core_crypto/mls/conversation/
commit_delay.rs

1use log::{debug, trace};
2use openmls::prelude::LeafNodeIndex;
3
4use super::MlsConversation;
5use crate::MlsError;
6
7/// These constants intend to ramp up the delay and flatten the curve for later positions
8const DELAY_RAMP_UP_MULTIPLIER: f32 = 120.0;
9const DELAY_RAMP_UP_SUB: u64 = 106;
10const DELAY_POS_LINEAR_INCR: u64 = 15;
11const DELAY_POS_LINEAR_RANGE: std::ops::RangeInclusive<u64> = 1..=3;
12
13impl MlsConversation {
14    /// Helps consumer by providing a deterministic delay in seconds for him to commit its pending proposal.
15    /// It depends on the index of the client in the ratchet tree
16    /// * `self_index` - ratchet tree index of self client
17    /// * `epoch` - current group epoch
18    /// * `nb_members` - number of clients in the group
19    pub fn compute_next_commit_delay(&self) -> Option<u64> {
20        use openmls::messages::proposals::Proposal;
21
22        if self.group.pending_proposals().count() > 0 {
23            let removed_index = self
24                .group
25                .pending_proposals()
26                .filter_map(|proposal| {
27                    if let Proposal::Remove(remove_proposal) = proposal.proposal() {
28                        Some(remove_proposal.removed())
29                    } else {
30                        None
31                    }
32                })
33                .collect::<Vec<LeafNodeIndex>>();
34
35            let self_index = self.group.own_leaf_index();
36            debug!(removed_index:? = removed_index, self_index:? = self_index; "Indexes");
37            // Find a remove proposal that concerns us
38            let is_self_removed = removed_index.iter().any(|&i| i == self_index);
39
40            // If our own client has been removed, don't commit
41            if is_self_removed {
42                debug!("Self removed from group, no delay needed");
43                return None;
44            }
45
46            let epoch = self.group.epoch().as_u64();
47            let mut own_index = self.group.own_leaf_index().u32() as u64;
48
49            // Look for members that were removed at the left of our tree in order to shift our own leaf index (post-commit tree visualization)
50            let left_tree_diff = self
51                .group
52                .members()
53                .take(own_index as usize)
54                .try_fold(0u32, |mut acc, kp| {
55                    if removed_index.contains(&kp.index) {
56                        acc += 1;
57                    }
58
59                    Result::<_, MlsError>::Ok(acc)
60                })
61                .unwrap_or_default();
62
63            // Post-commit visualization of the number of members after remove proposals
64            let nb_members = (self.group.members().count() as u64).saturating_sub(removed_index.len() as u64);
65            // This shifts our own leaf index to the left (tree-wise) from as many as there was removed members that have a smaller leaf index than us (older members)
66            own_index = own_index.saturating_sub(left_tree_diff as u64);
67
68            Some(Self::calculate_delay(own_index, epoch, nb_members))
69        } else {
70            trace!("No pending proposals, no delay needed");
71            None
72        }
73    }
74
75    fn calculate_delay(self_index: u64, epoch: u64, nb_members: u64) -> u64 {
76        let position = if nb_members > 0 {
77            ((epoch % nb_members) + (self_index % nb_members)) % nb_members + 1
78        } else {
79            1
80        };
81
82        if DELAY_POS_LINEAR_RANGE.contains(&position) {
83            position.saturating_sub(1) * DELAY_POS_LINEAR_INCR
84        } else {
85            (((position as f32).ln() * DELAY_RAMP_UP_MULTIPLIER) as u64).saturating_sub(DELAY_RAMP_UP_SUB)
86        }
87    }
88}
89
90#[cfg(test)]
91mod tests {
92    use super::*;
93    use crate::test_utils::*;
94    use tls_codec::Serialize as _;
95    use wasm_bindgen_test::*;
96
97    wasm_bindgen_test_configure!(run_in_browser);
98
99    #[test]
100    #[wasm_bindgen_test]
101    fn calculate_delay_single() {
102        let (self_index, epoch, nb_members) = (0, 0, 1);
103        let delay = MlsConversation::calculate_delay(self_index, epoch, nb_members);
104        assert_eq!(delay, 0);
105    }
106
107    #[test]
108    #[wasm_bindgen_test]
109    fn calculate_delay_max() {
110        let (self_index, epoch, nb_members) = (u64::MAX, u64::MAX, u64::MAX);
111        let delay = MlsConversation::calculate_delay(self_index, epoch, nb_members);
112        assert_eq!(delay, 0);
113    }
114
115    #[test]
116    #[wasm_bindgen_test]
117    fn calculate_delay_min() {
118        let (self_index, epoch, nb_members) = (u64::MIN, u64::MIN, u64::MAX);
119        let delay = MlsConversation::calculate_delay(self_index, epoch, nb_members);
120        assert_eq!(delay, 0);
121    }
122
123    #[test]
124    #[wasm_bindgen_test]
125    fn calculate_delay_zero_members() {
126        let (self_index, epoch, nb_members) = (0, 0, u64::MIN);
127        let delay = MlsConversation::calculate_delay(self_index, epoch, nb_members);
128        assert_eq!(delay, 0);
129    }
130
131    #[test]
132    #[wasm_bindgen_test]
133    fn calculate_delay_min_max() {
134        let (self_index, epoch, nb_members) = (u64::MIN, u64::MAX, u64::MAX);
135        let delay = MlsConversation::calculate_delay(self_index, epoch, nb_members);
136        assert_eq!(delay, 0);
137    }
138
139    #[test]
140    #[wasm_bindgen_test]
141    fn calculate_delay_n() {
142        let epoch = 1;
143        let nb_members = 10;
144
145        let indexes_delays = [
146            (0, 15),
147            (1, 30),
148            (2, 60),
149            (3, 87),
150            (4, 109),
151            (5, 127),
152            (6, 143),
153            (7, 157),
154            (8, 170),
155            (9, 0),
156            // wrong but it shouldn't cause problems
157            (10, 15),
158        ];
159
160        for (self_index, expected_delay) in indexes_delays {
161            let delay = MlsConversation::calculate_delay(self_index, epoch, nb_members);
162            assert_eq!(delay, expected_delay);
163        }
164    }
165
166    #[apply(all_cred_cipher)]
167    #[wasm_bindgen_test]
168    async fn calculate_delay_creator_removed(case: TestContext) {
169        let [alice_central, bob_central, charlie_central] = case.sessions().await;
170        Box::pin(async move {
171            let id = conversation_id();
172
173            alice_central
174                .transaction
175                .new_conversation(&id, case.credential_type, case.cfg.clone())
176                .await
177                .unwrap();
178
179            let bob = bob_central.rand_key_package(&case).await;
180            alice_central
181                .transaction
182                .conversation(&id)
183                .await
184                .unwrap()
185                .add_members(vec![bob])
186                .await
187                .unwrap();
188            let bob_welcome = alice_central.mls_transport().await.latest_welcome_message().await;
189            assert_eq!(alice_central.get_conversation_unchecked(&id).await.members().len(), 2);
190
191            bob_central
192                .transaction
193                .process_welcome_message(bob_welcome.clone().into(), case.custom_cfg())
194                .await
195                .unwrap();
196
197            let charlie = charlie_central.rand_key_package(&case).await;
198            alice_central
199                .transaction
200                .conversation(&id)
201                .await
202                .unwrap()
203                .add_members(vec![charlie])
204                .await
205                .unwrap();
206            let charlie_welcome_bundle = alice_central.mls_transport().await.latest_commit_bundle().await;
207            assert_eq!(alice_central.get_conversation_unchecked(&id).await.members().len(), 3);
208
209            let _ = bob_central
210                .transaction
211                .conversation(&id)
212                .await
213                .unwrap()
214                .decrypt_message(&charlie_welcome_bundle.commit.tls_serialize_detached().unwrap())
215                .await
216                .unwrap();
217
218            charlie_central
219                .transaction
220                .process_welcome_message(charlie_welcome_bundle.welcome.unwrap().into(), case.custom_cfg())
221                .await
222                .unwrap();
223
224            assert_eq!(
225                bob_central.get_conversation_unchecked(&id).await.id(),
226                alice_central.get_conversation_unchecked(&id).await.id()
227            );
228            assert_eq!(
229                charlie_central.get_conversation_unchecked(&id).await.id(),
230                alice_central.get_conversation_unchecked(&id).await.id()
231            );
232
233            let proposal_bundle = alice_central
234                .transaction
235                .new_remove_proposal(&id, alice_central.get_client_id().await)
236                .await
237                .unwrap();
238
239            let bob_hypothetical_position = 0;
240            let charlie_hypothetical_position = 1;
241
242            let bob_decrypted_message = bob_central
243                .transaction
244                .conversation(&id)
245                .await
246                .unwrap()
247                .decrypt_message(&proposal_bundle.proposal.tls_serialize_detached().unwrap())
248                .await
249                .unwrap();
250
251            assert_eq!(
252                bob_decrypted_message.delay,
253                Some(DELAY_POS_LINEAR_INCR * bob_hypothetical_position)
254            );
255
256            let charlie_decrypted_message = charlie_central
257                .transaction
258                .conversation(&id)
259                .await
260                .unwrap()
261                .decrypt_message(&proposal_bundle.proposal.tls_serialize_detached().unwrap())
262                .await
263                .unwrap();
264
265            assert_eq!(
266                charlie_decrypted_message.delay,
267                Some(DELAY_POS_LINEAR_INCR * charlie_hypothetical_position)
268            );
269        })
270        .await;
271    }
272}