Encrypt and Decrypt with AES ECB mode 'BadPaddingException' in some cases

Question

In android/java app

   public static void setKey(String myKey) {

        MessageDigest sha = null;
        try {
            key = new byte[]{(byte) '5', (byte) 'F', (byte) '8', (byte) 'p', (byte) 'J', (byte) 't', (byte) 'v', (byte) 'U', (byte) 'm', (byte) 'q', (byte) 'k', (byte) '7', (byte) 'A', (byte) 'M', (byte) 'v', (byte) 'b', (byte) 'q', (byte) 'o', (byte) 'H', (byte) 'M', (byte) '9', (byte) 'a', (byte) 'p', (byte) '4', (byte) '9', (byte) 'm', (byte) 'c', (byte) 'u', (byte) 'u', (byte) '5', (byte) 'B', (byte) 'X'};
            System.out.println(new String(key, "UTF-8"));
            secretKey = new SecretKeySpec(key, "AES");
        } catch (UnsupportedEncodingException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }


    public static String encrypt(String strToEncrypt) {
        try {
            Cipher cipher = Cipher.getInstance("AES/ECB/PKCS5Padding");
            cipher.init(Cipher.ENCRYPT_MODE, secretKey);
            setEncryptedarr(cipher.doFinal(strToEncrypt.getBytes("UTF-8")));
            setEncryptedString(String.valueOf(Base64.encode(cipher.doFinal(strToEncrypt.getBytes("UTF-8")), Base64.DEFAULT)));
            //setEncryptedString(Base64.encodeBase64String(cipher.doFinal(strToEncrypt.getBytes("UTF-8"))));
        } catch (Exception e) {
            e.printStackTrace();
            System.out.println("Error while encrypting: " + e.toString());
        }
        return null;
    }

    public static String decryptbyte(byte[] strToDecrypt) {
        try {
            Cipher cipher = Cipher.getInstance("AES/ECB/PKCS5PADDING");
            cipher.init(Cipher.DECRYPT_MODE, secretKey);
            setDecryptedarr(cipher.doFinal(strToDecrypt));
            System.out.println("encrypt : decropted size : " + getDecryptedarr().length);
            setDecryptedString(new String(cipher.doFinal(strToDecrypt)));
        } catch (Exception e) {
            System.out.println("Error wnhile decrypting: " + e.toString());
            e.printStackTrace();
        }
        return null;
    }

    public static String decrypt(String strToDecrypt) {
        try {
            Cipher cipher = Cipher.getInstance("AES/ECB/PKCS5PADDING");
            cipher.init(Cipher.DECRYPT_MODE, secretKey);
            setDecryptedarr(cipher.doFinal(Base64.decode(strToDecrypt, Base64.DEFAULT)));
            setDecryptedString(new String(cipher.doFinal(Base64.decode(strToDecrypt, Base64.DEFAULT))));

        } catch (Exception e) {
            e.printStackTrace();
            System.out.println("Error while decrypting: " + e.toString());

        }
        return null;
    }

I am working on this code : http://aesencryption.net/ I use this snipped code is working well when use it in case of : encryptbyte and decryptbyte whitch take byte[] and I test it it's result of encryption in this site http://aesencryption.net/

but i need it to decript data came from server (response is came string) and when I convert the String to byte[] the code always thraw exception : javax.crypto.IllegalBlockSizeException: error:0606506D:digital envelope routines:EVP_DecryptFinal_ex:wrong final block length**

I think it's when covert the String to byte[] it change , if that what is the right way to convert . Advice please .

This code thraw exception :

try {
    AES.setKey("");
    final String strToDecrypt = "tATTXSdXI4w0oiu/fzgpyA==";
    AES.decryptbyte(toBytes(strToDecrypt.toCharArray()));
} catch (Exception ex) {
    ex.printStackTrace();
}

this is the exception

01-21 15:24:55.861 15700-15700/ W/System.err: javax.crypto.IllegalBlockSizeException: error:0606506D:digital envelope routines:EVP_DecryptFinal_ex:wrong final block length
01-21 15:24:55.861 15700-15700/ W/System.err:     at com.android.org.conscrypt.NativeCrypto.EVP_CipherFinal_ex(Native Method)
01-21 15:24:55.861 15700-15700/ W/System.err:     at com.android.org.conscrypt.OpenSSLCipher.doFinalInternal(OpenSSLCipher.java:430)
01-21 15:24:55.861 15700-15700/ W/System.err:     at com.android.org.conscrypt.OpenSSLCipher.engineDoFinal(OpenSSLCipher.java:466)
01-21 15:24:55.861 15700-15700/ W/System.err:     at javax.crypto.Cipher.doFinal(Cipher.java:1340)
 01-21 15:24:55.861 15700-15700/ W/System.err:     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1118)
01-21 15:24:55.861 15700-15700/ W/System.err:     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2648)
01-21 15:24:55.861 15700-15700/ W/System.err:     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2769)
01-21 15:24:55.861 15700-15700/ W/System.err:     at android.app.ActivityThread.access$900(ActivityThread.java:177)
01-21 15:24:55.861 15700-15700/ W/System.err:     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1430)
01-21 15:24:55.861 15700-15700/ W/System.err:     at android.os.Handler.dispatchMessage(Handler.java:102)
01-21 15:24:55.861 15700-15700/ W/System.err:     at android.os.Looper.loop(Looper.java:135)
01-21 15:24:55.861 15700-15700/ W/System.err:     at android.app.ActivityThread.main(ActivityThread.java:5910)
01-21 15:24:55.861 15700-15700/ W/System.err:     at java.lang.reflect.Method.invoke(Native Method)
01-21 15:24:55.861 15700-15700/ W/System.err:     at java.lang.reflect.Method.invoke(Method.java:372)
01-21 15:24:55.861 15700-15700/ W/System.err:     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1405)
01-21 15:24:55.861 15700-15700/ W/System.err:     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1200)

Answer 1

The final bit of code: strToDecrypt = "tATTXSdXI4w0oiu/fzgpyA==" seems to have a base64 encoding, notice the trailing == characters. This makes sense since encryption is data byte oriented, not string oriented.

Base64 "tATTXSdXI4w0oiu/fzgpyA=="
hexadecimal: B404D35D2757238C34A22BBF7F3829C8 (16 bytes).

You need to decode the Base64 to data bytes for the code:

AES.setKey("");
final String strToDecrypt = "tATTXSdXI4w0oiu/fzgpyA==";
AES.decryptbyte(toBytes(strToDecrypt.toCharArray()));

Also note that the above code has an empty string for a key, that is an error.