Just an apointment: TinyDB has a problem: any user can see what does any TinyDB stores if they have root access to the mobilephone. I’ve made some tests and finally I reached an XML file where TinyDB stores the data, and any user will be able to use it as they want. (I’m not going to share the path to the file for obvious reasons)
So, I recommend to store values in TinyDB with an encrypt method, like AES-128 that uses any key that you want, like 123456 or abcdef or something like that, or use any other encryption method that could be decrypted with a key, not like MD5 or BASE64