt(br.readLine());
or.write("Decrypted Plaintext is: " + decryptCipher(pt, a, b));
}
}
or.close();
}
static String encryptMessage(char[] msg, int a, int b) {
String cipher = "";
for (int i = 0; i < msg.length; i++) {
if (msg[i] != ' ') {
cipher = cipher + (char) ((((a * (msg[i] - 'A')) + b) % 26) + 'A');
} else {
cipher += msg[i];
}
}
return cipher;
}
static String decryptCipher(String cipher, int a, int b) {
String msg = "";
int a_inv = 0;
int flag = 0;
for (int i = 0; i < 26; i++) {
flag = (a * i) % 26;
if (flag == 1) {
a_inv = i;
}
}
for (int i = 0; i < cipher.length(); i++) {
if (cipher.charAt(i) != ' ') {
msg = msg + (char) (((a_inv * ((cipher.charAt(i) + 'A' - b)) % 26)) + 'A');
} else {
msg += cipher.charAt(i);
}
}
return msg;
}
static int gcd(int a, int b) {
if (b == 0)
return a;
return gcd(b, a % b);
}
static boolean isCoprime(int a , int b){
if (gcd(a,b) == 1)
return true;
return false;
}
}