Android KeyStore Initialization

Question

First off I am new to android Programming, though I am not new to programming itself. What I am, essentially, trying to do is to save my encryption Keys into the Android Keystore. There seems to be a phenomenal lack of such information on GOOGLE, itself. Since there is not much how-to available on the topic I am assuming that it isn't fairly standard knowledge. So can someone please give me a sample code to

1. Initialize the KeyStore(Will be using AES-256).
2. Save multiple keys in a KeyStore(Please tell me the max number of keys I can store in 1 KeyStore, since i plan on saving nothing short of a 100).
3. Get Keys from KeyStore.
4. Edit Keys
5. Delete Keys
6. Delete Entire KeyStore

So in essence a code for all basic functions of a keystore. Thank you in advance for your assistance.

Answer 1

If you set your minSdkVersion to 23 or higher Android M makes it easy to generate and manage symmetric keys as of this month.

Check out the 4th example listed here. https://developer.android.com/reference/android/security/keystore/KeyGenParameterSpec.html

 KeyGenerator keyGenerator = KeyGenerator.getInstance(
         KeyProperties.KEY_ALGORITHM_AES, "AndroidKeyStore");
 keyGenerator.initialize(
         new KeyGenParameterSpec.Builder("key2",
                 KeyProperties.PURPOSE_ENCRYPT | KeyProperties.PURPOSE_DECRYPT)
                 .setBlockModes(KeyProperties.BLOCK_MODE_GCM)
                 .setEncryptionPaddings(KeyProperties.ENCRYPTION_PADDING_NONE)
                 .build());
 SecretKey key = keyGenerator.generateKey();

 Cipher cipher = Cipher.getInstance("AES/GCM/NoPadding");
 cipher.init(Cipher.ENCRYPT_MODE, key);
 ...

 // The key can also be obtained from the Android Keystore any time as follows:
 KeyStore keyStore = KeyStore.getInstance("AndroidKeyStore");
 keyStore.load(null);
 key = (SecretKey) keyStore.getKey("key2", null);

This example also was helpful. https://github.com/googlesamples/android-ConfirmCredential/blob/master/Application/src/main/java/com/example/android/confirmcredential/MainActivity.java

Answer 2

I think Android Key Store does not support symmetric keys like AES keys. Please refer to here. BTW, why does the app need so many symmetric keys? I suggest that you store one master asymmetric key in key store, and use this key to encrypt many other symmetric keys in your app. Hope you solve your problem soon.