feat: rotate signed pre-key on a cadence (WA Web RotateKeyJob)

src/client.rs

@@ -550,6 +550,9 @@ pub struct Client {
 
     /// Prevents concurrent prekey upload operations (matches WA Web's dedup set in `handlePreKeyLow`).
     pub(crate) prekey_upload_lock: Arc<async_lock::Mutex<()>>,
+    /// Single-flights signed pre-key rotation so overlapping post-login tasks
+    /// (from reconnect churn) can't run the rotate/upload/prune flow concurrently.
+    pub(crate) signed_pre_key_rotation_lock: Arc<async_lock::Mutex<()>>,
     /// Notifier for when offline sync (ib offline stanza) is received.
     /// WhatsApp Web waits for this before sending passive tasks (prekey upload, active IQ, presence).
     pub(crate) offline_sync_notifier: Arc<event_listener::Event>,

src/client/lifecycle.rs

@@ -217,6 +217,7 @@ impl Client {
             initial_keys_synced_notifier: Arc::new(event_listener::Event::new()),
             initial_app_state_keys_received: Arc::new(AtomicBool::new(false)),
             prekey_upload_lock: Arc::new(async_lock::Mutex::new(())),
+            signed_pre_key_rotation_lock: Arc::new(async_lock::Mutex::new(())),
             offline_sync_notifier: Arc::new(event_listener::Event::new()),
             offline_sync_completed: Arc::new(AtomicBool::new(false)),
             offline_sync_finish_started: Arc::new(AtomicBool::new(false)),

src/client/node_io.rs

@@ -749,6 +749,30 @@ impl Client {
                 warn!("Failed to upload pre-keys during startup: {e:?}");
             }
 
+            // WA Web RotateKeyJob: rotate the signed pre-key on its cadence.
+            // Spawned so a slow or failing encrypt IQ never delays the rest of
+            // post-login init.
+            check_generation!();
+            let rotate_client = client_clone.clone();
+            let rotate_generation = task_generation;
+            client_clone
+                .runtime
+                .spawn(Box::pin(async move {
+                    // A newer connection may have taken over between spawn and now;
+                    // rotating on a stale generation would upload a duplicate key.
+                    if rotate_client.connection_generation.load(Ordering::SeqCst)
+                        != rotate_generation
+                    {
+                        return;
+                    }
+                    if let Err(e) = rotate_client.maybe_rotate_signed_pre_key().await
+                        && !rotate_client.is_shutting_down()
+                    {
+                        warn!("Signed pre-key rotation check failed: {e:?}");
+                    }
+                }))
+                .detach();
+
             // === Send active IQ ===
             // The server sends <ib><offline count="X"/></ib> AFTER we exit passive mode.
             // This matches WhatsApp Web's behavior: executePassiveTasks() -> sendPassiveModeProtocol("active")

src/features/mod.rs

@@ -15,6 +15,7 @@ mod polls;
 mod presence;
 mod profile;
 mod reaction;
+mod rotate_key;
 mod signal;
 pub(crate) mod status;
 mod tctoken;

src/features/rotate_key.rs

@@ -0,0 +1,292 @@
+//! Signed pre-key rotation, mirroring WhatsApp Web's `RotateKeyJob`.
+//!
+//! The signed pre-key minted at pairing is otherwise permanent. WA Web
+//! periodically generates a fresh one, uploads it via an `encrypt` IQ, and
+//! retains the old ones so prekey messages already in flight against a
+//! previous signed pre-key still decrypt.
+
+use crate::client::Client;
+use crate::request::IqError;
+use buffa::Message;
+use wacore::iq::prekeys::RotateSignedPreKeySpec;
+use wacore::libsignal::protocol::{KeyPair, PrivateKey, PublicKey};
+use wacore::libsignal::store::record_helpers::new_signed_pre_key_record;
+use wacore::store::commands::DeviceCommand;
+use waproto::whatsapp::SignedPreKeyRecordStructure;
+
+/// Rotation cadence. This is the one value NOT grounded in the WA Web bundle
+/// (there it is a persisted background job with a server-tuned schedule), so
+/// treat it as a policy default that is safe to tune.
+pub(crate) const SIGNED_PRE_KEY_ROTATION_INTERVAL_MS: i64 = 7 * 24 * 60 * 60 * 1000; // weekly
+
+/// Total signed pre-keys kept addressable: the current key (device field) plus
+/// the RETENTION-1 most recent rotated-out keys in the backend table. Bounds
+/// the decrypt window for delayed prekey messages built against a rotated key.
+pub(crate) const SIGNED_PRE_KEY_RETENTION: usize = 3;
+
+/// 24-bit ceiling, matching the one-time prekey id border. Ids advance by one
+/// per rotation and wrap back to 1 here.
+const MAX_SIGNED_PRE_KEY_ID: u32 = 16_777_215;
+
+/// Whether the cadence has elapsed. `last == 0` means the field predates this
+/// feature; the baseline path handles that, so we never rotate on `0`.
+pub(crate) fn should_rotate_signed_pre_key(last_rotation_ms: i64, now_ms: i64) -> bool {
+    last_rotation_ms != 0
+        && now_ms.saturating_sub(last_rotation_ms) >= SIGNED_PRE_KEY_ROTATION_INTERVAL_MS
+}
+
+/// Next id = current + 1, wrapping at the 24-bit border back to 1.
+pub(crate) fn next_signed_pre_key_id(current: u32) -> u32 {
+    if current >= MAX_SIGNED_PRE_KEY_ID {
+        1
+    } else {
+        current + 1
+    }
+}
+
+impl Client {
+    /// Rotate the signed pre-key if the cadence has elapsed. Seeds the cadence
+    /// baseline (without rotating) for devices upgraded in with the field at 0.
+    pub(crate) async fn maybe_rotate_signed_pre_key(&self) -> Result<(), anyhow::Error> {
+        // Single-flight: a concurrent rotation (e.g. an older post-login task
+        // racing a newer one across reconnect churn) already covers this cadence,
+        // so skip rather than run the rotate/upload/prune flow twice.
+        let Some(_guard) = self.signed_pre_key_rotation_lock.try_lock() else {
+            return Ok(());
+        };
+
+        let last = self
+            .persistence_manager
+            .get_device_snapshot()
+            .last_signed_pre_key_rotation_ms;
+        let now = wacore::time::now_millis();
+
+        if last == 0 {
+            self.persistence_manager
+                .process_command(DeviceCommand::SetSignedPreKeyRotationBaseline(now))
+                .await;
+            self.persistence_manager
+                .flush()
+                .await
+                .map_err(|e| anyhow::anyhow!("failed to flush rotation baseline: {e:?}"))?;
+            return Ok(());
+        }
+
+        if should_rotate_signed_pre_key(last, now) {
+            self.rotate_signed_pre_key().await?;
+        }
+        Ok(())
+    }
+
+    /// Stage a fresh signed pre-key durably, upload it, and only on server
+    /// acceptance promote it locally: retain the outgoing key, advance the
+    /// current key + cadence, and prune to [`SIGNED_PRE_KEY_RETENTION`].
+    ///
+    /// Both the new candidate and the outgoing key are written to the backend
+    /// table *before* upload (the candidate reused verbatim on retry), so every
+    /// partial failure is safe: whatever the server ends up advertising, we hold
+    /// its private key, and the old id's decrypt window survives regardless. An
+    /// ambiguous transport error (the server may have accepted `new_id`) leaves
+    /// the staged key decryptable via the load fallback; a definitive rejection
+    /// just leaves the current key in place to retry — never advancing the
+    /// cadence or pruning the key the server still hands out. A single-flight
+    /// lock ([`maybe_rotate_signed_pre_key`]) keeps overlapping tasks from
+    /// racing this sequence.
+    pub(crate) async fn rotate_signed_pre_key(&self) -> Result<(), anyhow::Error> {
+        let snapshot = self.persistence_manager.get_device_snapshot();
+        let now = wacore::time::now_millis();
+        let backend = self.persistence_manager.backend();
+
+        let old_id = snapshot.signed_pre_key_id;
+        let new_id = next_signed_pre_key_id(old_id);
+
+        // Stage the candidate before upload, reusing an already-staged one for
+        // this id verbatim. A retry after an ambiguous failure then re-uploads
+        // THIS exact key instead of minting a fresh one under the same id, so the
+        // key the server may already have accepted is never overwritten/lost.
+        let (new_kp, signature) = match backend
+            .load_signed_prekey(new_id)
+            .await
+            .map_err(|e| anyhow::anyhow!("failed to load staged signed pre-key: {e}"))?
+        {
+            Some(bytes) => {
+                let s = SignedPreKeyRecordStructure::decode_from_slice(&bytes)
+                    .map_err(|e| anyhow::anyhow!("staged signed pre-key decode: {e}"))?;
+                let public = PublicKey::from_djb_public_key_bytes(
+                    s.public_key
+                        .as_deref()
+                        .ok_or_else(|| anyhow::anyhow!("staged signed pre-key missing public"))?,
+                )?;
+                let private =
+                    PrivateKey::deserialize(s.private_key.as_deref().ok_or_else(|| {
+                        anyhow::anyhow!("staged signed pre-key missing private")
+                    })?)?;
+                let signature: [u8; 64] = s
+                    .signature
+                    .ok_or_else(|| anyhow::anyhow!("staged signed pre-key missing signature"))?
+                    .try_into()
+                    .map_err(|_| anyhow::anyhow!("staged signature must be 64 bytes"))?;
+                (KeyPair::new(public, private), signature)
+            }
+            None => {
+                let mut rng = rand::make_rng::<rand::rngs::StdRng>();
+                let kp = KeyPair::generate(&mut rng);
+                // Sign the new public with the identity private key over the
+                // serialized (not raw) public bytes, matching Device::new().
+                let signature: [u8; 64] = snapshot
+                    .identity_key
+                    .private_key
+                    .calculate_signature(&kp.public_key.serialize(), &mut rng)?
+                    .as_ref()
+                    .try_into()
+                    .map_err(|_| anyhow::anyhow!("Ed25519 signature must be 64 bytes"))?;
+                let record =
+                    new_signed_pre_key_record(new_id, &kp, signature, wacore::time::now_utc());
+                backend
+                    .store_signed_prekey(new_id, &record.encode_to_vec())
+                    .await
+                    .map_err(|e| anyhow::anyhow!("failed to stage new signed pre-key: {e}"))?;
+                (kp, signature)
+            }
+        };
+
+        // Retain the outgoing key BEFORE upload, so once the server accepts the
+        // new key the old id's decrypt window is already durable — no
+        // post-acceptance write can strand it. Required: on failure we abort
+        // before sending anything, leaving the current key fully intact to retry.
+        let old_record = new_signed_pre_key_record(
+            old_id,
+            &snapshot.signed_pre_key,
+            snapshot.signed_pre_key_signature,
+            wacore::time::now_utc(),
+        );
+        backend
+            .store_signed_prekey(old_id, &old_record.encode_to_vec())
+            .await
+            .map_err(|e| anyhow::anyhow!("failed to retain old signed pre-key: {e}"))?;
+
+        // WA Web reads 406 = bad key, 409 = server validation fail, >=500 =
+        // transient; none warrant hard-failing login or advancing local state.
+        // On any failure the staged candidate stays put for the next retry.
+        match self
+            .execute(RotateSignedPreKeySpec::new(
+                new_id,
+                new_kp.public_key,
+                signature.to_vec(),
+            ))
+            .await
+        {
+            Ok(()) => {}
+            Err(IqError::ServerError { code, text, .. }) => {
+                // A 4xx (WA Web 406 = bad key, 409 = validation fail) is a
+                // deterministic rejection of THIS key: the server did not accept
+                // it, so reusing the staged candidate would wedge rotation
+                // forever. Drop it so the next attempt mints a fresh one. A 5xx
+                // is transient — keep the staged key and reuse it later.
+                let discard = code < 500;
+                if discard && let Err(e) = backend.remove_signed_prekey(new_id).await {
+                    log::warn!("failed to drop rejected staged signed pre-key {new_id}: {e}");
+                }
+                log::warn!(
+                    "signed pre-key rotation upload rejected (code={code}, text='{text}'); \
+                     {}, will retry on a later connect",
+                    if discard {
+                        "discarded the rejected key"
+                    } else {
+                        "keeping the staged key"
+                    }
+                );
+                return Ok(());
+            }
+            Err(e) => {
+                // Ambiguous transport failure: the server may have accepted the
+                // key, so keep the staged candidate and reuse it on retry.
+                log::warn!(
+                    "signed pre-key rotation upload failed: {e:?}; \
+                     keeping the staged key, will retry on a later connect"
+                );
+                return Ok(());
+            }
+        }
+
+        // Server accepted new_id, and both the old (retained) and new (staged)
+        // keys are already durable, so promotion cannot strand either.
+        self.persistence_manager
+            .process_command(DeviceCommand::SetSignedPreKey {
+                key_pair: new_kp,
+                id: new_id,
+                signature,
+                rotation_ms: now,
+            })
+            .await;
+        self.persistence_manager
+            .flush()
+            .await
+            .map_err(|e| anyhow::anyhow!("failed to flush rotated signed pre-key: {e:?}"))?;
+
+        // new_id now lives in the device field, so drop its redundant staged copy
+        // before pruning to RETENTION total addressable keys (field + RETENTION-1
+        // rotated-out). Numeric ordering is safe: ids advance one per rotation, so
+        // the wrap at MAX is ~300k years out.
+        if let Err(e) = backend.remove_signed_prekey(new_id).await {
+            log::warn!("failed to drop staged signed pre-key {new_id}: {e}");
+        }
+        let mut retained = backend
+            .load_all_signed_prekeys()
+            .await
+            .map_err(|e| anyhow::anyhow!("failed to load retained signed pre-keys: {e}"))?;
+        retained.sort_unstable_by_key(|(id, _)| std::cmp::Reverse(*id));
+        for (id, _) in retained
+            .into_iter()
+            .skip(SIGNED_PRE_KEY_RETENTION.saturating_sub(1))
+        {
+            if let Err(e) = backend.remove_signed_prekey(id).await {
+                log::warn!("failed to prune retained signed pre-key {id}: {e}");
+            }
+        }
+
+        Ok(())
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn should_rotate_truth_table() {
+        // last == 0 never rotates (baseline path owns it).
+        assert!(!should_rotate_signed_pre_key(0, i64::MAX));
+
+        let last = 1_000_000_000_000;
+        // Just before the interval: no rotation.
+        assert!(!should_rotate_signed_pre_key(
+            last,
+            last + SIGNED_PRE_KEY_ROTATION_INTERVAL_MS - 1
+        ));
+        // Exactly at the boundary: rotate.
+        assert!(should_rotate_signed_pre_key(
+            last,
+            last + SIGNED_PRE_KEY_ROTATION_INTERVAL_MS
+        ));
+        // Well past: rotate.
+        assert!(should_rotate_signed_pre_key(
+            last,
+            last + SIGNED_PRE_KEY_ROTATION_INTERVAL_MS * 3
+        ));
+        // Clock skew backwards: saturating_sub yields 0, no rotation.
+        assert!(!should_rotate_signed_pre_key(last, last - 1));
+    }
+
+    #[test]
+    fn next_id_increments_and_wraps() {
+        assert_eq!(next_signed_pre_key_id(1), 2);
+        assert_eq!(next_signed_pre_key_id(41), 42);
+        assert_eq!(
+            next_signed_pre_key_id(MAX_SIGNED_PRE_KEY_ID - 1),
+            MAX_SIGNED_PRE_KEY_ID
+        );
+        // At and beyond the 24-bit border, wrap back to 1.
+        assert_eq!(next_signed_pre_key_id(MAX_SIGNED_PRE_KEY_ID), 1);
+    }
+}