JAVA ANDROID AES CFB NOPADDING

The following example class should give you a good reference of how to encrypt/decrypt properly with all the steps labeled:

public class AES { public static SecretKey generateAESKey(int bits) throws NoSuchAlgorithmException{ //This method is provided as to securely generate a AES key of the given length. //In practice you can specify your own SecureRandom instance. KeyGenerator kgen = KeyGenerator.getInstance("AES"); kgen.init(bits); return kgen.generateKey(); } public static byte[] encrypt(SecretKey key, byte[] plaintext) throws Exception{ //In practice you should specify your SecureRandom implementation. SecureRandom rnd = new SecureRandom(); //Generate random IV of 128-bit (AES block size) byte[] IV = new byte[128 / 8]; rnd.nextBytes(IV); IvParameterSpec IVSpec = new IvParameterSpec(IV); //Create the cipher object to perform AES operations. //Specify Advanced Encryption Standard - Cipher Feedback Mode - No Padding Cipher AESCipher = Cipher.getInstance("AES/CFB/NoPadding"); //Initialize the Cipher with the key and initialization vector. AESCipher.init(Cipher.ENCRYPT_MODE, key, IVSpec); //Encrypts the plaintext data byte[] ciphertext = AESCipher.doFinal(plaintext); /* * The IV must now be transferred with the ciphertext somehow. The easiest * way to accomplish this would be to prepend the IV to the ciphertext * message. */ //Allocate new array to hold ciphertext + IV byte[] output = new byte[ciphertext.length + (128 / 8)]; //Copy the respective parts into the array. System.arraycopy(IV, 0, output, 0, IV.length); System.arraycopy(ciphertext, 0, output, IV.length, ciphertext.length); return output; } public static byte[] decrypt(SecretKey key, byte[] IV, byte[] ciphertext) throws Exception{ //Create the cipher object to perform AES operations. //Specify Advanced Encryption Standard - Cipher Feedback Mode - No Padding Cipher AESCipher = Cipher.getInstance("AES/CFB/NoPadding"); //Create the IvParameterSpec object from the raw IV IvParameterSpec IVSpec = new IvParameterSpec(IV); //Initialize the Cipher with the key and initialization vector. AESCipher.init(Cipher.DECRYPT_MODE, key, IVSpec); //Decrypts the ciphertext data byte[] plaintext = AESCipher.doFinal(ciphertext); return plaintext; } public static void main(String[] args) throws Exception{ //Demo the program String sPlaintext = "rainbows"; //String plaintext byte[] rPlaintext = sPlaintext.getBytes(Charset.forName("UTF-8")); //Raw byte array plaintext //We first need to generate a key of 128-bit SecretKey key = generateAESKey(128); //Encrypt the plaintext byte[] output = encrypt(key, rPlaintext); // ----------------- // //Extract the IV from the encryption output byte[] IV = new byte[128 / 8]; byte[] ciphertext = new byte[output.length - (128 / 8)]; System.arraycopy(output, 0, IV, 0, IV.length); System.arraycopy(output, IV.length, ciphertext, 0, ciphertext.length); //Decrypt the ciphertext byte[] dPlaintext = decrypt(key, IV, ciphertext); String decryptedMessage = new String(dPlaintext, Charset.forName("UTF-8")); //Print stuff out System.out.println("Original message: " + sPlaintext); System.out.println("Original message bytes: " + Arrays.toString(rPlaintext)); System.out.println("Encryption Output bytes: " + Arrays.toString(output)); System.out.println("Decrypted message bytes: " + Arrays.toString(dPlaintext)); System.out.println("Decrypted message: " + decryptedMessage); } } 

Few things to note however:

throws Exception 

is not acceptable. This is only placed for the sake of simplifying code and should never be used in practice. Although some of those checked exceptions like NoSuchAlgorithmException is unlikely to be thrown please be wary that the decrypt() method will thrown exceptions for a failed decryption (i.e. bad key/IV/ciphertext).

Leading onto my next point, you should not rely on the decrypt() method throwing exceptions as a way to validate input. This should be one with a secure one-way hash function such as SHA-2.

Note how the key for encryption/decryption is generated once. AES is a symmetrical block cipher which means that the same key is used for both encryption and decryption. Please keep note of that and not generate a new key between encryption and decryption (you can however generate a new key per encryption if you want, as long as you use the same key to decrypt).