Dissecting “The Blob” with free software


Smartphones, watches, IOT devices, even home appliances and cars often require their owners to download opaque binary blobs (files containing data, code or both) from online servers. For developers willing to understand how these devices work, it’s often like fighting “The Blob” creature in the horror movie from a few decades ago.

Kaitai web ide ( https://ide.kaitai.io/ ) is a GPLv3 web application that allows to upload binary files and analyse them in the browser.
Further it allows to describe the structure in a document (with a custom syntax). These documents may also be used to build parsers in several programming languages.

During the talk we will explore some of the features of kaitai web ide as used in the development of the Gadgetbridge project. A group of developers succeeded in understanding the format of the “xtra2.bin” file (which is used to assist the GPS chip on android phones to get a position fix faster). This is the first step to achieve uploading A-GPS data to wearable devices with embedded GPS chips with a complete free-software toolchain.