Tag Archives: Carrier Privileges

Simple trick to increase coverage: Lying to users about signal strength

Mobile Networks, , ,

Poking around in Android the other day I found this nugget in Carrier Config manager; a flag (KEY_INFLATE_SIGNAL_STRENGTH_BOOL) to always report the signal strength to the user as one bar higher than it really is.

It’s not documented in the Android docs, but it’s there in the source available for any operator to use.

Notably both AT&T and Verizon have this flag enabled on their networks, I’m not sure who was responsible for requesting this to be added to Android, nor could I find it in the git-blame, but we can see it in the CarrierConfig which contains all the network settings for each of these operators.

Operators are always claiming to have the biggest coverage or the best network, but stuff like this, along with the fake 5G flags, don’t help build trust, especially considering the magic mobile phone antennas which negate the need for all this deception anyway.

Android Carrier Privileges

GSM, IMS / VoLTE, LTE, Mobile Networks, SDM, Software, , ,

So a problem had arisen, carriers wanted to change certain carrier related settings on devices (Specifically the Carrier Config Manager) in the Android ecosystem. The Android maintainers didn’t want to open the permissions to change these settings to everyone, only the carrier providing service to that device.

And if you purchased a phone from Carrier A, and moved to Carrier B, how do you manage the permissions for Carrier B’s app and then restrict Carrier A’s app?

Enter the Android UICC Carrier Privileges.

The carrier loads a certificate onto the SIM Cards, and signing Android Apps with this certificate, allowing the Android OS to verify the certificate on the card and the App are known to each other, and thus the carrier issuing the SIM card also issued the app, and presto, the permissions are granted to the app.

Carriers have full control of the UICC, so this mechanism provides a secure and flexible way to manage apps from the mobile network operator (MNO) hosted on generic app distribution channels (such as Google Play) while retaining special privileges on devices and without the need to sign apps with the per-device platform certificate or preinstall as a system app.

UICC Carrier Privileges doc

Once these permissions are granted your app is able to make API calls related to:

  • APN Settings
  • Roaming/nonroaming networks
  • Visual voicemail
  • SMS/MMS network settings
  • VoLTE/IMS configurations
  • OTA Updating SIM Cards
  • Sending PDUs to the card