Merge pull request codec-akash#38 from canigethellomoto/affine

codec-akash · web-flow · commit 8836993c3ab1 · 2020-10-01T19:00:50.000+05:30
Added AffineCipher.java
diff --git a/AffineCipher.java b/AffineCipher.java
@@ -0,0 +1,89 @@
+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;
+    }
+}
