KeyStoreWrapper.kt

@TargetApi(23)
fun createAndroidKeyStoreSymmetricKey(alias: String): SecretKey {
    val keyGenerator = KeyGenerator.getInstance(KeyProperties.KEY_ALGORITHM_AES, "AndroidKeyStore")
    val builder = KeyGenParameterSpec.Builder(alias, KeyProperties.PURPOSE_ENCRYPT or KeyProperties.PURPOSE_DECRYPT)
            .setBlockModes(KeyProperties.BLOCK_MODE_CBC)
            .setEncryptionPaddings(KeyProperties.ENCRYPTION_PADDING_PKCS7)
    keyGenerator.init(builder.build())
    return keyGenerator.generateKey()
}

fun getAndroidKeyStoreSymmetricKey(alias: String): SecretKey? = keyStore.getKey(alias, null) as SecretKey?