Little-Brosers Week 2: Walking into the unknown

Hello, this is the Little Brosers group. This will be the only post from our group this week as we have all worked collectively on the same subjects until now.


As you may have heard from other groups, the focus of this week was establishing PSSCs (Project Specific Success Criteria), cutting the big project into small digest pieces, and putting deadlines on them. We now have a better view of the road ahead of us, and it was both exciting and a little scary to quantify the amount of work this project will represent for the four of us.


We decide to class our PSSCs into four categories:


  • Algorithmic category, whose aim is to define precisely the protocol followed when a smartphone encounters a drop. The big steps are going to be the “handshake” and authentication, determining which message is missing to each entity, and finally the transfer of said messages.
  • Hardware dependant category, which regroups everything relating the PCB directly: schematics, test of each component, software closely related to hardware (OTA firmware update for example) …
  • Back-end category, which obviously concerns the main server which will act as our certification authority for users, our main tool to synchronize the dates of the drops and prevent a maximum amount of date cheating from users with malicious intents, and finally as a “main drop” connected to the internet to help synchronize messages.
  • App category, which is very important even though it is not the main focus of the project. These PSSCs will help ensure we do not forget to work on the specific aspects of a smartphone app while we are all very busy thinking about the rest.


Here is a link to the wiki of our repo, where you will find the exhaustive and up to date list of our PSSCs, which are obviously going to change in the next few days as we apply the feedback we’ve received after presenting them. You will also find a link to the presentation we gave on friday.


Next week, a few tasks await us. First, precising the theoric aspect of the exchange protocol between the drop and the smartphone. We are going to look for resources about hashing, Merkle trees and symmetrical/asymmetrical cryptography, and try to put on paper a first “pseudo-code” version of our protocol. Second, we are also going to have to put numbers on our needs for the project PCB, to further narrow down the component selection. In our case, we will have to find ways to discriminate the various BLE chips that we have spotted, as well as decide on what external flash we want. And last but not least, as mentioned earlier, we are also going to update the PSSCs to add a few things we have forgotten and correct a few mistakes in the planning.


Thank you all for reading, and see you next week !

The Little Brosers team

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