First of all, I've already seen Android 4.2 broke my AES encrypt/decrypt code and Encryption error on Android 4.2 and the provided solution:

SecureRandom sr = null;
if (android.os.Build.VERSION.SDK_INT >= JELLY_BEAN_4_2) {
    sr = SecureRandom.getInstance("SHA1PRNG", "Crypto");
} else {
    sr = SecureRandom.getInstance("SHA1PRNG");
}

doesn't work for me, because, when decoding data encrypted in Android<4.2 in Android 4.2, I get:

javax.crypto.BadPaddingException: pad block corrupted
at com.android.org.bouncycastle.jcajce.provider.symmetric.util.BaseBlockCipher.engineDoFinal(BaseBlockCipher.java:709)

My code is quite simple, and was working until Android 4.2:

public static byte[] encrypt(byte[] data, String seed) throws Exception {

    KeyGenerator keygen = KeyGenerator.getInstance("AES");
    SecureRandom secrand = SecureRandom.getInstance("SHA1PRNG");
    secrand.setSeed(seed.getBytes());
    keygen.init(128, secrand);

    SecretKey seckey = keygen.generateKey();
    byte[] rawKey = seckey.getEncoded();

    SecretKeySpec skeySpec = new SecretKeySpec(rawKey, "AES");
    Cipher cipher = Cipher.getInstance("AES");
    cipher.init(Cipher.ENCRYPT_MODE, skeySpec);
    return cipher.doFinal(data);
}

public static byte[] decrypt(byte[] data, String seed) throws Exception {

    KeyGenerator keygen = KeyGenerator.getInstance("AES");
    SecureRandom secrand = SecureRandom.getInstance("SHA1PRNG");
    secrand.setSeed(seed.getBytes());
    keygen.init(128, secrand);

    SecretKey seckey = keygen.generateKey();
    byte[] rawKey = seckey.getEncoded();

    SecretKeySpec skeySpec = new SecretKeySpec(rawKey, "AES");
    Cipher cipher = Cipher.getInstance("AES");
    cipher.init(Cipher.DECRYPT_MODE, skeySpec);
    return cipher.doFinal(data);
}

My guess is that the default provider wasn't the only thing that changed in Android 4.2, otherwise my code would work with the proposed solution.

My code was based on some post I found here at StackOverflow a long time ago; I see that it differs from the mentioned posts as it just crypts and decrypts byte arrays, whereas the others solutions crypt and decrypt Strings (HEX Strings, I think).

Does it have to do with the seed? Does it have a min/max length, restriction of chars, etc?

Any idea / solution?

EDIT: After a lot of tests, I see that there are 2 problems:

  1. The provider changed in Android 4.2 (API 17) -> This one is easy to fix, just apply the solution I mentioned at top of the post

  2. BouncyCastle changed from 1.34 to 1.45 in Android 2.2 (API 8)->Android2.3 (API 9), so the decryption problem I previously told is the same as described here: BouncyCastle AES error when upgrading to 1.45

So now the question is: is there any way to recover data crypted in BouncyCastle 1.34 in BouncyCastle 1.45+?

Solution 1

First a disclaimer:

DO NOT ever use SecureRandom to derive a key! This is broken and doesn't make sense!

The following block of code from the question tries to deterministically derive a key from a password, called the "seed" as the password is used to "seed" the random number generator.

KeyGenerator keygen = KeyGenerator.getInstance("AES");
SecureRandom secrand = SecureRandom.getInstance("SHA1PRNG");
secrand.setSeed(seed.getBytes());
keygen.init(128, secrand);
SecretKey seckey = keygen.generateKey();

However, the "SHA1PRNG" algorithm is not well defined and implementations of "SHA1PRNG" may return different or even fully random keys as a result.


If you're reading an AES key from disk, just store the actual key and don't go through this weird dance. You can get a SecretKey for AES usage from the bytes by doing:

    SecretKey key = new SecretKeySpec(keyBytes, "AES");

If you're using a password to derive a key, follow Nelenkov's excellent tutorial with the caveat that a good rule of thumb is the salt size should be the same size as the key output.

The iterationCount (work factor) is of course subject to change and should be changed as CPU power progresses - generally it is recommended not to go lower than 40 to 100K as of 2018. Beware that PBKDF2 only adds a constant time delay to guessing passwords; it is not a replacement for really weak passwords.

It looks like this:

    /* User types in their password: */
    String password = "password";

    /* Store these things on disk used to derive key later: */
    int iterationCount = 1000;
    int saltLength = 32; // bytes; should be the same size as the output (256 / 8 = 32)
    int keyLength = 256; // 256-bits for AES-256, 128-bits for AES-128, etc
    byte[] salt; // Should be of saltLength

    /* When first creating the key, obtain a salt with this: */
    SecureRandom random = new SecureRandom();
    byte[] salt = new byte[saltLength];
    random.nextBytes(salt);

    /* Use this to derive the key from the password: */
    KeySpec keySpec = new PBEKeySpec(password.toCharArray(), salt,
                iterationCount, keyLength);
    SecretKeyFactory keyFactory = SecretKeyFactory
                .getInstance("PBKDF2WithHmacSHA1");
    byte[] keyBytes = keyFactory.generateSecret(keySpec).getEncoded();
    SecretKey key = new SecretKeySpec(keyBytes, "AES");

That's it. Anything else you should not use.

Solution 2

private static final int ITERATION_COUNT = 1000;
private static final int KEY_LENGTH = 256;
private static final String PBKDF2_DERIVATION_ALGORITHM = "PBKDF2WithHmacSHA1";
private static final String CIPHER_ALGORITHM = "AES/CBC/PKCS5Padding";
private static final int PKCS5_SALT_LENGTH = 32;
private static final String DELIMITER = "]";
private static final SecureRandom random = new SecureRandom();

public static String encrypt(String plaintext, String password) {
    byte[] salt  = generateSalt();
    SecretKey key = deriveKey(password, salt);

    try {
        Cipher cipher = Cipher.getInstance(CIPHER_ALGORITHM);
        byte[] iv = generateIv(cipher.getBlockSize());
        IvParameterSpec ivParams = new IvParameterSpec(iv);
        cipher.init(Cipher.ENCRYPT_MODE, key, ivParams);
        byte[] cipherText = cipher.doFinal(plaintext.getBytes("UTF-8"));

        if(salt != null) {
            return String.format("%s%s%s%s%s",
                    toBase64(salt),
                    DELIMITER,
                    toBase64(iv),
                    DELIMITER,
                    toBase64(cipherText));
        }

        return String.format("%s%s%s",
                toBase64(iv),
                DELIMITER,
                toBase64(cipherText));
    } catch (GeneralSecurityException e) {
        throw new RuntimeException(e);
    } catch (UnsupportedEncodingException e) {
        throw new RuntimeException(e);
    }
}

public static String decrypt(String ciphertext, String password) {
    String[] fields = ciphertext.split(DELIMITER);
    if(fields.length != 3) {
        throw new IllegalArgumentException("Invalid encypted text format");
    }
    byte[] salt        = fromBase64(fields[0]);
    byte[] iv          = fromBase64(fields[1]);
    byte[] cipherBytes = fromBase64(fields[2]);
    SecretKey key = deriveKey(password, salt);

    try {
        Cipher cipher = Cipher.getInstance(CIPHER_ALGORITHM);
        IvParameterSpec ivParams = new IvParameterSpec(iv);
        cipher.init(Cipher.DECRYPT_MODE, key, ivParams);
        byte[] plaintext = cipher.doFinal(cipherBytes);
        return new String(plaintext, "UTF-8");
    } catch (GeneralSecurityException e) {
        throw new RuntimeException(e);
    } catch (UnsupportedEncodingException e) {
        throw new RuntimeException(e);
    }
}

private static byte[] generateSalt() {
    byte[] b = new byte[PKCS5_SALT_LENGTH];
    random.nextBytes(b);
    return b;
}

private static byte[] generateIv(int length) {
    byte[] b = new byte[length];
    random.nextBytes(b);
    return b;
}

private static SecretKey deriveKey(String password, byte[] salt) {
    try {
        KeySpec keySpec = new PBEKeySpec(password.toCharArray(), salt, ITERATION_COUNT, KEY_LENGTH);
        SecretKeyFactory keyFactory = SecretKeyFactory.getInstance(PBKDF2_DERIVATION_ALGORITHM);
        byte[] keyBytes = keyFactory.generateSecret(keySpec).getEncoded();
        return new SecretKeySpec(keyBytes, "AES");
    } catch (GeneralSecurityException e) {
        throw new RuntimeException(e);
    }
}

private static String toBase64(byte[] bytes) {
    return Base64.encodeToString(bytes, Base64.NO_WRAP);
}

private static byte[] fromBase64(String base64) {
    return Base64.decode(base64, Base64.NO_WRAP);
}

Source

Solution 3

The problem is that with the new provider, the following snippet of code

KeyGenerator keygen = KeyGenerator.getInstance("AES");
SecureRandom secrand = SecureRandom.getInstance("SHA1PRNG");
secrand.setSeed(seed.getBytes());
keygen.init(128, secrand);
SecretKey seckey = keygen.generateKey();
byte[] rawKey = seckey.getEncoded();

generates a different, genuinely random rawKey every time it's executed. So, you're trying to decrypt with a key different from the one used to encrypt data and you get the exception. You won't be able to recover your key or data when it has been generated this way, and only the seed has been saved.

Solution 4

What fixed it for me (as @Giorgio suggested) was just replacing this:

SecureRandom secrand = SecureRandom.getInstance("SHA1PRNG");

with this:

SecureRandom secrand = SecureRandom.getInstance("SHA1PRNG", "Crypto");

Solution 5

I am unable to give you answer to your asked question but I'd simply try to work this around >- if you face some problems with bouncycastle across devices/OS version, you should ditch built-in versions completely and instead add bouncycastle as jar to your project, change your import to point to that jar, rebuild and assuming it all works you'd be immune to android built-in version changes from now on.

Solution 6

Because all of this didn't help me to generate an encrypted password which was deterministic on all android devices (>=2.1), I searched for another AES implementation. I found one which works for me on all devices. I'm not a security specialist, I'm not sure if the technique isn't as secure as it could be. I'm only posting the code for people who have run in the same problem that I had face before.

import java.security.GeneralSecurityException;
import javax.crypto.Cipher;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.SecretKeySpec;
import android.util.Log;

public class EncodeDecodeAES {


    private static final String TAG_DEBUG = "TAG";
    private IvParameterSpec ivspec;
    private SecretKeySpec keyspec;
    private Cipher cipher;

    private String iv = "fedcba9876543210";//Dummy iv (CHANGE IT!)
    private String SecretKey = "0123456789abcdef";//Dummy secretKey (CHANGE IT!)

    public EncodeDecodeAES() {
        ivspec = new IvParameterSpec(iv.getBytes());

        keyspec = new SecretKeySpec(SecretKey.getBytes(), "AES");

        try {
            cipher = Cipher.getInstance("AES/CBC/NoPadding");
        } catch (GeneralSecurityException e) {
            Log.d(TAG_DEBUG, e.getMessage());
        }
    }

    public byte[] encrypt(String text) throws Exception {
        if (text == null || text.length() == 0)
            throw new Exception("Empty string");

        byte[] encrypted = null;

        try {
            cipher.init(Cipher.ENCRYPT_MODE, keyspec, ivspec);

            encrypted = cipher.doFinal(padString(text).getBytes());
        } catch (Exception e) {
            Log.d(TAG_DEBUG, e.getMessage());
            throw new Exception("[encrypt] " + e.getMessage());
        }

        return encrypted;
    }

    public byte[] decrypt(String code) throws Exception {
        if (code == null || code.length() == 0)
            throw new Exception("Empty string");

        byte[] decrypted = null;

        try {
            cipher.init(Cipher.DECRYPT_MODE, keyspec, ivspec);

            decrypted = cipher.doFinal(hexToBytes(code));
        } catch (Exception e) {
            Log.d(TAG_DEBUG, e.getMessage());
            throw new Exception("[decrypt] " + e.getMessage());
        }
        return decrypted;
    }

    public static String bytesToHex(byte[] data) {
        if (data == null) {
            return null;
        }

        int len = data.length;
        String str = "";
        for (int i = 0; i < len; i++) {
            if ((data[i] & 0xFF) < 16)
                str = str + "0" + java.lang.Integer.toHexString(data[i] & 0xFF);
            else
                str = str + java.lang.Integer.toHexString(data[i] & 0xFF);
        }
        return str;
    }

    public static byte[] hexToBytes(String str) {
        if (str == null) {
            return null;
        } else if (str.length() < 2) {
            return null;
        } else {
            int len = str.length() / 2;
            byte[] buffer = new byte[len];
            for (int i = 0; i < len; i++) {
                buffer[i] = (byte) Integer.parseInt(str.substring(i * 2, i * 2 + 2), 16);
            }
            return buffer;
        }
    }

    private static String padString(String source) {
        char paddingChar = ' ';
        int size = 16;
        int x = source.length() % size;
        int padLength = size - x;

        for (int i = 0; i < padLength; i++) {
            source += paddingChar;
        }

        return source;
    }
}

You can use it like:

EncodeDecodeAES aes = new EncodeDecodeAES ();
/* Encrypt */
String encrypted = EncodeDecodeAES.bytesToHex(aes.encrypt("Text to Encrypt"));
/* Decrypt */
String decrypted = new String(aes.decrypt(encrypted));

Source: HERE

Solution 7

It's does have to do with the seed indeed and it's also should use multiple of 8 (like 8, 16, 24 or 32), try complete the seed with A's and B's or 1's and 0s (has to be something like this ABAB..., because AAA.. or BBB.. will not work also.) up to reach a multiple of 8 number. There is an other thing if you are reading and encrypting only bytes, (not converting it to Char64 as I did), then you need an appropriate PKCS5 or PKCS7 Padding, however in your case (due only 128bits and it's has been created with older versions of Android) PKCS5 would be enough, though you also should put it in your SecreteKeySpec something like "AES/CBC/PKCS5Padding" or "AES/ECB/PKCS5Padding" rather than just "AES", because Android 4.2 it's using PKCS7Padding as default and if it's only bytes you really need the same algorithm that was the default before. Try get a device with an Android earlier than 4.2 check the Object tree on your "keygen.init(128, secrand);" if I'm not mistaken it's has the label cipher, than use it. Give it a try.