AES Error: Given final block not properly padded

Question

I need help with this error: Given final block not properly padded. As you can see from the title, I am working with AES.

Here is the code of line where is error:

 byte[] decrypted = cipher.doFinal(bytes);

Here is the full code:

public class AESCrypt {
private final Cipher cipher;
private final SecretKeySpec key;
private String encryptedText, decryptedText;

public AESCrypt(String password) throws Exception {
    // hash password with SHA-256 and crop the output to 128-bit for key
    MessageDigest digest = MessageDigest.getInstance("SHA-256");
    digest.update(password.getBytes("UTF-8"));
    byte[] keyBytes = new byte[16];
    System.arraycopy(digest.digest(), 0, keyBytes, 0, keyBytes.length);

    cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
    key = new SecretKeySpec(keyBytes, "AES");
}

public String encrypt(String plainText) throws Exception {
    byte[] iv = new byte[cipher.getBlockSize()];
    new SecureRandom().nextBytes(iv);
    AlgorithmParameterSpec spec = new IvParameterSpec(iv);
    cipher.init(Cipher.ENCRYPT_MODE, key, spec);
    byte[] encrypted = cipher.doFinal(plainText.getBytes());
    encryptedText = asHex(encrypted);
    return encryptedText;
}

public String decrypt(String cryptedText) throws Exception {
    byte[] iv = new byte[cipher.getBlockSize()];
    AlgorithmParameterSpec spec = new IvParameterSpec(iv);
    cipher.init(Cipher.DECRYPT_MODE, key, spec);
    // decrypt the message
    byte[] bytes = cryptedText.getBytes("UTF-8");
    byte[] decrypted = cipher.doFinal(bytes);
    decryptedText = asHex(decrypted);
    System.out.println("Desifrovani tekst: " + decryptedText + "\n");

    return decryptedText;
}

public static String asHex(byte buf[]) {
    StringBuilder strbuf = new StringBuilder(buf.length * 2);
    int i;
    for (i = 0; i < buf.length; i++) {
        if (((int) buf[i] & 0xff) < 0x10) {
            strbuf.append("0");
        }
        strbuf.append(Long.toString((int) buf[i] & 0xff, 16));
    }
    return strbuf.toString();
}

public static void main(String[] args) throws Exception {

    System.out.print("....AES....\n");

    String message = "MESSAGE";
    String password = "PASSWORD";

    System.out.println("MSG:" + message);

    AESCrypt aes = new AESCrypt(password);
    String encryptedText = aes.encrypt(message).toString();
    System.out.println("SIFROVANA PORUKA: " + encryptedText);
    String decryptedText = aes.decrypt(encryptedText).toString();       
    System.out.print("DESIFROVANA PORUKA: " + decryptedText);
}

}

Answer 1

Per your comment, you are pretty close to getting the crypto working.

You need to move the IV generation code from your encryption/decryption methods to somewhere else, like so

public AlgorithmParameterSpec getIV() {
AlgorithmParameterSpec ivspec;
byte[] iv = new byte[cipher.getBlockSize()];
new SecureRandom().nextBytes(iv);
ivspec = new IvParameterSpec(iv);
}

then pass that ivspec into both the encrypt and decrypt methods (making them look like encrypt(String,AlgorithmParameterSpec)), so that you have the same iv for both encryption and decryption.

Also, don't call printBase64Binary on the decryptedByteArray, instead call new String(decryptedByteArray, "UTF-8")

Answer 2

You have two problems, first you encode the output into a hex string but don't decode back from it in the decode method. Second you generate an random IV but don't use it again to decode.

public byte[] encrypt(String plainText) throws Exception {
   byte[] iv = new byte[cipher.getBlockSize()];    
   AlgorithmParameterSpec spec = new IvParameterSpec(iv);
   cipher.init(Cipher.ENCRYPT_MODE, key, spec);
   return cipher.doFinal(plainText.getBytes());
}

public String decrypt(byte[] cryptedText) throws Exception {
   byte[] iv = new byte[cipher.getBlockSize()];
   AlgorithmParameterSpec spec = new IvParameterSpec(iv);
   cipher.init(Cipher.DECRYPT_MODE, key, spec);
   // decrypt the message
   byte[] decrypted = cipher.doFinal(cryptedText);
   decryptedText = new String(decrypted, "UTF-8");
   return decryptedText;
}



String decryptedText = aes.decrypt(aes.encrypt(message)).toString();