Have set_keys take signature_participants, not removed_participants

Now no one is removed from the DKG. Only `t` people publish the key however.

Uses a BitVec for an efficient encoding of the participants.

substrate/abi/Cargo.toml

@@ -16,8 +16,10 @@ rustdoc-args = ["--cfg", "docsrs"]
 workspace = true
 
 [dependencies]
-scale = { package = "parity-scale-codec", version = "3", default-features = false, features = ["derive"] }
-scale-info = { version = "2", default-features = false, features = ["derive"] }
+bitvec = { version = "1", default-features = false, features = ["alloc", "serde"] }
+
+scale = { package = "parity-scale-codec", version = "3", default-features = false, features = ["derive", "bit-vec"] }
+scale-info = { version = "2", default-features = false, features = ["derive", "bit-vec"] }
 
 borsh = { version = "1", default-features = false, features = ["derive", "de_strict_order"], optional = true }
 serde = { version = "1", default-features = false, features = ["derive", "alloc"], optional = true }
@@ -39,6 +41,8 @@ serai-signals-primitives = { path = "../signals/primitives", version = "0.1", de
 
 [features]
 std = [
+  "bitvec/std",
+
   "scale/std",
   "scale-info/std",
 

substrate/abi/src/validator_sets.rs

@@ -11,8 +11,8 @@ use serai_validator_sets_primitives::*;
 pub enum Call {
   set_keys {
     network: NetworkId,
-    removed_participants: BoundedVec<SeraiAddress, ConstU32<{ MAX_KEY_SHARES_PER_SET / 3 }>>,
     key_pair: KeyPair,
+    signature_participants: bitvec::vec::BitVec<u8, bitvec::order::Lsb0>,
     signature: Signature,
   },
   set_embedded_elliptic_curve_key {

substrate/client/Cargo.toml

@@ -20,6 +20,8 @@ workspace = true
 zeroize = "^1.5"
 thiserror = { version = "1", optional = true }
 
+bitvec = { version = "1", default-features = false, features = ["alloc", "serde"] }
+
 hex = "0.4"
 scale = { package = "parity-scale-codec", version = "3" }
 serde = { version = "1", features = ["derive"], optional = true }

substrate/client/src/serai/validator_sets.rs

@@ -181,17 +181,14 @@ impl<'a> SeraiValidatorSets<'a> {
 
   pub fn set_keys(
     network: NetworkId,
-    removed_participants: sp_runtime::BoundedVec<
-      SeraiAddress,
-      sp_core::ConstU32<{ primitives::MAX_KEY_SHARES_PER_SET / 3 }>,
-    >,
     key_pair: KeyPair,
+    signature_participants: bitvec::vec::BitVec<u8, bitvec::order::Lsb0>,
     signature: Signature,
   ) -> Transaction {
     Serai::unsigned(serai_abi::Call::ValidatorSets(serai_abi::validator_sets::Call::set_keys {
       network,
-      removed_participants,
       key_pair,
+      signature_participants,
       signature,
     }))
   }

substrate/runtime/src/abi.rs

@@ -103,16 +103,13 @@ impl From<Call> for RuntimeCall {
       Call::ValidatorSets(vs) => match vs {
         serai_abi::validator_sets::Call::set_keys {
           network,
-          removed_participants,
           key_pair,
+          signature_participants,
           signature,
         } => RuntimeCall::ValidatorSets(validator_sets::Call::set_keys {
           network,
-          removed_participants: <_>::try_from(
-            removed_participants.into_iter().map(PublicKey::from).collect::<Vec<_>>(),
-          )
-          .unwrap(),
           key_pair,
+          signature_participants,
           signature,
         }),
         serai_abi::validator_sets::Call::set_embedded_elliptic_curve_key {
@@ -289,14 +286,11 @@ impl TryInto<Call> for RuntimeCall {
         _ => Err(())?,
       }),
       RuntimeCall::ValidatorSets(call) => Call::ValidatorSets(match call {
-        validator_sets::Call::set_keys { network, removed_participants, key_pair, signature } => {
+        validator_sets::Call::set_keys { network, key_pair, signature_participants, signature } => {
           serai_abi::validator_sets::Call::set_keys {
             network,
-            removed_participants: <_>::try_from(
-              removed_participants.into_iter().map(SeraiAddress::from).collect::<Vec<_>>(),
-            )
-            .unwrap(),
             key_pair,
+            signature_participants,
             signature,
           }
         }

substrate/validator-sets/pallet/Cargo.toml

@@ -19,10 +19,11 @@ ignored = ["scale", "scale-info"]
 workspace = true
 
 [dependencies]
+bitvec = { version = "1", default-features = false, features = ["alloc", "serde"] }
 hashbrown = { version = "0.14", default-features = false, features = ["ahash", "inline-more"] }
 
-scale = { package = "parity-scale-codec", version = "3", default-features = false, features = ["derive"] }
-scale-info = { version = "2", default-features = false, features = ["derive"] }
+scale = { package = "parity-scale-codec", version = "3", default-features = false, features = ["derive", "bit-vec"] }
+scale-info = { version = "2", default-features = false, features = ["derive", "bit-vec"] }
 
 serde = { version = "1", default-features = false, features = ["derive", "alloc"] }
 
@@ -48,6 +49,8 @@ dex-pallet = { package = "serai-dex-pallet", path = "../../dex/pallet", default-
 
 [features]
 std = [
+  "bitvec/std",
+
   "scale/std",
   "scale-info/std",
 

substrate/validator-sets/pallet/src/lib.rs

@@ -927,14 +927,15 @@ pub mod pallet {
     pub fn set_keys(
       origin: OriginFor<T>,
       network: NetworkId,
-      removed_participants: BoundedVec<Public, ConstU32<{ MAX_KEY_SHARES_PER_SET / 3 }>>,
       key_pair: KeyPair,
+      signature_participants: bitvec::vec::BitVec<u8, bitvec::order::Lsb0>,
       signature: Signature,
     ) -> DispatchResult {
       ensure_none(origin)?;
 
       // signature isn't checked as this is an unsigned transaction, and validate_unsigned
       // (called by pre_dispatch) checks it
+      let _ = signature_participants;
       let _ = signature;
 
       let session = Self::session(network).unwrap();
@@ -949,15 +950,6 @@ pub mod pallet {
         Self::set_total_allocated_stake(network);
       }
 
-      // This does not remove from TotalAllocatedStake or InSet in order to:
-      // 1) Not decrease the stake present in this set. This means removed participants are
-      //    still liable for the economic security of the external network. This prevents
-      //    a decided set, which is economically secure, from falling below the threshold.
-      // 2) Not allow parties removed to immediately deallocate, per commentary on deallocation
-      //    scheduling (https://github.com/serai-dex/serai/issues/394).
-      for removed in removed_participants {
-        Self::deposit_event(Event::ParticipantRemoved { set, removed });
-      }
       Self::deposit_event(Event::KeyGen { set, key_pair });
 
       Ok(())
@@ -1070,7 +1062,7 @@ pub mod pallet {
     fn validate_unsigned(_: TransactionSource, call: &Self::Call) -> TransactionValidity {
       // Match to be exhaustive
       match call {
-        Call::set_keys { network, ref removed_participants, ref key_pair, ref signature } => {
+        Call::set_keys { network, ref key_pair, ref signature_participants, ref signature } => {
           let network = *network;
 
           // Don't allow the Serai set to set_keys, as they have no reason to do so
@@ -1094,30 +1086,24 @@ pub mod pallet {
           // session on this assumption
           assert_eq!(Pallet::<T>::latest_decided_session(network), Some(current_session));
 
-          // This does not slash the removed participants as that'll be done at the end of the
-          // set's lifetime
-          let mut removed = hashbrown::HashSet::new();
-          for participant in removed_participants {
-            // Confirm this wasn't duplicated
-            if removed.contains(&participant.0) {
-              Err(InvalidTransaction::Custom(2))?;
-            }
-            removed.insert(participant.0);
-          }
-
           let participants =
             Participants::<T>::get(network).expect("session existed without participants");
 
+          // Check the bitvec is of the proper length
+          if participants.len() != signature_participants.len() {
+            Err(InvalidTransaction::Custom(2))?;
+          }
+
           let mut all_key_shares = 0;
           let mut signers = vec![];
           let mut signing_key_shares = 0;
-          for participant in participants {
+          for (participant, in_use) in participants.into_iter().zip(signature_participants) {
             let participant = participant.0;
             let shares = InSet::<T>::get(network, participant)
               .expect("participant from Participants wasn't InSet");
             all_key_shares += shares;
 
-            if removed.contains(&participant.0) {
+            if !in_use {
               continue;
             }
 
@@ -1135,9 +1121,7 @@ pub mod pallet {
           // Verify the signature with the MuSig key of the signers
           // We theoretically don't need set_keys_message to bind to removed_participants, as the
           // key we're signing with effectively already does so, yet there's no reason not to
-          if !musig_key(set, &signers)
-            .verify(&set_keys_message(&set, removed_participants, key_pair), signature)
-          {
+          if !musig_key(set, &signers).verify(&set_keys_message(&set, key_pair), signature) {
             Err(InvalidTransaction::BadProof)?;
           }
 

substrate/validator-sets/primitives/src/lib.rs

@@ -99,12 +99,8 @@ pub fn musig_key(set: ValidatorSet, set_keys: &[Public]) -> Public {
 }
 
 /// The message for the set_keys signature.
-pub fn set_keys_message(
-  set: &ValidatorSet,
-  removed_participants: &[Public],
-  key_pair: &KeyPair,
-) -> Vec<u8> {
-  (b"ValidatorSets-set_keys", set, removed_participants, key_pair).encode()
+pub fn set_keys_message(set: &ValidatorSet, key_pair: &KeyPair) -> Vec<u8> {
+  (b"ValidatorSets-set_keys", set, key_pair).encode()
 }
 
 pub fn report_slashes_message(set: &ValidatorSet, slashes: &[(Public, u32)]) -> Vec<u8> {