Handling of IV and salt in Java encryption and decryption

Question

So I'm trying to decrypt a message in a method but it doesn't work because I need to do cipher.init(Cipher.ENCRYPT_MODE, secret) before I try to add new IvParameterSpec(iv) to cipher.init(Cipher.DECRYPT_MODE, secret, new IvParameterSpec(iv));. Otherwise, it just returns a NullPointerException I'm wondering if it's possible to do this in a method rather than writing it all the time. I can't really think of a solution so that's why I'm here. Encrypt works fine but not Decrypt.

Project Running: JRE 7

Encrypt Code:

public static String encrypt(String str) {
    try {
        SecureRandom random = new SecureRandom();
        byte[] salt = new byte[16];
        random.nextBytes(salt);

        SecretKeyFactory factory = SecretKeyFactory.getInstance("PBKDF2WithHmacSHA1");
        KeySpec spec = new PBEKeySpec(str.toCharArray(), salt, 65536, 256);
        SecretKey tmp = factory.generateSecret(spec);
        SecretKey secret = new SecretKeySpec(tmp.getEncoded(), "AES");

        Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
        cipher.init(Cipher.ENCRYPT_MODE, secret); //<--- Need to do this before writing IvPerameterSpec,
        // But I think that it's not possible if I have it in another method.
        byte[] encryptedText = cipher.doFinal(str.getBytes("UTF-8"));

        return new String(encryptedText);
    } catch (Exception e) {
        e.printStackTrace();
    }
    return null;
}

Decrypt Code:

public static String decrypt(String str) {
    try {
        SecureRandom random = new SecureRandom();
        byte[] salt = new byte[16];
        random.nextBytes(salt);

        SecretKeyFactory factory = SecretKeyFactory.getInstance("PBKDF2WithHmacSHA1");
        KeySpec spec = new PBEKeySpec(str.toCharArray(), salt, 65536, 256);
        SecretKey tmp = factory.generateSecret(spec);
        SecretKey secret = new SecretKeySpec(tmp.getEncoded(), "AES");
        Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");

        AlgorithmParameters params = cipher.getParameters();
        byte[] iv = params.getParameterSpec(IvParameterSpec.class).getIV();
        cipher.init(Cipher.DECRYPT_MODE, secret, new IvParameterSpec(iv));
        //                                                ^^^ Returns NullPointerException

        byte[] ciphertext = cipher.doFinal(str.getBytes("UTF-8"));
        String decryptedText = new String(cipher.doFinal(ciphertext), "UTF-8");

        return new String(decryptedText);
    } catch (Exception e) {
        e.printStackTrace();
    }
    return null;
}

Exception:

java.lang.NullPointerException
        at me.Sansanvi.Encryption.api.ComputerAPI.decrypt(ComputerAPI.java:149)
        at me.Sansanvi.Encryption.EncryptionMain.initializeFiles(EncryptionMain.java:46)
        at me.Sansanvi.Encryption.EncryptionMain.(EncryptionMain.java:36)
        at me.Sansanvi.Encryption.EncryptionMain$1.run(EncryptionMain.java:23)
        at java.awt.event.InvocationEvent.dispatch(Unknown Source)
        at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
        at java.awt.EventQueue.access$200(Unknown Source)
        at java.awt.EventQueue$3.run(Unknown Source)
        at java.awt.EventQueue$3.run(Unknown Source)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
        at java.awt.EventQueue.dispatchEvent(Unknown Source)
        at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
        at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
        at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
        at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
        at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
        at java.awt.EventDispatchThread.run(Unknown Source)

I changed the methods to the following and they work:

private static final String ALGORITHM = "AES";
    public static byte[] encrypt(byte[] str) {
    try {
        SecretKeySpec secretKey = new SecretKeySpec("MZygpewJsCpRrfOr".getBytes(StandardCharsets.UTF_8), ALGORITHM);
        Cipher cipher = Cipher.getInstance(ALGORITHM);
        cipher.init(Cipher.ENCRYPT_MODE, secretKey);

        return cipher.doFinal(str);
    } catch (Exception e) {
        e.printStackTrace();
    }
    return null;
}
public static byte[] decrypt(byte[] str) {
    try {
        SecretKeySpec secretKey = new SecretKeySpec("MZygpewJsCpRrfOr".getBytes(StandardCharsets.UTF_8), ALGORITHM);
        Cipher cipher = Cipher.getInstance(ALGORITHM);
        cipher.init(Cipher.DECRYPT_MODE, secretKey);

        return cipher.doFinal(str);
    } catch (Exception e) {
        e.printStackTrace();
    }
    return null;
}

I don't get any errors/exceptions anymore but I get this in the console when I close my application:

[0x7FFC837C7430] ANOMALY: use of REX.w is meaningless (default operand size is 64)
[0x7FFC837C7430] ANOMALY: use of REX.w is meaningless (default operand size is 64)
[0x7FFC837C7430] ANOMALY: use of REX.w is meaningless (default operand size is 64)
[0x7FFC837C7430] ANOMALY: use of REX.w is meaningless (default operand size is 64)
[0x7FFC837C7430] ANOMALY: use of REX.w is meaningless (default operand size is 64)
[0x7FFC837C7430] ANOMALY: use of REX.w is meaningless (default operand size is 64)
[0x7FFC837C7430] ANOMALY: use of REX.w is meaningless (default operand size is 64)
[0x7FFC837C7430] ANOMALY: use of REX.w is meaningless (default operand size is 64)

Handling of IV and salt in Java encryption and decryption

1 Answers