fix: extend slashing of bad attestations

Author: alexghr

yarn-project/aztec-node/src/aztec-node/server.ts

@@ -753,7 +753,10 @@ export class AztecNodeService implements AztecNode, AztecNodeAdmin, AztecNodeDeb
           watchers.push(dataWithholdingWatcher);
         }
 
-        if (config.slashBroadcastedInvalidCheckpointProposalPenalty > 0n) {
+        if (
+          config.slashBroadcastedInvalidCheckpointProposalPenalty > 0n ||
+          config.slashAttestInvalidCheckpointProposalPenalty > 0n
+        ) {
           broadcastedInvalidCheckpointProposalWatcher = new BroadcastedInvalidCheckpointProposalWatcher(
             p2pClient,
             archiver,

yarn-project/slasher/README.md

@@ -123,8 +123,8 @@ List of all slashable offenses in the system:
 **Time Unit**: Slot-based offense.
 
 ### ATTESTED_TO_INVALID_CHECKPOINT_PROPOSAL
-**Description**: A committee member attested to a checkpoint proposal in a slot where this node detected a slashable invalid block proposal.
-**Detection**: ValidatorClient marks slots with invalid block proposals detected via reexecution and slashes checkpoint attesters seen for that slot. If proposal equivocation is later detected for the slot, pending bad-attestation offenses are cleared.
+**Description**: A committee member attested to a checkpoint proposal in a slot where this node detected a slashable invalid block or checkpoint proposal.
+**Detection**: ValidatorClient marks slots with invalid block proposals detected via reexecution and invalid checkpoint proposals detected via deterministic validation, then slashes checkpoint attesters seen for that slot. BroadcastedInvalidCheckpointProposalWatcher also scans retained A-520 checkpoint evidence and retained attestations for the same slot. If proposal equivocation is later detected for the slot, pending bad-attestation offenses are cleared.
 **Target**: Committee members who attested in the invalid proposal slot.
 **Time Unit**: Slot-based offense.
 

yarn-project/slasher/src/watchers/broadcasted_invalid_checkpoint_proposal_watcher.test.ts

@@ -10,6 +10,7 @@ import { OffenseType } from '@aztec/stdlib/slashing';
 import {
   makeBlockHeader,
   makeBlockProposal,
+  makeCheckpointAttestation,
   makeCheckpointHeader,
   makeCheckpointProposal,
 } from '@aztec/stdlib/testing';
@@ -22,15 +23,16 @@ import { WANT_TO_SLASH_EVENT, type WantToSlashArgs } from '../watcher.js';
 import { BroadcastedInvalidCheckpointProposalWatcher } from './broadcasted_invalid_checkpoint_proposal_watcher.js';
 
 describe('BroadcastedInvalidCheckpointProposalWatcher', () => {
-  let p2pClient: MockProxy<Pick<P2PClient, 'getProposalsForSlot'>>;
+  let p2pClient: MockProxy<Pick<P2PClient, 'getCheckpointAttestationsForSlot' | 'getProposalsForSlot'>>;
   let l2BlockSource: MockProxy<Pick<L2BlockSource, 'getSyncedL2SlotNumber'>>;
   let epochCache: MockProxy<Pick<EpochCacheInterface, 'getSlotNow' | 'getL1Constants'>>;
   let config: SlasherConfig;
   let watcher: BroadcastedInvalidCheckpointProposalWatcher;
   let handler: jest.MockedFunction<(args: WantToSlashArgs[]) => void>;
 
   beforeEach(() => {
-    p2pClient = mock<Pick<P2PClient, 'getProposalsForSlot'>>();
+    p2pClient = mock<Pick<P2PClient, 'getCheckpointAttestationsForSlot' | 'getProposalsForSlot'>>();
+    p2pClient.getCheckpointAttestationsForSlot.mockResolvedValue([]);
     l2BlockSource = mock<Pick<L2BlockSource, 'getSyncedL2SlotNumber'>>();
     l2BlockSource.getSyncedL2SlotNumber.mockResolvedValue(SlotNumber(12));
     epochCache = mock<Pick<EpochCacheInterface, 'getSlotNow' | 'getL1Constants'>>();
@@ -43,6 +45,7 @@ describe('BroadcastedInvalidCheckpointProposalWatcher', () => {
     config = {
       ...DefaultSlasherConfig,
       slashBroadcastedInvalidCheckpointProposalPenalty: 11n,
+      slashAttestInvalidCheckpointProposalPenalty: 13n,
     };
     watcher = new BroadcastedInvalidCheckpointProposalWatcher(p2pClient, l2BlockSource, epochCache, config, 4);
     handler = jest.fn();
@@ -112,6 +115,154 @@ describe('BroadcastedInvalidCheckpointProposalWatcher', () => {
     ]);
   });
 
+  it('slashes attesters when retained attestations exist for a truncated checkpoint proposal slot', async () => {
+    const signer = Secp256k1Signer.random();
+    const attester = Secp256k1Signer.random();
+    const slot = SlotNumber(10);
+    const blocks = await makeBlocks(signer, slot, 4);
+    const checkpoint = await makeCheckpointCore(signer, slot, blocks[1]);
+    const attestation = makeCheckpointAttestation({
+      header: makeCheckpointHeader(1, { slotNumber: slot }),
+      attesterSigner: attester,
+    });
+    mockProposals(slot, blocks, [checkpoint]);
+    p2pClient.getCheckpointAttestationsForSlot.mockResolvedValue([attestation]);
+
+    await watcher.scanSlot(slot);
+
+    expect(handler).toHaveBeenCalledWith([
+      {
+        validator: signer.address,
+        amount: 11n,
+        offenseType: OffenseType.BROADCASTED_INVALID_CHECKPOINT_PROPOSAL,
+        epochOrSlot: 10n,
+      },
+      {
+        validator: attester.address,
+        amount: config.slashAttestInvalidCheckpointProposalPenalty,
+        offenseType: OffenseType.ATTESTED_TO_INVALID_CHECKPOINT_PROPOSAL,
+        epochOrSlot: 10n,
+      },
+    ]);
+  });
+
+  it('slashes attesters when proposer checkpoint slashing is disabled', async () => {
+    watcher.updateConfig({ slashBroadcastedInvalidCheckpointProposalPenalty: 0n });
+    const signer = Secp256k1Signer.random();
+    const attester = Secp256k1Signer.random();
+    const slot = SlotNumber(10);
+    const blocks = await makeBlocks(signer, slot, 4);
+    const checkpoint = await makeCheckpointCore(signer, slot, blocks[1]);
+    const attestation = makeCheckpointAttestation({
+      header: makeCheckpointHeader(1, { slotNumber: slot }),
+      attesterSigner: attester,
+    });
+    mockProposals(slot, blocks, [checkpoint]);
+    p2pClient.getCheckpointAttestationsForSlot.mockResolvedValue([attestation]);
+
+    await watcher.scanSlot(slot);
+
+    expect(handler).toHaveBeenCalledWith([
+      {
+        validator: attester.address,
+        amount: config.slashAttestInvalidCheckpointProposalPenalty,
+        offenseType: OffenseType.ATTESTED_TO_INVALID_CHECKPOINT_PROPOSAL,
+        epochOrSlot: 10n,
+      },
+    ]);
+  });
+
+  it('does not slash attesters when bad attestation slashing is disabled', async () => {
+    watcher.updateConfig({ slashAttestInvalidCheckpointProposalPenalty: 0n });
+    const signer = Secp256k1Signer.random();
+    const attester = Secp256k1Signer.random();
+    const slot = SlotNumber(10);
+    const blocks = await makeBlocks(signer, slot, 4);
+    const checkpoint = await makeCheckpointCore(signer, slot, blocks[1]);
+    const attestation = makeCheckpointAttestation({
+      header: makeCheckpointHeader(1, { slotNumber: slot }),
+      attesterSigner: attester,
+    });
+    mockProposals(slot, blocks, [checkpoint]);
+    p2pClient.getCheckpointAttestationsForSlot.mockResolvedValue([attestation]);
+
+    await watcher.scanSlot(slot);
+
+    expect(handler).toHaveBeenCalledWith([
+      {
+        validator: signer.address,
+        amount: 11n,
+        offenseType: OffenseType.BROADCASTED_INVALID_CHECKPOINT_PROPOSAL,
+        epochOrSlot: 10n,
+      },
+    ]);
+  });
+
+  it('does not emit duplicate bad attestation offenses on repeated scans', async () => {
+    watcher.updateConfig({ slashBroadcastedInvalidCheckpointProposalPenalty: 0n });
+    const signer = Secp256k1Signer.random();
+    const attester = Secp256k1Signer.random();
+    const slot = SlotNumber(10);
+    const blocks = await makeBlocks(signer, slot, 4);
+    const checkpoint = await makeCheckpointCore(signer, slot, blocks[1]);
+    const attestation = makeCheckpointAttestation({
+      header: makeCheckpointHeader(1, { slotNumber: slot }),
+      attesterSigner: attester,
+    });
+    mockProposals(slot, blocks, [checkpoint]);
+    p2pClient.getCheckpointAttestationsForSlot.mockResolvedValue([attestation]);
+
+    await watcher.scanSlot(slot);
+    await watcher.scanSlot(slot);
+
+    expect(handler).toHaveBeenCalledTimes(1);
+  });
+
+  it('does not emit bad attestation offenses for equivocated checkpoint proposal slots', async () => {
+    watcher.updateConfig({ slashBroadcastedInvalidCheckpointProposalPenalty: 0n });
+    const signer = Secp256k1Signer.random();
+    const attester = Secp256k1Signer.random();
+    const slot = SlotNumber(10);
+    const blocks = await makeBlocks(signer, slot, 4);
+    const truncatedCheckpoint = await makeCheckpointCore(signer, slot, blocks[1]);
+    const otherCheckpoint = await makeCheckpointCore(signer, slot, blocks[3]);
+    const attestation = makeCheckpointAttestation({
+      header: makeCheckpointHeader(1, { slotNumber: slot }),
+      attesterSigner: attester,
+    });
+    mockProposals(slot, blocks, [truncatedCheckpoint, otherCheckpoint]);
+    p2pClient.getCheckpointAttestationsForSlot.mockResolvedValue([attestation]);
+
+    await watcher.scanSlot(slot);
+
+    expect(handler).not.toHaveBeenCalled();
+  });
+
+  it('does not emit bad attestation offenses for equivocated block proposal slots', async () => {
+    watcher.updateConfig({ slashBroadcastedInvalidCheckpointProposalPenalty: 0n });
+    const signer = Secp256k1Signer.random();
+    const attester = Secp256k1Signer.random();
+    const slot = SlotNumber(10);
+    const blocks = await makeBlocks(signer, slot, 4);
+    const equivocatedBlock = await makeBlockProposal({
+      signer,
+      blockHeader: makeBlockHeader(99, { slotNumber: slot }),
+      archiveRoot: Fr.random(),
+      indexWithinCheckpoint: IndexWithinCheckpoint(2),
+    });
+    const checkpoint = await makeCheckpointCore(signer, slot, blocks[1]);
+    const attestation = makeCheckpointAttestation({
+      header: makeCheckpointHeader(1, { slotNumber: slot }),
+      attesterSigner: attester,
+    });
+    mockProposals(slot, [...blocks, equivocatedBlock], [checkpoint]);
+    p2pClient.getCheckpointAttestationsForSlot.mockResolvedValue([attestation]);
+
+    await watcher.scanSlot(slot);
+
+    expect(handler).not.toHaveBeenCalled();
+  });
+
   it('slashes when a higher-index proposal arrives after an earlier non-slashing scan', async () => {
     const signer = Secp256k1Signer.random();
     const slot = SlotNumber(10);

yarn-project/slasher/src/watchers/broadcasted_invalid_checkpoint_proposal_watcher.ts

@@ -16,25 +16,27 @@ import { WANT_TO_SLASH_EVENT, type WantToSlashArgs, type Watcher, type WatcherEm
 
 const BroadcastedInvalidCheckpointProposalWatcherConfigKeys = [
   'slashBroadcastedInvalidCheckpointProposalPenalty',
+  'slashAttestInvalidCheckpointProposalPenalty',
 ] as const;
 
 const SCAN_SLOT_LAG = 1;
 const DEFAULT_SCAN_SLOT_LOOKBACK = 4;
+const MAX_TRACKED_OFFENSES_PER_SLOT = 2048;
 
 type BroadcastedInvalidCheckpointProposalWatcherConfig = Pick<
   SlasherConfig,
   (typeof BroadcastedInvalidCheckpointProposalWatcherConfigKeys)[number]
 >;
 
 type ProposalsForSlot = Awaited<ReturnType<P2PClient['getProposalsForSlot']>>;
-type P2PProposalsForSlotSource = Pick<P2PClient, 'getProposalsForSlot'>;
+type P2PProposalsForSlotSource = Pick<P2PClient, 'getCheckpointAttestationsForSlot' | 'getProposalsForSlot'>;
 
 type SignedBlockProposal = {
   proposal: BlockProposal;
   signer: EthAddress;
 };
 
-/** Detects truncated-checkpoint proposal offenses from retained signed P2P proposals. */
+/** Detects A-520 truncated-checkpoint proposal offenses and associated bad attestations from retained P2P evidence. */
 export class BroadcastedInvalidCheckpointProposalWatcher
   extends (EventEmitter as new () => WatcherEmitter)
   implements Watcher
@@ -58,10 +60,7 @@ export class BroadcastedInvalidCheckpointProposalWatcher
     this.config = pick(config, ...BroadcastedInvalidCheckpointProposalWatcherConfigKeys);
     this.scanSlotLookback = Math.max(1, scanSlotLookback);
 
-    // Bound emitted offenses to the number of slots we rescan. This watcher currently tracks one offense type,
-    // and at most one offense of that type can be emitted per slot.
-    const offenseTypes = 1;
-    this.emittedOffenses = FifoSet.withLimit<string>(offenseTypes * this.scanSlotLookback);
+    this.emittedOffenses = FifoSet.withLimit<string>(MAX_TRACKED_OFFENSES_PER_SLOT * this.scanSlotLookback);
 
     const intervalMs = Math.max(1000, (constants.ethereumSlotDuration * 1000) / 4);
     this.runningPromise = new RunningPromise(() => this.scan(), this.log, intervalMs);
@@ -89,7 +88,10 @@ export class BroadcastedInvalidCheckpointProposalWatcher
    * `currentSlot` at the archiver's last synced L2 slot.
    */
   public async scan(): Promise<void> {
-    if (this.config.slashBroadcastedInvalidCheckpointProposalPenalty <= 0n) {
+    if (
+      this.config.slashBroadcastedInvalidCheckpointProposalPenalty <= 0n &&
+      this.config.slashAttestInvalidCheckpointProposalPenalty <= 0n
+    ) {
       return;
     }
 
@@ -111,12 +113,17 @@ export class BroadcastedInvalidCheckpointProposalWatcher
 
   /** Scans a single slot. Public for tests. */
   public async scanSlot(slot: SlotNumber): Promise<void> {
-    if (this.config.slashBroadcastedInvalidCheckpointProposalPenalty <= 0n) {
+    if (
+      this.config.slashBroadcastedInvalidCheckpointProposalPenalty <= 0n &&
+      this.config.slashAttestInvalidCheckpointProposalPenalty <= 0n
+    ) {
       return;
     }
 
     const proposals = await this.p2pClient.getProposalsForSlot(slot);
-    const slashArgs = this.getSlashArgsForProposals(slot, proposals).filter(args => this.markAsNewOffense(args));
+    const slashArgs = (await this.getSlashArgsForProposals(slot, proposals)).filter(args =>
+      this.markAsNewOffense(args),
+    );
     if (slashArgs.length === 0) {
       return;
     }
@@ -132,15 +139,79 @@ export class BroadcastedInvalidCheckpointProposalWatcher
     this.emit(WANT_TO_SLASH_EVENT, slashArgs);
   }
 
-  private getSlashArgsForProposals(slot: SlotNumber, proposals: ProposalsForSlot): WantToSlashArgs[] {
+  private async getSlashArgsForProposals(slot: SlotNumber, proposals: ProposalsForSlot): Promise<WantToSlashArgs[]> {
     const offenders = this.findOffenders(proposals.blockProposals, proposals.checkpointProposals);
-    // we expect one proposer per slot today.
-    return [...offenders.values()].map(validator => ({
-      validator,
-      amount: this.config.slashBroadcastedInvalidCheckpointProposalPenalty,
-      offenseType: OffenseType.BROADCASTED_INVALID_CHECKPOINT_PROPOSAL,
-      epochOrSlot: BigInt(slot),
-    }));
+    if (offenders.size === 0) {
+      return [];
+    }
+
+    const proposerArgs =
+      this.config.slashBroadcastedInvalidCheckpointProposalPenalty > 0n
+        ? [...offenders.values()].map(validator => ({
+            validator,
+            amount: this.config.slashBroadcastedInvalidCheckpointProposalPenalty,
+            offenseType: OffenseType.BROADCASTED_INVALID_CHECKPOINT_PROPOSAL,
+            epochOrSlot: BigInt(slot),
+          }))
+        : [];
+
+    return [...proposerArgs, ...(await this.getBadAttestationSlashArgsForProposals(slot, proposals))];
+  }
+
+  private async getBadAttestationSlashArgsForProposals(
+    slot: SlotNumber,
+    proposals: ProposalsForSlot,
+  ): Promise<WantToSlashArgs[]> {
+    if (this.config.slashAttestInvalidCheckpointProposalPenalty <= 0n || this.hasProposalEquivocation(proposals)) {
+      return [];
+    }
+
+    let attestations: Awaited<ReturnType<P2PClient['getCheckpointAttestationsForSlot']>>;
+    try {
+      attestations = await this.p2pClient.getCheckpointAttestationsForSlot(slot);
+    } catch (err) {
+      this.log.warn(`Failed to fetch checkpoint attestations for invalid checkpoint proposal slot`, {
+        slot,
+        err,
+      });
+      return [];
+    }
+
+    const args: WantToSlashArgs[] = [];
+    for (const attestation of attestations) {
+      const attester = attestation.getSender();
+      if (!attester) {
+        continue;
+      }
+
+      args.push({
+        validator: attester,
+        amount: this.config.slashAttestInvalidCheckpointProposalPenalty,
+        offenseType: OffenseType.ATTESTED_TO_INVALID_CHECKPOINT_PROPOSAL,
+        epochOrSlot: BigInt(slot),
+      });
+    }
+    return args;
+  }
+
+  private hasProposalEquivocation(proposals: ProposalsForSlot): boolean {
+    const checkpointProposalHashes = new Set(proposals.checkpointProposals.map(proposal => proposal.getPayloadHash()));
+    if (checkpointProposalHashes.size > 1) {
+      return true;
+    }
+
+    const blockProposalHashesByPosition = new Map<string, string>();
+    for (const proposal of proposals.blockProposals) {
+      const positionKey = `${proposal.slotNumber}:${proposal.indexWithinCheckpoint}`;
+      const payloadHash = proposal.getPayloadHash();
+      const previousPayloadHash = blockProposalHashesByPosition.get(positionKey);
+      if (previousPayloadHash !== undefined && previousPayloadHash !== payloadHash) {
+        return true;
+      }
+      blockProposalHashesByPosition.set(positionKey, payloadHash);
+    }
+
+    return false;
   }
 
   private findOffenders(blockProposals: BlockProposal[], checkpointProposals: CheckpointProposalCore[]) {

yarn-project/stdlib/src/slashing/types.ts

@@ -22,7 +22,7 @@ export enum OffenseType {
   DUPLICATE_PROPOSAL = 8,
   /** A validator signed attestations for different proposals at the same slot (equivocation) */
   DUPLICATE_ATTESTATION = 9,
-  /** A committee member attested to a checkpoint proposal in a slot with an invalid block proposal */
+  /** A committee member attested to a checkpoint proposal in a slot with an invalid block or checkpoint proposal */
   ATTESTED_TO_INVALID_CHECKPOINT_PROPOSAL = 10,
   /** A proposer broadcast an invalid checkpoint proposal, detected by retained evidence or deterministic recomputation */
   BROADCASTED_INVALID_CHECKPOINT_PROPOSAL = 11,