End-user flow: Using Human Trustees App
In Electa, the trustees play a vital role in two key processes of the election event, using pieces of a cryptographic key. The first process corresponds to the threshold ceremony, which happens before any voting can happen – in a way, this ceremony marks the start of the election. The second process corresponds to the results ceremony, that is, when voting is concluded, and the results need to be generated.
In this guide, you can find a detailed walkthrough on how to use the Trustee app for both ceremonies, as well as explanations of the different steps that make up the threshold and results ceremonies.
Below you can find a pdf version of this guide, which you can download and share with your trustees.
General notes on the Trustee App
For both of the processes mentioned above, you, as a trustee, will be required to use the Trustee app. To do so, start by downloading the app here. Note that you should always use the latest version of the application that is available.
The trustee app allows you to register as a trustee and reconnect to an election (if you already are a registered trustee) in order to proceed with the relevant ceremonies. Additionally, the app supports different languages, which you can change from the three lines in the top-right corner.
The threshold ceremony takes place before any voting happens, and includes the following steps:
In the first step, trustees receive an invitation code, which they input into the app to generate the first part of their cryptographic key – this is then saved in a file locally.
After that, a threshold of trustees is set by the election admin.
Once this threshold is met, the cryptographic process starts. This process generates the election encryption key and each trustee’s share of the decryption key.
Finally, partial keys (private shares of the decryption key) are distributed per trustee, and the threshold ceremony is finalized.
1.1. Connect to election
First, the trustees receive an email containing an invitation code to become a trustee in the election. From this email, trustees can begin to register as a trustee.
Open the Trustee app and click “Register as trustee”. This will redirect you to the following page:
Insert the invitation code you received via email in the textbox field. See below an example of an email:
Click “Connect and choose location“ and select where you want to save the trustee-key file on your local device (eg. a laptop).
This will now connect you to the election.
1.2. Setting the threshold
The election admin will proceed to the next step of the threshold ceremony, which is setting up the minimum requirements of attending trustees – this threshold is composed of both system and human trustees.
1.3. Cryptographic process
Once this threshold is met, that is, the minimum number of trustees required to be connected to the election, the cryptographic process can begin. This process is composed of different cryptographic procedures (which you can follow along in the Trustee app as well):
Generating polynomial coefficients means creating random numbers that determine how each trustee’s share of the secret key is split and verified.
Generating and sending partial secrets means computing and privately sharing the fragments of each trustee’s polynomial, so everyone has what they need.
Computing local decryption key means calculating each trustee’s personal share of the overall decryption key, using the received partial secrets.
Together, these procedures generate a public encryption key and each trustee’s private share of the decryption key, which will be essential for the results ceremony.
1.4. End of threshold ceremony
This process will be rather quick, and once finalized, the threshold ceremony is also finished, and the election can proceed.
Once the ceremony is finished, you can close the application and take a backup of your trustee file before closing the device. It is your responsibility to ensure that a backup file is copied correctly to an external device – see best practices for the trustee file below. Please compare the contents of the file (e.g, through a text editor program) to confirm that the backup file is identical to the original file. Failing to provide an intact trustee file may result in the election results being unable to be extracted.
Best Practices: Trustee File
When you receive the invitation email to register as a trustee, make sure to copy the entire invitation code exactly as it is.
Once you have successfully registered as a trustee, you will be given a trustee file – you should not share the file with anyone, as this is a private file. This file should be stored safely and privately, as it contains the trustee’s cryptographic identity.
If you wish to save the trustee-key file in a remote device, such as a USB stick, make sure to only do that after the registration process is done to avoid failure to save the file properly.
You can inspect the file to ensure it contains all the items needed (see below how the file should look)
Make sure to save the file in a safe location on your device – and preferably a place where you will not lose it or forget about it.
Additionally, the file should only be saved as a “.trustee-key” format – if for some reason it saves in a different format, it will not work.
Be aware of how you name the file, so that you can remember it when you need it.
The results ceremony takes place when the voting is concluded. It corresponds to the process of generating results, encompassed by the crucial steps of mixing, decrypting, and aggregating.
Before starting the results ceremony, you need to be connected to the Trustee app.
Reconnecting to the app
Open the Trustee app once again and now click on “Existing Trustee”.
Now you will need to locate your trustee-key file (which you stored in your local device in Step 2). Click “Browse for trustee-key file to connect“ and choose your trustee-key file.
You will be able to see the location of the selected file.
Proceed to click “Reconnect“.
Once connected to the election, you can follow the election progress. Inside the app, it is possible to see all ballots that exist currently in the election, and whether they are in progress or not, as well as the number of trustees that are presently connected.
Generating results
To generate results, all needed trustees need to have the app open and be connected to the election. As the results extraction starts, the progress can be followed step-by-step in the app. Below, you can see the progression of the result generation process.
Mixing: this is the process of shuffling all encrypted votes many times so that nobody can tell which encrypted vote came from which voter.
Decrypting: once the votes have been mixed so they’re anonymous, the trustees work together to decrypt the votes, using their shares of the decryption key
Aggregating: finally, during the aggregation step, all decrypted votes are counted in order to get the election results.
The results will only be presented in Electa’s backend. However, the election admin may choose to make them visible to the trustees, and the results will then appear in the Trustee app.