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TODO - the Solon Backlog, if you will

In this file we try to list the various areas where new contributors can find tasks to work on. Tasks are categorized by topic, and ordered roughly in the sequence they need to be implemented.

The dummy backend

While the current dummy backend is just a mockup, and the intent is to now focus on implementing the real thing with the cryptographic functionality from the Acquisti paper, there are a few things that would make sense to still implement in the dummy backend in order to demonstrate a complete data flow.

  • Currently one major Liquid Feedback feature is still missing from the Solon dummy backend: Delegation of your vote per unit or per area. (Per issue delegation is implemented.)
  • For issues in state=closed, show voting results also in the Solon dummy UI. (Now results just go into LQFB and can be seen there with a LQFB frontend.)
  • You can grep the code for "TODO" to see if there's something else that could be done.


The tasks in this list do not require any mathematic wizardry, but are quite important. Some of them will require constant help, so if you are looking to become a long-time contributor, feel free to pick one of these as your own.

  • We urgently need automated testing / unit testing. Note that partially this has to be testing the HTML interface too, not just unit testing of python functions.
  • Keeping the patch in liquid_feedback_patch/ up to date against new versions of Liquid Feedback Core.
  • Create an easy installation script of Solon (one step + configuration)
  • To be honest, Liquid Feedback itself is a pain to install. It would help many people if you want to simplify that.
  • If you can think of items to add to this list, that is helpful in itself...

High-level architecture

For a high-level architecture, see:

The Acquisti algorithm relies on a group of servers, each operated by an independent Voting Authority, to communicate together. Threshold cryptography. Also see next section about the bulleting board. It's all group communication.

Clients of course need to be under full control of their end users / voters - this is the same as for using any other crypto. Hence the client cannot simply be a web page, it needs to be some form of app/executable run on the client side.

Helios Voting

After launching Solon, we became aware of a an open source project by Ben Adida that implements a simple homomorphic e-voting algorithm:

The next step for Solon will now be to integrate Helios as an e-voting backend (instead of the current dummy backend). No work on this has started yet.

To read up on Helios, it makes sense to start with the original 2008 paper:

Then download the code, get it running, and figure out how to create a ballot and vote via Solon.

The Non-erasable Public Bulletin Board

Homomorphic e-voting algorithms typically rely on an abstract device known a non-erasable public bulletin board. The Helios Voting software is a simplified approach and ignores this requirement. (They focus on guaranteeing voter verifiability, while knowingly compromising a little bit on voter anonymity / security in order to keep things simple.) While we intend to focus on Helios integration first, eventually we expect to also build an implementation of such a non-erasable public bulletin board:

Chaum [Cha81] introduced the concept of a bulletin board, a public broadcast 
channel with memory where a party may write information that any party may 
read. Since then, bulletin boards have been often used in election schemes. 
All communications with the bulletin board are public and therefore can be 
monitored. In the application we consider, no party can erase any data. 

While such an element has been commonly used in cryptography for over 30 years now, papers typically leave undefined how to actually implement such a magic bulletin board.

Since homomorphic e-voting commonly is based on threshold cryptography among a group of independent voting authorities, it seems like an obvious idea to also implement the non-erasable board as some form of distributed storage among a cluster of servers, each of which is run by one of the authorities. This could be implemented either with a message queue or some form of group communication library:

  • Allowed operations are insert and read. Update and delete are specifically not allowed.
  • A message is received by the bulletin board when a majority/threshold of the nodes in the cluster acknowledge receipt of it.
  • Clients probably need to read from multiple / majority of nodes to verify that they get the correct message on read. In fact they also need to verify that an inserted message was correctly inserted.

Implementing this bulletin board is a nice non-trivial task that still doesn't include any cryptography.