Decrypt string in java which in encrypted in android app

Question

I am using this class to encrypt a string in android app

public class Encryption {
     public static String encrypt(String seed, String cleartext) throws Exception {
            byte[] rawKey = getRawKey(seed.getBytes());
            byte[] result = encrypt(rawKey, cleartext.getBytes());
            return toHex(result);
        }

        public static String decrypt(String seed, String encrypted) throws Exception {
            byte[] rawKey = getRawKey(seed.getBytes());
            byte[] enc = toByte(encrypted);
            byte[] result = decrypt(rawKey, enc);
            return new String(result);
        }

        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;
        }

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

        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));
        }
}

I am using above class like this -

Encryption.encrypt("password", "some text to be encrypted");

Their is no problem in encrypting the string, but when i try to decrypt the encrypted string (using the same class i posted above) in external java program (not in android app),

Encryption.decrypt("password","D4036388D459C4009812FB3F1AE4BB36E4419C97775D");

i get this exception -

javax.crypto.BadPaddingException: Given final block not properly padded
    at com.sun.crypto.provider.SunJCE_f.b(DashoA13*..)
    at com.sun.crypto.provider.SunJCE_f.b(DashoA13*..)
    at com.sun.crypto.provider.AESCipher.engineDoFinal(DashoA13*..)
    at javax.crypto.Cipher.doFinal(DashoA13*..)
    at Encryption.decrypt(Encryption.java:59)
    at Encryption.decrypt(Encryption.java:32)
    at Encryption.main(Encryption.java:96)

I think, this is because i am using same code on different platforms,

But i don't know proper reason why this doesn't work ? and Is their any way i can decrypt the string in java?

Joop Eggen · Accepted Answer · 2013-05-31 19:48:54Z

1

@SteveP is probably right.

Still another problem I see, is the byte[] getBytes("UTF-8") (binary data) to String new String(bytes, "UTF-8") (text) conversion. On Android the default encoding is UTF-8, on Windows most likely something else.

answered May 31, 2013 at 19:48

Joop Eggen

110k8 gold badges89 silver badges142 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

Decrypt string in java which in encrypted in android app

1 Answer 1

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related