feat(elections): Pseudonimize votes after tallying

elections/migrations/0034_vote_pseudonymous_user_alter_vote_user.py

@@ -0,0 +1,25 @@
+# Generated by Django 4.2.12 on 2024-07-11 12:01
+
+from django.conf import settings
+from django.db import migrations, models
+import django.db.models.deletion
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('elections', '0033_inactive_users'),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name='vote',
+            name='pseudonymous_user',
+            field=models.CharField(blank=True, max_length=16),
+        ),
+        migrations.AlterField(
+            model_name='vote',
+            name='user',
+            field=models.ForeignKey(null=True, on_delete=django.db.models.deletion.CASCADE, to=settings.AUTH_USER_MODEL),
+        ),
+    ]

elections/migrations/0035_auto_20240711_1424.py

@@ -0,0 +1,44 @@
+# Generated by Django 4.2.12 on 2024-07-11 12:24
+
+import random
+
+from django.db import migrations
+
+alphabet = "abcdefghjkmnopqrstuvwxyzABCDEFGHJKLMNPQRSTUVWXYZ23456789"
+
+
+def generate_password(size):
+    random.seed()
+
+    return "".join(random.choice(alphabet) for _ in range(size))
+
+
+def pseudonymize_users(apps, _):
+    Question = apps.get_model("elections", "Question")
+    Vote = apps.get_model("elections", "Vote")
+
+    votes = set()
+
+    for q in Question.objects.filter(election__tallied=True).prefetch_related(
+        "options__vote_set"
+    ):
+
+        for v in q.voters.all():
+            pseudonym = generate_password(16)
+
+            for opt in q.options.all():
+                for vote in opt.vote_set.filter(user=v):
+                    vote.pseudonymous_user = pseudonym
+                    vote.user = None
+                    votes.add(vote)
+
+    Vote.objects.bulk_update(votes, ["pseudonymous_user", "user"])
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ("elections", "0034_vote_pseudonymous_user_alter_vote_user"),
+    ]
+
+    operations = [migrations.RunPython(pseudonymize_users)]

elections/models.py

@@ -10,6 +10,7 @@ from django.template.loader import render_to_string
 from django.utils.translation import gettext_lazy as _
 
 from shared.auth import CONNECTION_METHODS
+from shared.auth.utils import generate_password
 from shared.json import Serializer
 from shared.utils import choices_length
 
@@ -141,6 +142,26 @@ class Question(Serializer, models.Model):
         tally_function = getattr(TallyFunctions, TALLY_FUNCTIONS[self.type])
         tally_function(self)
 
+    @transaction.atomic
+    def pseudonymize(self):
+        """
+        Generates a random id for each voter
+        """
+
+        options = list(self.options.prefetch_related("vote_set"))
+        votes: set[Vote] = set()
+
+        for v in self.voters.all():
+            pseudonym = generate_password(16)
+
+            for opt in options:
+                for vote in opt.vote_set.filter(user=v):
+                    vote.pseudonymous_user = pseudonym
+                    vote.user = None
+                    votes.add(vote)
+
+        Vote.objects.bulk_update(votes, ["pseudonymous_user", "user"])
+
     @property
     def results(self) -> str:
         return render_to_string(
@@ -172,6 +193,8 @@ class Question(Serializer, models.Model):
 
 
 class Option(Serializer, models.Model):
+    vote_set: models.Manager["Vote"]
+
     question = models.ForeignKey(
         Question, related_name="options", on_delete=models.CASCADE
     )
@@ -210,7 +233,10 @@ class Option(Serializer, models.Model):
 
 class Vote(models.Model):
     option = models.ForeignKey(Option, on_delete=models.CASCADE)
-    user = models.ForeignKey(settings.AUTH_USER_MODEL, on_delete=models.CASCADE)
+    user = models.ForeignKey(
+        settings.AUTH_USER_MODEL, on_delete=models.CASCADE, null=True
+    )
+    pseudonymous_user = models.CharField(max_length=16, blank=True)
 
     class Meta:
         ordering = ["option"]
@@ -219,6 +245,9 @@ class Vote(models.Model):
 class RankedVote(Vote):
     rank: "Rank"
 
+    class Meta:
+        abstract = True
+
 
 class Rank(models.Model):
     vote = models.OneToOneField(Vote, on_delete=models.CASCADE)

elections/tasks.py

@@ -10,3 +10,11 @@ def send_election_mail(election_pk: int, subject: str, body: str, reply_to: str)
     send_mail(election, subject, body, reply_to)
     election.sent_mail = True
     election.save(update_fields=["sent_mail"])
+
+
+@background
+def pseudonimize_election(election_pk: int):
+    election = Election.objects.get(pk=election_pk)
+
+    for q in election.questions.all():
+        q.pseudonymize()

elections/utils.py

@@ -301,16 +301,16 @@ class BallotsData:
         """Renvoie un tableau affichant les options sélectionnées pour chaque bulletin"""
         from .models import Vote
 
-        votes = Vote.objects.filter(option__question=question).select_related("user")
+        votes = Vote.objects.filter(option__question=question)
 
         options = list(question.options.all())
 
         ballots = {}
         for v in votes:
-            ballot = ballots.get(v.user, [False] * len(options))
+            ballot = ballots.get(v.pseudonymous_user, [False] * len(options))
             ballot[options.index(v.option)] = True
 
-            ballots[v.user] = ballot
+            ballots[v.pseudonymous_user] = ballot
 
         return render_to_string(
             "elections/ballots/select.html",
@@ -323,13 +323,13 @@ class BallotsData:
         from .models import Rank
 
         options = list(question.options.all())
-        ranks = Rank.objects.select_related("vote__user").filter(
+        ranks = Rank.objects.select_related("vote").filter(
             vote__option__in=options
         )
         ranks_by_user = {}
 
         for r in ranks:
-            user = r.vote.user
+            user = r.vote.pseudonymous_user
             if user in ranks_by_user:
                 ranks_by_user[user].append(r.rank)
             else:

elections/views.py

@@ -41,13 +41,14 @@ from .mixins import (
 )
 from .models import Election, Option, Question, Vote
 from .staticdefs import MAIL_VOTE_DELETED, MAIL_VOTERS, QUESTION_TYPES, VOTE_RULES
-from .tasks import send_election_mail
+from .tasks import pseudonimize_election, send_election_mail
 from .utils import create_users
 
 if TYPE_CHECKING:
     from elections.typing import User
 else:
     from django.contrib.auth import get_user_model
+
     User = get_user_model()
 
 # TODO: access control *everywhere*
@@ -299,6 +300,9 @@ class ElectionTallyView(ClosedElectionMixin, BackgroundUpdateView):
         election.tallied = True
         election.time_tallied = timezone.now()
         election.save()
+
+        pseudonimize_election(election.pk)
+
         return super().get(request, *args, **kwargs)