Add linear decay function to dynamic challenges (#2347)

* Add linear decay funciton to dynamic value challenges
* Add the ability to choose between decay functions for dynamic value challenges
* Closes #2224 
* Closes #865

CTFd/plugins/dynamic_challenges/__init__.py

@@ -1,14 +1,10 @@
-from __future__ import division  # Use floating point for math calculations
-
-import math
-
 from flask import Blueprint
 
-from CTFd.models import Challenges, Solves, db
+from CTFd.models import Challenges, db
 from CTFd.plugins import register_plugin_assets_directory
 from CTFd.plugins.challenges import CHALLENGE_CLASSES, BaseChallenge
+from CTFd.plugins.dynamic_challenges.decay import DECAY_FUNCTIONS, logarithmic
 from CTFd.plugins.migrations import upgrade
-from CTFd.utils.modes import get_model
 
 
 class DynamicChallenge(Challenges):
@@ -19,6 +15,7 @@ class DynamicChallenge(Challenges):
     initial = db.Column(db.Integer, default=0)
     minimum = db.Column(db.Integer, default=0)
     decay = db.Column(db.Integer, default=0)
+    function = db.Column(db.String(32), default="logarithmic")
 
     def __init__(self, *args, **kwargs):
         super(DynamicChallenge, self).__init__(**kwargs)
@@ -51,40 +48,8 @@ class DynamicValueChallenge(BaseChallenge):
 
     @classmethod
     def calculate_value(cls, challenge):
-        Model = get_model()
-
-        solve_count = (
-            Solves.query.join(Model, Solves.account_id == Model.id)
-            .filter(
-                Solves.challenge_id == challenge.id,
-                Model.hidden == False,
-                Model.banned == False,
-            )
-            .count()
-        )
-
-        # If the solve count is 0 we shouldn't manipulate the solve count to
-        # let the math update back to normal
-        if solve_count != 0:
-            # We subtract -1 to allow the first solver to get max point value
-            solve_count -= 1
-
-        # Handle situations where admins have entered a 0 decay
-        # This is invalid as it can cause a division by zero
-        if challenge.decay == 0:
-            challenge.decay = 1
-
-        # It is important that this calculation takes into account floats.
-        # Hence this file uses from __future__ import division
-        value = (
-            ((challenge.minimum - challenge.initial) / (challenge.decay ** 2))
-            * (solve_count ** 2)
-        ) + challenge.initial
-
-        value = math.ceil(value)
-
-        if value < challenge.minimum:
-            value = challenge.minimum
+        f = DECAY_FUNCTIONS.get(challenge.function, logarithmic)
+        value = f(challenge)
 
         challenge.value = value
         db.session.commit()

CTFd/plugins/dynamic_challenges/assets/create.html

@@ -16,16 +16,36 @@
 		</small>
 	</label>
 	<input type="number" class="form-control" name="initial" placeholder="Enter value" required>
-
 </div>
 
 <div class="form-group">
-	<label for="value">Decay Limit<br>
+	<label for="value">Decay Function<br>
 		<small class="form-text text-muted">
-			The amount of solves before the challenge reaches its minimum value
+			<span>How the dynamic value will be calculated based on the Decay value</span>
+			<ul>
+				<li>Linear: Calculated as <code>Initial - (Decay * SolveCount)</code></li>
+				<li>Logarithmic: Calculated as <code>(((Minimum - Initial) / (Decay^2)) * (SolveCount^2)) + Initial</code></li>
+			</ul>
 		</small>
 	</label>
-	<input type="number" class="form-control" name="decay" min="1" placeholder="Enter decay limit" required>
+	<select name="function" class="custom-select">
+		<option value="linear">Linear</option>
+		<option value="logarithmic">Logarithmic</option>
+	</select>
+</div>
+
+<div class="form-group">
+	<label for="value">Decay<br>
+		<small class="form-text text-muted">
+			<span>The decay value is used differently depending on the above Decay Function</span>
+			<ul>
+				<li>Linear: The amount of points deducted per solve. Equal deduction per solve.</li>
+				<li>Logarithmic: The amount of solves before the challenge reaches its minimum value. Earlier solves will lose less
+					points. Later solves will lose more points</li>
+			</ul>
+		</small>
+	</label>
+	<input type="number" class="form-control" name="decay" min="1" placeholder="Enter Decay value" required>
 </div>
 
 <div class="form-group">

CTFd/plugins/dynamic_challenges/assets/update.html

@@ -20,9 +20,29 @@
 </div>
 
 <div class="form-group">
-	<label for="value">Decay Limit<br>
+	<label for="value">Decay Function<br>
 		<small class="form-text text-muted">
-			The amount of solves before the challenge reaches its minimum value
+			<span>How the dynamic value will be calculated based on the Decay value</span>
+			<ul>
+				<li>Linear: Calculated as <code>Initial - (Decay * SolveCount)</code></li>
+				<li>Logarithmic: Calculated as <code>(((Minimum - Initial) / (Decay^2)) * (SolveCount^2)) + Initial</code></li>
+			</ul>
+		</small>
+	</label>
+	<select name="function" class="custom-select">
+		<option value="linear" {% if challenge.function == "linear" %}selected{% endif %}>Linear</option>
+		<option value="logarithmic" {% if challenge.function == "logarithmic" %}selected{% endif %}>Logarithmic</option>
+	</select>
+</div>
+
+<div class="form-group">
+	<label for="value">Decay<br>
+		<small class="form-text text-muted">
+			<span>The decay value is used differently depending on the above Decay Function</span>
+			<ul>
+				<li>Linear: The amount of points deducted per solve. Equal deduction per solve.</li>
+				<li>Logarithmic: The amount of solves before the challenge reaches its minimum value. Earlier solves will lose less points. Later solves will lose more points</li>
+			</ul>
 		</small>
 	</label>
 	<input type="number" class="form-control chal-decay" min="1" name="decay" value="{{ challenge.decay }}" required>

CTFd/plugins/dynamic_challenges/decay.py

@@ -0,0 +1,75 @@
+from __future__ import division  # Use floating point for math calculations
+
+import math
+
+from CTFd.models import Solves
+from CTFd.utils.modes import get_model
+
+
+def get_solve_count(challenge):
+    Model = get_model()
+
+    solve_count = (
+        Solves.query.join(Model, Solves.account_id == Model.id)
+        .filter(
+            Solves.challenge_id == challenge.id,
+            Model.hidden == False,
+            Model.banned == False,
+        )
+        .count()
+    )
+    return solve_count
+
+
+def linear(challenge):
+    solve_count = get_solve_count(challenge)
+
+    # If the solve count is 0 we shouldn't manipulate the solve count to
+    # let the math update back to normal
+    if solve_count != 0:
+        # We subtract -1 to allow the first solver to get max point value
+        solve_count -= 1
+
+    value = challenge.initial - (challenge.decay * solve_count)
+
+    value = math.ceil(value)
+
+    if value < challenge.minimum:
+        value = challenge.minimum
+
+    return value
+
+
+def logarithmic(challenge):
+    solve_count = get_solve_count(challenge)
+
+    # If the solve count is 0 we shouldn't manipulate the solve count to
+    # let the math update back to normal
+    if solve_count != 0:
+        # We subtract -1 to allow the first solver to get max point value
+        solve_count -= 1
+
+    # Handle situations where admins have entered a 0 decay
+    # This is invalid as it can cause a division by zero
+    if challenge.decay == 0:
+        challenge.decay = 1
+
+    # It is important that this calculation takes into account floats.
+    # Hence this file uses from __future__ import division
+    value = (
+        ((challenge.minimum - challenge.initial) / (challenge.decay ** 2))
+        * (solve_count ** 2)
+    ) + challenge.initial
+
+    value = math.ceil(value)
+
+    if value < challenge.minimum:
+        value = challenge.minimum
+
+    return value
+
+
+DECAY_FUNCTIONS = {
+    "linear": linear,
+    "logarithmic": logarithmic,
+}

CTFd/plugins/dynamic_challenges/migrations/eb68f277ab61_add_func_column_to_dynamic_challenges.py

@@ -0,0 +1,28 @@
+"""Add func column to dynamic_challenges
+
+Revision ID: eb68f277ab61
+Revises: 9e6f6578ca84
+Create Date: 2023-06-28 17:37:48.244827
+
+"""
+import sqlalchemy as sa
+
+# revision identifiers, used by Alembic.
+revision = "eb68f277ab61"
+down_revision = "b37fb68807ea"
+branch_labels = None
+depends_on = None
+
+
+def upgrade(op=None):
+    op.add_column(
+        "dynamic_challenge", sa.Column("function", sa.String(length=32), nullable=True)
+    )
+    conn = op.get_bind()
+    conn.execute(
+        "UPDATE dynamic_challenge SET function = 'logarithmic' WHERE function IS NULL"
+    )
+
+
+def downgrade(op=None):
+    op.drop_column("dynamic_challenge", "function")

tests/challenges/test_dynamic.py

@@ -349,3 +349,54 @@ def test_dynamic_challenges_reset():
         assert DynamicChallenge.query.count() == 0
 
     destroy_ctfd(app)
+
+
+def test_dynamic_challenge_linear_loses_value_properly():
+    app = create_ctfd(enable_plugins=True)
+    with app.app_context():
+        register_user(app)
+        client = login_as_user(app, name="admin", password="password")
+
+        challenge_data = {
+            "name": "name",
+            "category": "category",
+            "description": "description",
+            "function": "linear",
+            "initial": 100,
+            "decay": 5,
+            "minimum": 1,
+            "state": "visible",
+            "type": "dynamic",
+        }
+
+        r = client.post("/api/v1/challenges", json=challenge_data)
+        assert r.get_json().get("data")["id"] == 1
+
+        gen_flag(app.db, challenge_id=1, content="flag")
+
+        for i, team_id in enumerate(range(2, 26)):
+            name = "user{}".format(team_id)
+            email = "user{}@examplectf.com".format(team_id)
+            # We need to bypass rate-limiting so gen_user instead of register_user
+            user = gen_user(app.db, name=name, email=email)
+            user_id = user.id
+
+            with app.test_client() as client:
+                # We need to bypass rate-limiting so creating a fake user instead of logging in
+                with client.session_transaction() as sess:
+                    sess["id"] = user_id
+                    sess["nonce"] = "fake-nonce"
+                    sess["hash"] = hmac(user.password)
+
+                data = {"submission": "flag", "challenge_id": 1}
+                r = client.post("/api/v1/challenges/attempt", json=data)
+                resp = r.get_json()["data"]
+                assert resp["status"] == "correct"
+
+                chal = DynamicChallenge.query.filter_by(id=1).first()
+
+                if i >= 20:
+                    assert chal.value == chal.minimum
+                else:
+                    assert chal.value == (chal.initial - (i * 5))
+    destroy_ctfd(app)