ESME uses both a Local and Master PIN/ Password.
When the App is first installed you are required to set a PIN or Password.
This PIN / Password is encrypted and stored locally, a hashed identifier is also sent via SMS to the ESME registration service, this is stored along side the number you are registering from.
At this point ESME will check to ensure that the phone number being registered from is either a new unknown number, or if previously registered that the same PIN / Password and registered number combination is again being used to set up the app.
If the PIN/ Password is not the same the app setup process will fail. This is to stop someone either uninstalling or reinstalling the ESME app to reset the pin and be able to un-encrypt the ESME messages if any any still valid of course.
Assuming the initial setup goes well, This initial process sets both local and master pins the same. The local pin is used to access and decrypt the sms messages locally, these can be set independently from each other within the settings section of the app.
You can also use your bio metric fingerprint scanner if your phone supports it, to login and decrypt you messages locally.