javax.crypto working differently in different versions of Android OS?

Question

I'm using this code snippet to encrypt/decrypt data in my app's database:

http://www.androidsnippets.com/encryptdecrypt-strings

It appears that the javax.crypto.KeyGenerator.generateKey() operation works differently in Android 2.3.3 OS than in other (previous?) versions. Naturally, this presents a major problem for my users when they upgrade their device from 2.2 to 2.3.3 and the app starts throwing errors decrypting the database.

Is this a known issue? Am I using the crypto library incorrectly? Anyone have any suggestions on how to address this so that data encrypted in 2.2 is able to be decrypted in 2.3.3?

I built a test app that feeds values through the encrypt function. When I run it on a 2.2 AVD, I get one result. When I run it on a 2.3.3 AVD, I get a different result.

    import java.security.SecureRandom;

    import javax.crypto.Cipher;
    import javax.crypto.KeyGenerator;
    import javax.crypto.SecretKey;
    import javax.crypto.spec.SecretKeySpec;

    import android.app.Activity;
    import android.os.Bundle;
    import android.widget.TextView;

    public class main extends Activity {
        TextView tvOutput;
        static String out;
        String TEST_STRING = "abcdefghijklmnopqrstuvwxyz";
        String PASSKEY = "ThePasswordIsPassord";

        /** Called when the activity is first created. */
        @Override
        public void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.main);
            tvOutput = (TextView) findViewById(R.id.tvOutput);
        }

        @Override
        public void onResume() {
            super.onResume();
            out = "";
            runTest();
            tvOutput.setText(out);
        }

        private void runTest() {
            out = "Test string: " + TEST_STRING + "\n";
            out += "Passkey: " + PASSKEY + "\n";
            try {
                out += "Encrypted: " + encrypt(PASSKEY, TEST_STRING) + "\n";
            } catch (Exception e) {
                out += "Error: " + e.getMessage() + "\n";
                e.printStackTrace();
            }

        }

        public static String encrypt(String seed, String cleartext)
        throws Exception {
            byte[] rawKey = getRawKey(seed.getBytes());
            byte[] result = encrypt(rawKey, cleartext.getBytes());
            return toHex(result) + "\n" + "Raw Key: " + String.valueOf(rawKey)
                    + "\n";
        }

        private static byte[] getRawKey(byte[] seed) throws Exception {
            KeyGenerator kgen = KeyGenerator.getInstance("AES");
            SecureRandom sr = SecureRandom.getInstance("SHA1PRNG");
            sr.setSeed(seed);
            kgen.init(128, sr); // 192 and 256 bits may not be available
            SecretKey skey = kgen.generateKey();
            byte[] raw = skey.getEncoded();
            return raw;
        }

        private static byte[] encrypt(byte[] raw, byte[] clear) throws Exception {
            SecretKeySpec skeySpec = new SecretKeySpec(raw, "AES");
            Cipher cipher = Cipher.getInstance("AES");
            cipher.init(Cipher.ENCRYPT_MODE, skeySpec);
                byte[] encrypted = cipher.doFinal(clear);
            return encrypted;
        }

        public static String toHex(String txt) {
            return toHex(txt.getBytes());
        }

        public static String fromHex(String hex) {
            return new String(toByte(hex));
        }

        public static byte[] toByte(String hexString) {
            int len = hexString.length() / 2;
            byte[] result = new byte[len];
            for (int i = 0; i < len; i++)
                result[i] = Integer.valueOf(hexString.substring(2 * i, 2 * i + 2),
                        16).byteValue();
            return result;
        }

        public static String toHex(byte[] buf) {
            if (buf == null)
                return "";
            StringBuffer result = new StringBuffer(2 * buf.length);
            for (int i = 0; i < buf.length; i++) {
                appendHex(result, buf[i]);
            }
            return result.toString();
        }

         private final static String HEX = "0123456789ABCDEF";

        private static void appendHex(StringBuffer sb, byte b) {
            sb.append(HEX.charAt((b >> 4) & 0x0f)).append(HEX.charAt(b & 0x0f));
        }
    }

My main.xml layout looks like this:

    <?xml version="1.0" encoding="utf-8"?>
    <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
        android:orientation="vertical" android:layout_width="fill_parent"
        android:layout_height="fill_parent">
        <TextView android:layout_width="fill_parent"
            android:layout_height="wrap_content" android:id="@+id/tvOutput" />
    </LinearLayout>

I can't post links or images since I'm a new users, but you can decipher the URLs for the following two images if you want to see the results:

What I get from 2.2:

..and from 2.3.3:

Answer 1

You are misusing a pseudo random number generator and it's seed as a key derivation function - this is really really bad style. The pseudo random number generator "SHA1PRNG" is not a standard like AES - therefore you never know what implementation you get. See also Is there a SHA1PRNG standard?

It makes me no wonder that you get different results. Getting a deterministic result based on a given seed is not a property you can expect from a pseudo random number functions.

If you want to derive a cryptographic key from a password please use a Key Derivation Function like PKCS #5 / PBKDF2. An implementation of PBKDF2 is AFAIR included in Bouncy Castle.

Answer 2

The answer is in this SO question: BouncyCastle AES error when upgrading to 1.45

Answer 3

I'd like to thank everyone that contributed to this question.

Here is what I ultimately came up with as an example for how to encrypt/decrypt using a password, that seems consistent between Android 2.2 and 2.3.3.

Main Activity:

package cc.ndl.testencryption;

import android.app.Activity;
import android.os.Bundle;
import android.widget.TextView;

public class main extends Activity {
    TextView tvOutput;
    static String out;
    String TEST_STRING = "abcdefghijklmnopqrstuvwxyz";
    static String PASSKEY = "ThePasswordIsPassord";
    static byte[] SALT = { 1, 2, 4, 5 };
    static int ITERATIONS = 1979;

    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        tvOutput = (TextView) findViewById(R.id.tvOutput);
    }

    @Override
    public void onResume() {
        super.onResume();
        out = "";
        runTest();
        tvOutput.setText(out);
    }

    private void runTest() {
        out = "Test string: " + TEST_STRING + "\n";
        out += "Passkey: " + PASSKEY + "\n";
        try {
            Crypto crypto = new Crypto(PASSKEY);
            String encryptedData = crypto.encrypt(TEST_STRING);
            out += "Encrypted: " + encryptedData + "\n";
            out += "Decrypted: " + crypto.decrypt(encryptedData);
        } catch (Exception e) {
            out += "Error: " + e.getMessage() + "\n";
            e.printStackTrace();
        }

    }
}

Main Layout:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical" android:layout_width="fill_parent"
    android:layout_height="fill_parent">
    <TextView android:layout_width="fill_parent"
        android:layout_height="wrap_content" android:id="@+id/tvOutput" />
</LinearLayout>

Crypto Object:

package cc.ndl.testencryption;

import java.security.spec.AlgorithmParameterSpec;
import java.security.spec.KeySpec;

import javax.crypto.Cipher;
import javax.crypto.SecretKey;
import javax.crypto.SecretKeyFactory;
import javax.crypto.spec.PBEKeySpec;
import javax.crypto.spec.PBEParameterSpec;

public class Crypto {

    Cipher ecipher;
    Cipher dcipher;

    // 8-byte Salt
    byte[] salt = { 1, 2, 4, 5, 7, 8, 3, 6 };

    // Iteration count
    int iterationCount = 1979;

    Crypto(String passPhrase) {
        try {
            // Create the key
            KeySpec keySpec = new PBEKeySpec(passPhrase.toCharArray(), salt,
                    iterationCount);
            SecretKey key = SecretKeyFactory.getInstance(
                    "PBEWITHSHA256AND128BITAES-CBC-BC").generateSecret(keySpec);
            ecipher = Cipher.getInstance(key.getAlgorithm());
            dcipher = Cipher.getInstance(key.getAlgorithm());

            // Prepare the parameter to the ciphers
            AlgorithmParameterSpec paramSpec = new PBEParameterSpec(salt,
                    iterationCount);

            // Create the ciphers
            ecipher.init(Cipher.ENCRYPT_MODE, key, paramSpec);
            dcipher.init(Cipher.DECRYPT_MODE, key, paramSpec);
        } catch (Exception e) {
        }
    }

    public String encrypt(String str) {
        String rVal;
        try {
            // Encode the string into bytes using utf-8
            byte[] utf8 = str.getBytes("UTF8");

            // Encrypt
            byte[] enc = ecipher.doFinal(utf8);

            // Encode bytes to base64 to get a string
            rVal = toHex(enc);
        } catch (Exception e) {
            rVal = "Error encrypting: " + e.getMessage();
        }
        return rVal;
    }

    public String decrypt(String str) {
        String rVal;
        try {
            // Decode base64 to get bytes
            byte[] dec = toByte(str);

            // Decrypt
            byte[] utf8 = dcipher.doFinal(dec);

            // Decode using utf-8
            rVal = new String(utf8, "UTF8");
        } catch (Exception e) {
            rVal = "Error encrypting: " + e.getMessage();
        }
        return rVal;
    }

    private static byte[] toByte(String hexString) {
        int len = hexString.length() / 2;
        byte[] result = new byte[len];
        for (int i = 0; i < len; i++)
            result[i] = Integer.valueOf(hexString.substring(2 * i, 2 * i + 2),
                    16).byteValue();
        return result;
    }

    private static String toHex(byte[] buf) {
        if (buf == null)
            return "";
        StringBuffer result = new StringBuffer(2 * buf.length);
        for (int i = 0; i < buf.length; i++) {
            appendHex(result, buf[i]);
        }
        return result.toString();
    }

    private final static String HEX = "0123456789ABCDEF";

    private static void appendHex(StringBuffer sb, byte b) {
        sb.append(HEX.charAt((b >> 4) & 0x0f)).append(HEX.charAt(b & 0x0f));
    }
}