Merge pull request #292 from Piyush13y/patch-1

AES Encryption/Decryption

ciphers/AESEncryption.java

@@ -0,0 +1,83 @@
+import javax.crypto.Cipher;
+import javax.crypto.KeyGenerator;
+import javax.crypto.SecretKey;
+import javax.xml.bind.DatatypeConverter;
+
+/**
+ * This example program shows how AES encryption and decryption can be done in Java.
+ * Please note that secret key and encrypted text is unreadable binary and hence 
+ * in the following program we display it in hexadecimal format of the underlying bytes.
+ */
+public class AESEncryption {
+ 
+    /**
+     * 1. Generate a plain text for encryption
+     * 2. Get a secret key (printed in hexadecimal form). In actual use this must 
+     * by encrypted and kept safe. The same key is required for decryption.
+     * 
+     */
+    public static void main(String[] args) throws Exception {
+        String plainText = "Hello World";
+        SecretKey secKey = getSecretEncryptionKey();
+        byte[] cipherText = encryptText(plainText, secKey);
+        String decryptedText = decryptText(cipherText, secKey);
+        
+        System.out.println("Original Text:" + plainText);
+        System.out.println("AES Key (Hex Form):"+bytesToHex(secKey.getEncoded()));
+        System.out.println("Encrypted Text (Hex Form):"+bytesToHex(cipherText));
+        System.out.println("Descrypted Text:"+decryptedText);
+        
+    }
+    
+    /**
+     * gets the AES encryption key. In your actual programs, this should be safely
+     * stored.
+     * @return
+     * @throws Exception 
+     */
+    public static SecretKey getSecretEncryptionKey() throws Exception{
+        KeyGenerator generator = KeyGenerator.getInstance("AES");
+        generator.init(128); // The AES key size in number of bits
+        SecretKey secKey = generator.generateKey();
+        return secKey;
+    }
+    
+    /**
+     * Encrypts plainText in AES using the secret key
+     * @param plainText
+     * @param secKey
+     * @return
+     * @throws Exception 
+     */
+    public static byte[] encryptText(String plainText,SecretKey secKey) throws Exception{
+		// AES defaults to AES/ECB/PKCS5Padding in Java 7
+        Cipher aesCipher = Cipher.getInstance("AES");
+        aesCipher.init(Cipher.ENCRYPT_MODE, secKey);
+        byte[] byteCipherText = aesCipher.doFinal(plainText.getBytes());
+        return byteCipherText;
+    }
+    
+    /**
+     * Decrypts encrypted byte array using the key used for encryption.
+     * @param byteCipherText
+     * @param secKey
+     * @return
+     * @throws Exception 
+     */
+    public static String decryptText(byte[] byteCipherText, SecretKey secKey) throws Exception {
+		// AES defaults to AES/ECB/PKCS5Padding in Java 7
+        Cipher aesCipher = Cipher.getInstance("AES");
+        aesCipher.init(Cipher.DECRYPT_MODE, secKey);
+        byte[] bytePlainText = aesCipher.doFinal(byteCipherText);
+        return new String(bytePlainText);
+    }
+    
+    /**
+     * Convert a binary byte array into readable hex form
+     * @param hash
+     * @return 
+     */
+    private static String  bytesToHex(byte[] hash) {
+        return DatatypeConverter.printHexBinary(hash);
+    }
+}