# Firmware Over The Air The firmware update is critical since its alteration back to compromise the entire system. It is therefore necessary to take appropriate protective measures. AGL includes the _meta-updater_ Yocto layer that enables OTA software updates via [Uptane](https://uptane.github.io), an automotive-specific extension to [The Update Framework](https://theupdateframework.github.io/). Uptane and TUF are open standards that define a secure protocol for delivering and verifying updates even when the servers and network--internet and car-internal--aren't fully trusted. _meta-updater_ includes the application [`aktualizr`](https://github.com/advancedtelematic/aktualizr), developed Advanced Telematic Systems (now part of HERE Technologies) that enables OTA for an ECU. `aktualizr` combined with Uptane is suitable for updating the firmware, software, and other packages on even functionally critical ECUs. `aktualizr` can be enabled with the free, open souce backend [`ota-community-edition`](https://github.com/advancedtelematic/ota-community-edition). This FOTA update mechanism can be enabled through the `agl-sota` feature. ## Building To build an AGL image that uses `aktualizr`, the following can be used. ``` source meta-agl/scripts/aglsetup.sh -m agl-sota ``` During the build, _meta-updater_ will use credentials downloaded from `ota-community-edition` to sign metadata verifying the build as authentic. These signatures are part of the Uptane framework and are used to verify FOTA updates. ## Atomic Upgrades with Rollbacks `aktualizr`'s primary method of updating firmware is to use `libostree` with binary diffs. The binary diffs use the least amout of bandwidth, and by it's nature `libostree` stores current and previous firmware versions on disk or in flash memory to allow for rollbacks. `libostree` is a content addressable object store much like `git`. Versions are specified via SHA2-256. These hashes are signed in the Uptane metadata and are robust against cryptographic compromise.