One Round DKG (#589)

* Upstream GBP, divisor, circuit abstraction, and EC gadgets from FCMP++

* Initial eVRF implementation

Not quite done yet. It needs to communicate the resulting points and proofs to
extract them from the Pedersen Commitments in order to return those, and then
be tested.

* Add the openings of the PCs to the eVRF as necessary

* Add implementation of secq256k1

* Make DKG Encryption a bit more flexible

No longer requires the use of an EncryptionKeyMessage, and allows pre-defined
keys for encryption.

* Make NUM_BITS an argument for the field macro

* Have the eVRF take a Zeroizing private key

* Initial eVRF-based DKG

* Add embedwards25519 curve

* Inline the eVRF into the DKG library

Due to how we're handling share encryption, we'd either need two circuits or to
dedicate this circuit to the DKG. The latter makes sense at this time.

* Add documentation to the eVRF-based DKG

* Add paragraph claiming robustness

* Update to the new eVRF proof

* Finish routing the eVRF functionality

Still needs errors and serialization, along with a few other TODOs.

* Add initial eVRF DKG test

* Improve eVRF DKG

Updates how we calculcate verification shares, improves performance when
extracting multiple sets of keys, and adds more to the test for it.

* Start using a proper error for the eVRF DKG

* Resolve various TODOs

Supports recovering multiple key shares from the eVRF DKG.

Inlines two loops to save 2**16 iterations.

Adds support for creating a constant time representation of scalars < NUM_BITS.

* Ban zero ECDH keys, document non-zero requirements

* Implement eVRF traits, all the way up to the DKG, for secp256k1/ed25519

* Add Ristretto eVRF trait impls

* Support participating multiple times in the eVRF DKG

* Only participate once per key, not once per key share

* Rewrite processor key-gen around the eVRF DKG

Still a WIP.

* Finish routing the new key gen in the processor

Doesn't touch the tests, coordinator, nor Substrate yet.
`cargo +nightly fmt && cargo +nightly-2024-07-01 clippy --all-features -p serai-processor`
does pass.

* Deduplicate and better document in processor key_gen

* Update serai-processor tests to the new key gen

* Correct amount of yx coefficients, get processor key gen test to pass

* Add embedded elliptic curve keys to Substrate

* Update processor key gen tests to the eVRF DKG

* 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.

* Update the coordinator binary for the new DKG

This does not yet update any tests.

* Add sensible Debug to key_gen::[Processor, Coordinator]Message

* Have the DKG explicitly declare how to interpolate its shares

Removes the hack for MuSig where we multiply keys by the inverse of their
lagrange interpolation factor.

* Replace Interpolation::None with Interpolation::Constant

Allows the MuSig DKG to keep the secret share as the original private key,
enabling deriving FROST nonces consistently regardless of the MuSig context.

* Get coordinator tests to pass

* Update spec to the new DKG

* Get clippy to pass across the repo

* cargo machete

* Add an extra sleep to ensure expected ordering of `Participation`s

* Update orchestration

* Remove bad panic in coordinator

It expected ConfirmationShare to be n-of-n, not t-of-n.

* Improve documentation on  functions

* Update TX size limit

We now no longer have to support the ridiculous case of having 49 DKG
participations within a 101-of-150 DKG. It does remain quite high due to
needing to _sign_ so many times. It'd may be optimal for parties with multiple
key shares to independently send their preprocesses/shares (despite the
overhead that'll cause with signatures and the transaction structure).

* Correct error in the Processor spec document

* Update a few comments in the validator-sets pallet

* Send/Recv Participation one at a time

Sending all, then attempting to receive all in an expected order, wasn't working
even with notable delays between sending messages. This points to the mempool
not working as expected...

* Correct ThresholdKeys serialization in modular-frost test

* Updating existing TX size limit test for the new DKG parameters

* Increase time allowed for the DKG on the GH CI

* Correct construction of signature_participants in serai-client tests

Fault identified by akil.

* Further contextualize DkgConfirmer by ValidatorSet

Caught by a safety check we wouldn't reuse preprocesses across messages. That
raises the question of we were prior reusing preprocesses (reusing keys)?
Except that'd have caused a variety of signing failures (suggesting we had some
staggered timing avoiding it in practice but yes, this was possible in theory).

* Add necessary calls to set_embedded_elliptic_curve_key in coordinator set rotation tests

* Correct shimmed setting of a secq256k1 key

* cargo fmt

* Don't use `[0; 32]` for the embedded keys in the coordinator rotation test

The key_gen function expects the random values already decided.

* Big-endian secq256k1 scalars

Also restores the prior, safer, Encryption::register function.

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

@@ -83,6 +83,12 @@ pub mod pallet {
     type ShouldEndSession: ShouldEndSession<BlockNumberFor<Self>>;
   }
 
+  #[derive(Clone, PartialEq, Eq, Debug, Encode, Decode, serde::Serialize, serde::Deserialize)]
+  pub struct AllEmbeddedEllipticCurveKeysAtGenesis {
+    pub embedwards25519: BoundedVec<u8, ConstU32<{ MAX_KEY_LEN }>>,
+    pub secq256k1: BoundedVec<u8, ConstU32<{ MAX_KEY_LEN }>>,
+  }
+
   #[pallet::genesis_config]
   #[derive(Clone, PartialEq, Eq, Debug, Encode, Decode)]
   pub struct GenesisConfig<T: Config> {
@@ -92,7 +98,7 @@ pub mod pallet {
     /// This stake cannot be withdrawn however as there's no actual stake behind it.
     pub networks: Vec<(NetworkId, Amount)>,
     /// List of participants to place in the initial validator sets.
-    pub participants: Vec<T::AccountId>,
+    pub participants: Vec<(T::AccountId, AllEmbeddedEllipticCurveKeysAtGenesis)>,
   }
 
   impl<T: Config> Default for GenesisConfig<T> {
@@ -191,6 +197,18 @@ pub mod pallet {
     }
   }
 
+  /// A key on an embedded elliptic curve.
+  #[pallet::storage]
+  pub type EmbeddedEllipticCurveKeys<T: Config> = StorageDoubleMap<
+    _,
+    Blake2_128Concat,
+    Public,
+    Identity,
+    EmbeddedEllipticCurve,
+    BoundedVec<u8, ConstU32<{ MAX_KEY_LEN }>>,
+    OptionQuery,
+  >;
+
   /// The total stake allocated to this network by the active set of validators.
   #[pallet::storage]
   #[pallet::getter(fn total_allocated_stake)]
@@ -426,6 +444,14 @@ pub mod pallet {
   pub enum Error<T> {
     /// Validator Set doesn't exist.
     NonExistentValidatorSet,
+    /// An invalid embedded elliptic curve key was specified.
+    ///
+    /// This error not being raised does not mean the key was valid. Solely that it wasn't detected
+    /// by this pallet as invalid.
+    InvalidEmbeddedEllipticCurveKey,
+    /// Trying to perform an operation requiring an embedded elliptic curve key, without an
+    /// embedded elliptic curve key.
+    MissingEmbeddedEllipticCurveKey,
     /// Not enough allocation to obtain a key share in the set.
     InsufficientAllocation,
     /// Trying to deallocate more than allocated.
@@ -469,10 +495,20 @@ pub mod pallet {
     fn build(&self) {
       for (id, stake) in self.networks.clone() {
         AllocationPerKeyShare::<T>::set(id, Some(stake));
-        for participant in self.participants.clone() {
-          if Pallet::<T>::set_allocation(id, participant, stake) {
+        for participant in &self.participants {
+          if Pallet::<T>::set_allocation(id, participant.0, stake) {
             panic!("participants contained duplicates");
           }
+          EmbeddedEllipticCurveKeys::<T>::set(
+            participant.0,
+            EmbeddedEllipticCurve::Embedwards25519,
+            Some(participant.1.embedwards25519.clone()),
+          );
+          EmbeddedEllipticCurveKeys::<T>::set(
+            participant.0,
+            EmbeddedEllipticCurve::Secq256k1,
+            Some(participant.1.secq256k1.clone()),
+          );
         }
         Pallet::<T>::new_set(id);
       }
@@ -941,14 +977,15 @@ 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();
@@ -963,15 +1000,6 @@ 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(())
@@ -1004,8 +1032,42 @@ pub mod pallet {
 
     #[pallet::call_index(2)]
     #[pallet::weight(0)] // TODO
+    pub fn set_embedded_elliptic_curve_key(
+      origin: OriginFor<T>,
+      embedded_elliptic_curve: EmbeddedEllipticCurve,
+      key: BoundedVec<u8, ConstU32<{ MAX_KEY_LEN }>>,
+    ) -> DispatchResult {
+      let validator = ensure_signed(origin)?;
+
+      // We don't have the curve formulas, nor the BigInt arithmetic, necessary here to validate
+      // these keys. Instead, we solely check the key lengths. Validators are responsible to not
+      // provide invalid keys.
+      let expected_len = match embedded_elliptic_curve {
+        EmbeddedEllipticCurve::Embedwards25519 => 32,
+        EmbeddedEllipticCurve::Secq256k1 => 33,
+      };
+      if key.len() != expected_len {
+        Err(Error::<T>::InvalidEmbeddedEllipticCurveKey)?;
+      }
+
+      // This does allow overwriting an existing key which... is unlikely to be done?
+      // Yet it isn't an issue as we'll fix to the key as of any set's declaration (uncaring to if
+      // it's distinct at the latest block)
+      EmbeddedEllipticCurveKeys::<T>::set(validator, embedded_elliptic_curve, Some(key));
+      Ok(())
+    }
+
+    #[pallet::call_index(3)]
+    #[pallet::weight(0)] // TODO
     pub fn allocate(origin: OriginFor<T>, network: NetworkId, amount: Amount) -> DispatchResult {
       let validator = ensure_signed(origin)?;
+      // If this network utilizes embedded elliptic curve(s), require the validator to have set the
+      // appropriate key(s)
+      for embedded_elliptic_curve in network.embedded_elliptic_curves() {
+        if !EmbeddedEllipticCurveKeys::<T>::contains_key(validator, *embedded_elliptic_curve) {
+          Err(Error::<T>::MissingEmbeddedEllipticCurveKey)?;
+        }
+      }
       Coins::<T>::transfer_internal(
         validator,
         Self::account(),
@@ -1014,7 +1076,7 @@ pub mod pallet {
       Self::increase_allocation(network, validator, amount, false)
     }
 
-    #[pallet::call_index(3)]
+    #[pallet::call_index(4)]
     #[pallet::weight(0)] // TODO
     pub fn deallocate(origin: OriginFor<T>, network: NetworkId, amount: Amount) -> DispatchResult {
       let account = ensure_signed(origin)?;
@@ -1031,7 +1093,7 @@ pub mod pallet {
       Ok(())
     }
 
-    #[pallet::call_index(4)]
+    #[pallet::call_index(5)]
     #[pallet::weight((0, DispatchClass::Operational))] // TODO
     pub fn claim_deallocation(
       origin: OriginFor<T>,
@@ -1059,7 +1121,7 @@ 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
@@ -1083,30 +1145,24 @@ 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;
             }
 
@@ -1124,9 +1180,7 @@ 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)?;
           }
 
@@ -1159,9 +1213,10 @@ pub mod pallet {
             .propagate(true)
             .build()
         }
-        Call::allocate { .. } | Call::deallocate { .. } | Call::claim_deallocation { .. } => {
-          Err(InvalidTransaction::Call)?
-        }
+        Call::set_embedded_elliptic_curve_key { .. } |
+        Call::allocate { .. } |
+        Call::deallocate { .. } |
+        Call::claim_deallocation { .. } => Err(InvalidTransaction::Call)?,
         Call::__Ignore(_, _) => unreachable!(),
       }
     }