Wormhole Core Bridge & Watcher for Canton

This directory contains the Wormhole core bridge for the Canton Network (implemented in Daml) and documents the guardian-node watcher that observes it (implemented in Go under node/pkg/watchers/canton with a Ledger-API client under node/pkg/cantonclient).

Target deployment: the public Canton Network mainnet — Canton 3.5.x protocol, Daml SDK 3.5.1 (Daml-LF 2.3, Protocol Version 35). Two consequences shape the design: Ledger API v2, and contract keys too weak to build on (non-unique, resolved against the submitter's read view, negative lookups fail open) — the package uses no contract keys: contracts are addressed by contract-id, resolved off-ledger (§4.7); identity uniqueness is registry-enforced and address integrity is cryptographic (see §1, §4).

The goal is parity with the canonical EVM core bridge (ethereum/contracts/Implementation.sol, Messages.sol, Governance.sol) and conformance with the Wormhole whitepapers:

Status: initial implementation. The Daml packages compile and tests pass on Daml SDK 3.5.1, including on-chain VAA verification validated against a real guardian-signed VAA and the cross-language address derivation pinned by a shared test vector. The remaining mainnet-gating item — the exact Ledger-API protobuf surface — plus the deployment/observer topology are tracked in Open Questions & Validation Items.

1. Background: how Canton differs from EVM

Wormhole's core bridge has two responsibilities on every chain:

Publish messages — an on-chain caller emits a message; the guardians observe it, reach quorum, and produce a signed VAA.
Verify messages (VAAs) on-chain — needed so the chain can act on governance VAAs (guardian-set upgrades, fees, upgrades) and so higher-level protocols (token bridge, etc.) can verify inbound VAAs.

Canton is structurally unlike EVM/Solana/Sui, and those differences drive the design:

Concept	EVM	Canton
Smart-contract model	Solidity contract with mutable storage	Daml templates; state is the set of active contracts (UTXO-like). State is changed by archiving a contract and creating its successor.
Calling a method	`CALL` to an address	Exercising a choice on a contract
Identity / "address"	20-byte account/contract address	Party ID (a string `hint::fingerprint`) and contract IDs
Event log	`LOG`/`event` topics	Ledger-API events (`CreatedEvent`, `ExercisedEvent`) in the transaction stream
Block / height	block number	participant offset (monotone `int64`) into the update stream
Finality	probabilistic (reorgs) → consistency levels	deterministic: once a transaction is committed by the sequencer/mediator it is final. No reorgs.
Node API the watcher uses	JSON-RPC / `eth_getLogs`	Ledger API v2 (gRPC), `UpdateService` streaming
Crypto available on-chain	`ecrecover`, `keccak256` precompiles	Daml `keccak256` and `secp256k1` built-ins (see §5)

The most consequential differences:

No msg.sender. A Daml choice knows its acting parties, but Wormhole needs a stable 32-byte emitter address with a per-emitter monotonically increasing sequence. We solve this with an Emitter registration contract (§4.2), analogous to Sui's EmitterCap. The emitting party (owner) co-signs the Emitter and is part of the address derivation, so it is the faithful Canton analog of msg.sender: only that party's key can emit under its address (§4.2, §10).
No ecrecover. Daml's secp256k1 builtin verifies a signature against a public key; it does not recover the signer from the signature like Ethereum does. Guardian-set state on Canton therefore stores guardian public keys (not just their 20-byte addresses), bound to the canonical addresses from the governance VAA (§5).
No global mutable singletons; no contract keys. The "core bridge contract" is modeled as a single long-lived CoreState contract, archived and recreated on every governance transition. Contract keys exist on Canton 3.5 (Daml-LF 2.3) but are not unique — multiple active contracts may share a key (docs) — and lookups resolve against the submission's readers, with negative results failing open (§4.6). They can carry neither uniqueness nor authenticity, so this package uses none: contracts are addressed by contract-id, resolved from a stakeholder's own ACS or via the disclosure service (§4.7), and authenticated by their payloads (signatories cannot be forged). The CoreState is co-signed by the operator and a guardianGovernance party (a k-of-n threshold party), so the operator cannot forge the guardian set (§4.1); per-emitter uniqueness is a registry that allocates ids plus an owner-bound, cryptographic address (§4.2).

2. Architecture overview

flowchart TD
    subgraph canton["Canton participant node — Daml: Wormhole.Core package"]
        direction TB
        integrator(["integrator party"])
        core["CoreState<br/>(operator-issued singleton)<br/>archives &amp; recreates on each transition"]
        gov["governance choices:<br/>GuardianSetUpgrade · SetMessageFee<br/>TransferFees · ContractUpgrade"]
        evt(["ExercisedEvent(PublishMessage)<br/>result = WormholeMessage{seq, nonce, payload, …}"])
        integrator -- "exercise PublishMessage" --> core
        gov -- "SubmitGovernanceVAA" --> core
        core -- emits --> evt
    end

    subgraph gd["guardiand"]
        direction TB
        client["node/pkg/cantonclient (gRPC client)<br/>• GetLedgerEnd → readiness / height<br/>• GetUpdates (stream) → WormholeMessage events<br/>• GetUpdateByOffset → reobservation"]
        watcher["node/pkg/watchers/canton (Watcher)<br/>decode event → common.MessagePublication → msgC"]
        client --> watcher
    end

    evt -- "Ledger API v2 (gRPC, UpdateService stream)" --> client
    watcher --> proc["guardian processor → quorum → signed VAA"]

The watcher is read-only: it never submits to Canton. It observes the PublishMessage choice's result event, maps it to a common.MessagePublication, and hands it to the processor exactly like every other watcher.

3. The VAA and the digest (unchanged across chains)

Canton uses the standard VAA v1 body and digest. Quoting 0001 and matching Messages.sol:

body = timestamp(4) ‖ nonce(4) ‖ emitterChain(2) ‖ emitterAddress(32)
       ‖ sequence(8) ‖ consistencyLevel(1) ‖ payload(var)

digest = keccak256( keccak256( body ) )          // double keccak, Ethereum-style

Guardians sign digest with secp256k1 (Ethereum ECDSA, 65-byte r‖s‖v). Replay protection records digest (the double keccak — EVM's vm.hash), both for governance (consumedGovernance, §4.4) and for integrator VAAs (the ReplayNode trie, §4.6). The on-chain Daml verifier reconstructs and re-hashes the body and checks signatures against the stored guardian set (§5).

ChainID for Canton is 72 (ChainIDCanton), the next free mainnet ID after Arc (71). It is registered in sdk/vaa/structs.go.

4. On-chain design (Daml)

Daml package name: wormhole-core (the core package). Module layout under core/daml/:

Module	Responsibility
`Wormhole.Core.Bytes`	byte/hex helpers, big-endian integer (de)serialization
`Wormhole.Core.VAA`	VAA struct, parser, digest, signature/quorum verification
`Wormhole.Core.GuardianSet`	guardian-set representation and expiry
`Wormhole.Core.State`	the `CoreState` singleton + `EmitterRegistry` and `Emitter`
`Wormhole.Core.Governance`	governance packet parsing and the governance choices
`Wormhole.Core.Setup`	initialization (`setup`)

4.1 `CoreState` — the singleton

template CoreState
  with
    operator           : Party          -- advances the singleton; the "deployer"
    guardianGovernance : Party          -- guardians' governance anchor (threshold party)
    guardianObserver   : Party          -- read-only guardian observer (stakeholder, never signs)
    chainId            : Int            -- 72
    governanceChainId  : Int            -- 1 (Solana)
    governanceContract : Bytes32        -- 0x..0004 (the governance emitter)
    guardianSetIndex   : Int            -- current set index
    guardianSets       : Map Int GuardianSet   -- index -> set (with expiry)
    messageFee         : Int            -- fee required to publish (native units)
    consumedGovernance : Set Bytes32    -- governance-only replay protection (§4.6)
  where
    signatory operator, guardianGovernance
    observer guardianObserver          -- read-only; sees governance transitions

Read-only guardian observer. guardianObserver is a template observer (hence a stakeholder/informee, never a signatory or controller) on the attestation surface — CoreState here, Emitter in §4.2. The ledger-model rule that makes this sufficient: informees of a consuming exercise include the contract's stakeholders. SubmitGovernanceVAA and PublishMessage are both consuming, so the observer sees every governance transition and the full message surface; nonconsuming ParseAndVerifyVAA (§4.3) does not reach observers, which is fine — it is a pure read. Adding an observer needs no authority and changes nothing about who can create/exercise these contracts, so guardians watch what they attest without entering Canton's confirmation path (§10). Scope is the attestation surface only — never holdings, balances, or transfer legs.

Every state-mutating choice is controller-checked (controller operator), archives the current CoreState, and creates the next one with updated fields. This is the Daml idiom for mutable state and gives us deterministic, replay-protected transitions.

Singleton co-signed by a governance party; authenticity is in the payload. The CoreState is co-signed by the operator and a guardianGovernance party — in production a decentralized-namespace external party under a k-of-n threshold of guardian keys (the Canton Network DSO construction), rotated at the topology layer without touching this template (the party id, and thus every consumer's trust anchor, is stable across rotation). Two things follow:

The operator cannot forge the guardian set. Because guardianGovernance is a signatory, a compromised operator cannot create a CoreState bearing the real governance party, so any CoreState whose guardianGovernance field is the known anchor is authentic by construction, however its cid was obtained — consumers authenticate the payload, never the resolution path (§4.7). An operator puppet could create a CoreState under a different governance party — but its payload names the wrong parties and no consumer trusts it.
Governance stays low-friction. guardianGovernance actively signs only at genesis; each SubmitGovernanceVAA inherits its authority from the archived contract (as the Emitter owner does through PublishMessage), so the operator submits governance alone. "Exactly one live CoreState" is still behavioral, but the set's contents are now anchored.

Per-emitter sequence numbers live in each Emitter (§4.2), not CoreState: a choice can only be exercised by a stakeholder, and the emitter owner is not a stakeholder of the operator-owned CoreState. Keeping the sequence in the Emitter lets the owner publish — and advance its own sequence — without the operator's authority, preserving EVM's permissionless publishMessage. CoreState holds only shared config and governance state.

Why an operator party? Canton requires every contract to have a signatory. The operator is a designated, well-known party (configured at deploy time) that owns the singleton. It has no special authority over message contents or governance outcomes — governance is gated entirely by VAA verification (§4.4). Its role is mechanical: it is the party that the daml transaction is submitted as in order to advance the singleton. This mirrors how non-EVM chains (e.g. Near) have an account that "owns" the bridge object without being able to forge messages.

4.2 Message publishing

Mirrors publishMessage(nonce, payload, consistencyLevel) from Implementation.sol:15 and whitepaper 0004.

An integrator first registers an emitter — directly, with no operator involvement. The operator runs an EmitterRegistry (created at setup); the requester exercises RegisterEmitter on it, holding only the registry's disclosure (§4.7). The flexible controller brings the requester's signature; the operator's co-signature on the created Emitter is inherited from the registry's signatory — the same authority-inheritance that powers VerifyAndConsumeVAA. Registration is permissionless (EVM/Sui parity: anyone may emit); the choice is consuming, so racing registrations contend on the registry and the loser retries with the fresh cid:

-- One per operator; allocates monotonically increasing emitter ids.
template EmitterRegistry with
    operator         : Party
    guardianObserver : Party   -- carried (field only) to thread into new Emitters
    nextId           : Int
  where
    signatory operator
    -- guardianObserver is a FIELD only here, NOT a template observer: guardians
    -- watch the attestation surface, not id allocation (least privilege).
    -- choice RegisterEmitter : (ContractId EmitterRegistry, ContractId Emitter)
    --   with requester : Party
    --   controller requester   -- operator authority inherited; no crank

template Emitter
  with
    operator         : Party
    owner            : Party
    guardianObserver : Party   -- read-only guardian observer (stakeholder, never signs)
    emitterId        : Int      -- registry-allocated
    emitterAddress   : Bytes32  -- keccak256(tag ‖ operator ‖ owner ‖ emitterId), set at creation
    sequence         : Int      -- next sequence to assign (per-emitter)
  where
    signatory operator, owner   -- owner co-signs: the msg.sender analog
    observer guardianObserver   -- read-only; sees PublishMessage (consuming)

The guardianObserver is threaded in at registration: RegisterEmitter sets the registry's field on the created Emitter. Because PublishMessage is consuming, the observer is an informee of every publish exercise (and its WormholeMessage result) plus the sequence-bumped successor Emitter create — the full message surface — with no authority (§4.1, §10).

Emitter address derivation. The 32-byte Wormhole emitter address is

keccak256( utf8("wormhole:emitter:v1")
         ‖ uint32be(len(registrar)) ‖ utf8(registrar)
         ‖ uint32be(len(owner))     ‖ utf8(owner)
         ‖ uint64be(emitterId) )

where registrar is the operator. The 4-byte length prefixes make the preimage injective across the two variable-length party ids. It is computed on-ledger at allocation (Daml DA.Crypto.Text is stable in 3.5) and stored in emitterAddress for integrators to read, but the guardian watcher re-derives it from the WormholeMessage fields and is the sole source of truth — a corrupt on-ledger value cannot spoof it.

Impersonation is cryptographically prevented (the msg.sender guarantee). Because the owner is both a signatory of the Emitter and part of the address preimage, only a transaction carrying the owner's authority can create a contract whose address is the owner's. A compromised operator therefore cannot emit under an existing emitter's address: an operator-alone forge is rejected in guardian replay (missing the owner's signature), and a colluding duplicate under a different owner derives a different, untrusted address. This is the invariant guardians verify — "the transaction is Daml-valid under the vetted package" — with no bespoke watcher logic (see §10). Registry-allocated ids give per-owner uniqueness and let one party hold many emitters, matching Sui's multiple EmitterCaps; id-sequence discipline is operator-behavioral, but address integrity is not.

Publishing — a choice on the Emitter (controller = owner), so it needs no operator authority:

-- on Emitter
choice PublishMessage : WormholeMessage
  with
    nonce            : Int            -- uint32
    payload          : Bytes          -- <= 750 bytes (whitepaper 0004)
    consistencyLevel : Int            -- uint8; see §6
    coreStateCid     : ContractId CoreState                       -- fee read (§ Fees)
    payer            : Party          -- funds messageFee; = owner for a direct publish
    feeAllocation    : Optional (ContractId Allocation, ExtraArgs)
  controller owner, payer
  do
    -- 1. charge the current messageFee to payer through CoreState (§ Fees)
    -- 2. assert payload length <= 750
    -- 3. archive self; create the successor Emitter with sequence = sequence + 1
    -- 4. return WormholeMessage{registrar, owner, emitterId, sequence, nonce,
    --      payload, consistencyLevel} -- watcher derives the address
    pure result

The choice's exercise result is the WormholeMessage. The sequence-bumped Emitter is recreated with both signatures inherited from the consumed contract; the owner is a signatory, so the successor's cid arrives on its own ACS as the transaction's CreatedEvent, and the next publish addresses that cid directly — stakeholders never need an off-ledger resolver (§4.7). The watcher reads the result directly from the ExercisedEvent.exercise_result on the Ledger-API stream (see §7). The WormholeMessage record is the wire contract between Daml and the watcher:

data WormholeMessage = WormholeMessage with
    registrar        : Party     -- the operator; address input
    owner            : Party     -- the emitting party; address input (anti-impersonation)
    emitterId        : Int       -- registry-allocated; address input
    sequence         : Int       -- uint64
    nonce            : Int       -- uint32
    consistencyLevel : Int       -- uint8
    payload          : Bytes
  deriving (Eq, Show)

Equivalent to the EVM LogMessagePublished(sender, sequence, nonce, payload, consistencyLevel) event (Implementation.sol:12), except the sender (emitter address) is derived by the watcher from (registrar, owner, emitterId) rather than carried in the record. The VAA timestamp is not carried in the record either: per whitepaper 0001/0004 the guardian derives it from the block, so the watcher reads it from the transaction's ledger effective time (Transaction.effective_at) — see §7.1.

Sequence numbers are per-emitter, start at 0, increment by 1 — identical to EVM's _state.sequences[emitter].

Fees. Whitepaper 0004 requires a fee in the chain's native token. Fees are paid via the Canton Network Token Standard (CIP-0056, V1 — the splice-api-token-*-v1 interface DARs under canton/dars/), so the bridge works with Canton Coin or any standard token, chosen at genesis (CoreState.feeInstrument, no governance action covers it):

The payer is the submitter, so the bridge only consumes allocations, never issues wallet-facing AllocationRequests (future UX work). The payer locks funds via the token registry's AllocationFactory (its wallet/CLI plus the registry's CIP-0056 OpenAPI, which supplies the ExtraArgs choice context and registry disclosures — untrusted-for-safety, liveness-only, like our own disclosure service, §4.7), with the convention executor = sender = payer, receiver = feeRecipient.
The charging choice validates the allocation — receiver, instrument, amount (≥ fee: the entire leg amount transfers, allocations are all-or-nothing, so overpayment is deliberate padding against fee-raise races), sender, and the instrument admin's signature (views are forgeable, a signature is not) — then exercises Allocation_ExecuteTransfer in the same transaction as the publish/registration/claim. Executing consumes the allocation: one-shot by activeness, no replay bookkeeping. Fees are Ints in 10^-10 token units (exactly Decimal's last digit — every fee exactly representable).
Allocation_ExecuteTransfer needs sender ∧ receiver ∧ executor authority jointly, and the receiver is the fee recipient — so all charging routes through CoreState choices (ChargeMessageFee / ChargeFee), where the recipient's authority is inherited. PublishMessage therefore references the CoreState on every publish (EVM parity: the current messageFee is read each call; a stale cid fails closed and is re-resolved). The fee is charged to payer, which equals owner for a direct publish but is named explicitly when an app publishes on a user's behalf (NTT §10); payer co-controls the publish, so it cannot be a third party who did not authorize spending its funds. Registries charge their registrationFee/claimFee the same way, skipping the CoreState entirely at fee 0.
Custody is governance-controlled: feeRecipient is the guardianGovernance threshold party, so accrued fees move only via the k-of-n guardian ceremony — the operator never touches them (the Canton analog of "fees sit in the bridge contract"). A TransferFees VAA mints an on-ledger FeeWithdrawalAuthorization (signed by guardianGovernance) recording the amount, the VAA's 32-byte recipient, and the VAA hash — the artifact the guardians' custody policy matches when threshold-signing the outbound transfer. "Only per authorization" is enforced in gg key custody, the same trust plane as the guardian keys.
Token Standard V2 (CIP-0112) is approved but not yet on mainnet; it arrives as a parallel -v2 interface family, and Wormhole.Core.Fees.chargeFee is the single seam where support would be added.

4.3 VAA verification choice

-- on CoreState; pure verification, does not mutate state
nonconsuming choice ParseAndVerifyVAA : VerifiedVAA
  with
    verifier   : Party            -- any party; the sole controller
    encodedVAA : Bytes
    pubKeys    : [(Int, Bytes)]   -- guardianIndex -> 65-byte uncompressed pubkey
  controller verifier
  do
    vaa <- parseVAA encodedVAA
    verifyVAA self vaa pubKeys     -- §5
    pure (toVerified vaa)

pubKeys are supplied by the caller because Daml verifies against a public key, not by recovery (§5). They are untrusted hints; verification fails unless each provided key hashes to the guardian address stored in the set.

This is genuinely permissionless, not merely operator-delegated. verifier is the sole controller — operator never needs to be an active party. The choice is nonconsuming and does no create/archive at all, so nothing in its body needs operator's authority for any structural reason (contrast SubmitGovernanceVAA below, which is consuming and creates a successor CoreState genuinely needing guardianGovernance's co-signature). Any external protocol — the token bridge, NTT, anything else — can verify a VAA as itself. The one real requirement is visibility, not authorization: a non-stakeholder needs CoreState explicitly disclosed to reference it at all, via Daml's Explicit Contract Disclosure feature — a data attachment, not a signature — servable by any party with read access. In Daml Script, submitWithDisclosures is the idiom. Proven both in-memory (test/daml/Test/TestCore.daml:testParseAndVerifyVAAByExternalVerifier) and against a live sandbox/participant (node/pkg/watchers/canton/core_verify_vaa_integration_test.go): a party with no relationship to CoreState at all — not operator, not guardianGovernance — verifies a real guardian-signed VAA as itself.

Integrators that must consume a VAA (redeem exactly once) use VerifyAndConsumeVAA instead, which verifies and records consumption atomically (§4.6).

4.4 Governance

Governance follows 0002. A single SubmitGovernanceVAA choice on CoreState (controller operator) verifies the VAA and dispatches on the parsed action. Module identifier is "Core" (0x00..00436f7265, 32 bytes). A governance VAA is accepted only if (matching Governance.sol:190):

verifyVAA passes against the current guardian set;
emitterChain == governanceChainId and emitterAddress == governanceContract;
module == "Core" and action matches the choice;
chain == chainId (or 0 for chain-independent actions);
digest ∉ consumedGovernance — then it is inserted (replay protection).

Supported actions (parity with GovernanceStructs.sol):

Action	ID	Payload (after 32-byte module + 1-byte action)	Behavior
ContractUpgrade	1	`chain(2) ‖ newContract(32)`	Records intent + emits an event. On Canton, "upgrade" = a Daml package upgrade; `newContract` is interpreted as the new package-id (32 bytes). See note.
GuardianSetUpgrade	2	`chain(2) ‖ newIndex(4) ‖ len(1) ‖ keys(20·len)`	Validates `newIndex == current+1`; sets old set's `expirationTime = effectiveTime + 86400`; stores new set. Requires `pubKeys` hints to bind addresses (§5).
SetMessageFee	3	`chain(2) ‖ fee(32)`	Updates `messageFee`.
TransferFees	4	`chain(2) ‖ amount(32) ‖ recipient(32)`	Moves collected fees to `recipient`. (No-op accounting until CC payments are wired.)

RecoverChainId (EVM action 5) is EVM-specific (it repairs block.chainid after a fork) and has no analog on Canton; it is intentionally omitted.

ContractUpgrade note: EVM upgrades swap a proxy implementation. Daml has no in-place code mutation; upgrading the bridge logic means deploying a new package version and having the operator migrate the CoreState to the new package via Daml's smart-contract upgrade (data-preserving). The governance VAA records the authorized target package-id on-ledger; the operator's migration is then gated by that recorded value. This is the faithful Canton analog and is the one governance action whose mechanism differs most from EVM — see Open Questions.

4.5 Guardian-set expiry

Matches EVM (Setters.sol): when a new set is installed, the previous set's expirationTime is set to effectiveTime + 86400 (1 day). verifyVAA accepts a non-current set only while effectiveTime < expirationTime. The current set never expires.

4.6 Replay protection for integrators: a trie of consumed digests

Governance replay protection is the consumedGovernance set inside CoreState (§4.4) — fine there, because governance actions are rare and already churn the singleton. App VAAs (token bridge / NTT) must not be recorded that way: Daml values have no structural sharing across contract updates, so an ever-growing set would be reserialized into every create node (payload size, participant DB write, and network cost all linear in history), and every integrator's consume would contend on the one singleton contract.

They also must not be recorded as per-digest keyed contracts (the design this replaces): Canton LF 2.3 key lookups resolve once, on the submitting participant, against the submission's readers, and the result is a pinned input to validation. Confirming participants re-check authorization, conformance, and the activeness of every contract a transaction uses — but they do not re-run key lookups against their own stores (with non-unique keys and per-party visibility there is no canonical answer, and local re-checks would make validation nondeterministic and leak private state). A positive resolution names a cid that is consistency-checked like any input; a negative one names nothing and fails open. Replay protection is precisely a negative claim ("this digest was never consumed"), so it cannot be built on key lookups — this module uses no contract keys at all.

Instead, each consumer's consumed-digest set is a prefix trie of leaf contracts (Replay.daml). A node covers a hex prefix and stores the set of digest suffixes consumed under it:

template ReplayNode
  with
    consumer       : Party    -- integrator scope party; bears the replay risk
    operator       : Party    -- co-signs: no unilateral archive or re-create
    prefix         : Bytes    -- lowercase hex, 0..63 nibbles; "" at the root
    splitThreshold : Int      -- node capacity; children inherit it
    consumed       : Set Bytes  -- suffixes, each (64 − |prefix|) nibbles
  where
    signatory consumer, operator

A trie starts as one root (empty prefix, empty set). ConsumeDigest (consuming, controller consumer) checks the node covers the digest, rejects if the suffix is already present, and recreates the node with it inserted. When the node is at splitThreshold, the consume instead splits it: all 16 children are created (one per nibble, empty ones included), suffixes bucketed by their first nibble, which is dropped. Internal nodes are never stored. The invariant: a consumer's active nodes partition the digest space — every digest has exactly one covering node, so membership in that node is global consumption truth.

Why this is sound where keys were not. "Not consumed" became a positive statement about one named contract: fetch the covering node, check absence, consume it. Every confirming participant validates the node's activeness — a stale cid conflicts and aborts; the current covering node provably contains or excludes the digest. Soundness is submitter-independent: any submitter with a disclosure of the current covering node gets a correct check, and a wrong or stale node can only fail the transaction, never replay. Where the key design failed open (a lookup that misses waves a replay through), the trie fails closed (an archived subspace has no covering node — nothing verifies).

VerifyAndConsumeVAA (nonconsuming, on CoreState, flexible controller consumer) takes the covering node's cid, verifies the VAA (§5), binds the node to the (consumer, operator) pairing, and exercises ConsumeDigest with the digest — verify + consume + act in one transaction.

Properties:

Nobody can touch someone else's scope; your own scope is your own problem. Archival alone only bricks (fail-closed); the replay vector is node re-creation. Nodes are co-signed, so no third party can archive or re-create them (splits inherit both signatures from the archived parent — the operator is not involved per consume), and roots come only from the operator's ReplayRootRegistry — a stateless, never-churning anchor whose nonconsuming ClaimReplayRoot lends the operator's inherited signature to a consumer-submitted claim (the RegisterEmitter pattern: no crank; the operator multisig signs nothing after genesis). Claiming a root for a consumer requires that consumer's authority, so nobody can fork another app's replay scope. There is deliberately no one-root-per-consumer enforcement: maintaining a single trie is the consumer's own responsibility (its disclosure service defines which trie its consumes resolve into, and detects forks — more than one covering node — for free). This is EVM parity: nobody grants replay storage there either; every integrator owns its mapping. A consumer minting parallel roots, like a consumer whose key is stolen, only harms itself — and a stolen consumer key defeats the app more directly anyway. (If key-compromise resilience is ever wanted, the hardening is trie-identity pinning: thread the original root's cid through successors via self and pin it in the app contract — documented, not built.) Spam claims cost the spammer synchronizer traffic per transaction and the operator ~300 B of storage per worthless root; no shared contract grows, nothing bricks.
Scoping and contention. Tries are per consumer party: different apps consume the same VAA independently. Consumes racing on the same node conflict — exactly one commits (validator-checked, regardless of submitter); the loser re-resolves the covering node and retries. A blind retry of a consume that actually committed fails on membership ("digest already consumed") — a clean idempotency signal. Until the first split, all of one app's consumes serialize through its root; 16-way fan-out begins at splitThreshold consumes.
Cost. defaultSplitThreshold = 128: suffixes are ≤64-char hex (~66 B serialized), so nodes top out ~8.5 KB, the average consume rewrites ~4 KB, and the split transaction redistributes the same bytes across 16 creates (~15 KB) — all far below Canton's request caps. Total ACS bytes stay ~66 B per digest; 10 M digests ≈ 150 k nodes at depth 3–4. Larger thresholds thin the ACS but amplify every write.
Privacy. Nodes are integrator-private safety state — deliberately NOT observed by guardianObserver (§4.1): guardians never re-check target-chain consumption, and the attestation surface does not include app redemptions.

The disclosure service. Submitters locate the covering node off-ledger: a service indexes the consumer's active nodes by prefix (following the CreatedEvents that consumes and splits produce) and serves, for a digest, the covering node's cid plus its explicit disclosure — alongside the CoreState disclosure it already serves (§4.3). It is untrusted for safety: the worst it can do is serve a wrong or stale node, which fails the transaction. It is trusted for liveness only, like any RPC endpoint. §4.7 aggregates every resolution the service must provide. (Go implementation is future work; the Daml tests simulate it with a script helper, Test.TestReplay.coveringNode, which also asserts the partition invariant on every use.)

Integrating — direct and user-submitted. The executable reference is test/daml/Test/ExampleIntegrator.daml (test package only): the end user herself exercises Redeem on the app contract with two disclosures attached (CoreState + covering node) and nothing else — no read grants, no readAs, no relayer queue. The manager's authority for the consume is inherited from the app contract's signatory; its visibility is simply not needed. testIntegratorRedeem pins the inversion of the key-based design's failure mode: replay attempts by arbitrary submitters fail on activeness (stale node) or membership (fresh node) — never succeed.

4.7 Addressing without keys: the disclosure service

With contract keys gone (§1), every contract reference is a contract-id. Two distinct needs hide behind "how do I find the contract", and they have different answers:

Cid resolution — what is the current cid of X? Stakeholders get this for free: a consuming exercise delivers the successor's CreatedEvent to every stakeholder's ACS, so the operator tracks its registries and the CoreState, an emitter owner tracks its Emitter, a consumer tracks its trie — all without any off-ledger help.
Disclosure attachment — a non-stakeholder submitter must additionally attach the explicit-disclosure blob of every contract its transaction references, or its participant cannot construct the transaction at all.

The disclosure service is the single off-ledger component that provides both to the parties that need them: an index over the relevant contracts — fed by the update stream / ACS of a party that sees them — answering "current cid (+ disclosure blob) for X". The complete inventory it must serve:

Contract	Index	Needed by	Disclosure attachment?	Churn
`CoreState`	the one true instance	§4.3 verify, §4.6 consume, and EVERY publish / fee'd onboarding (§4.2)	yes — every non-stakeholder submitter (incl. all publishers)	per governance action (rare)
`ReplayNode`	(consumer, prefix covering digest)	every `VerifyAndConsumeVAA` / integrator redeem	yes for non-stakeholders (e.g. end users); the consumer itself only needs the cid	every consume under that node
`EmitterRegistry`	operator	`RegisterEmitter`	yes — the requester submits	per emitter registration; recreated on operator fee change
`ReplayRootRegistry`	operator	`ClaimReplayRoot`	yes — the consumer submits (cacheable blob)	only on operator fee change
`Emitter`	(operator, owner, emitterId)	`PublishMessage`	no — owner submits, own ACS (but see `CoreState` row)	per publish
token-registry context	the fee instrument's registry	any fee'd choice (§4.2): `ExtraArgs` + registry disclosures	yes — from the REGISTRY'S own CIP-0056 OpenAPI, not this service	registry-defined
app contracts (e.g. `ExampleIntegrator`)	app-defined	the app's own choices	app's concern (its users are observers)	app-defined

Two properties make this safe to outsource:

Untrusted for safety. A wrong or stale answer can only make the transaction fail — the trie fails closed on staleness (§4.6), and consumers authenticate every resolved contract by its payload, never by how the cid was found: CoreState by its signatory anchor fields (§4.1), ReplayNode by the (consumer, operator) binding inside VerifyAndConsumeVAA plus the app-side operator pin (see ExampleIntegrator.Redeem). The service is trusted for liveness only, like any RPC endpoint.
One reader suffices. A service reading as the operator (a stakeholder of CoreState, both registries, and — as co-signatory — every consumer's trie) can serve the whole table; integrators can equally run their own for their trie and app contracts. Reading as a party requires only that party's CanReadAs on the serving participant.

Concrete implementation (interface: (template, index) → (cid, created_event_blob) over the state-service ACS plus the update stream) is future work; the Daml tests simulate it with Test.TestReplay.coveringNode / queryDisclosure.

5. On-chain signature verification (the crux)

EVM uses ecrecover(digest, v, r, s) and compares the recovered 20-byte address to guardianSet.keys[i]. Daml's DA.Crypto.Text has no recovery builtin; the relevant functions (confirmed against the 3.x docs) are:

keccak256             : BytesHex -> BytesHex
secp256k1             : SignatureHex -> BytesHex -> PublicKeyHex -> Bool  -- SHA-256s the message first
secp256k1WithEcdsaOnly : SignatureHex -> BytesHex -> PublicKeyHex -> Bool  -- verifies the message directly

We use secp256k1WithEcdsaOnly because Ethereum signs the 32-byte keccak256(keccak256(body)) digest directly (no further hashing); plain secp256k1 would SHA-256 the digest first and never match. The design:

Bind a caller-supplied pubkey → guardian address. There is no recovery, so the verifier is given pubKeys : [(Int, Bytes)] (the signing guardians' uncompressed keys) and asserts keccak256(pubKey)[12..32] == keys[index]. Because the address is the keccak of the key, a wrong key can't pass — this re-introduces the EVM guarantee without recovery.
DER-encode for the builtin. secp256k1WithEcdsaOnly wants a DER signature and a DER (SubjectPublicKeyInfo) public key, both hex. Wormhole.Core.VAA DER-encodes the VAA's raw (r, s) (derSignature) and wraps the uncompressed point in the fixed secp256k1 SPKI prefix (derPublicKey). The 32-byte digest is passed as the message as-is.
Verify. secp256k1WithEcdsaOnly (derSignature r s) digest (derPublicKey pubKey).
Quorum — identical to EVM Messages.sol:90: required = floor(numGuardians * 2 / 3) + 1. Signatures must be in strictly ascending guardian-index order (prevents double-counting).

Making verification hint-free for integrators (recommended)

Supplying pubKeys on every call is acceptable for governance (rare, operator-submitted) but is real friction for integrators (e.g. a token bridge), whose relayers would otherwise have to look up the signing guardians' keys on every inbound message. The recommended evolution: persist the guardian public keys in the guardian set — i.e. GuardianSet stores pubKeys alongside keys, bound to the canonical addresses once at install time (the GuardianSetUpgrade / setup choices already receive pubkey hints and verify keccak256(pubKey)[12..32] == addr, so the binding is free). After that, verifyVAA reads the keys from the set and callers pass only the VAA bytes, making the integrator API equivalent to EVM's parseAndVerifyVM(bytes). This is a planned change to the current code, which still takes per-call hints.

Validation status

The whole verification path is empirically validated against a real Ethereum-style guardian signature on Daml SDK 3.5.1. testParseAndVerifyVAA and testGovernanceSetMessageFee (in TestCore.daml) feed a genuine VAA — signed by the well-known devnet guardian and produced by node/pkg/cantonclient/vectorgen_test.go — through ParseAndVerifyVAA / SubmitGovernanceVAA and both pass. That confirms:

✅ keccak256 hashes the decoded hex bytes (the double-keccak digest matched the signature), so the BytesHex semantics are as assumed;
✅ derSignature (DER r,s) and derPublicKey (SPKI) are encoded correctly;
✅ secp256k1WithEcdsaOnly verifies the 32-byte digest directly (no pre-hash), and the pubkey→address keccak binding holds.

As of Daml SDK 3.5 the DA.Crypto.Text builtins are stable (the earlier Alpha -Wno-crypto-text-is-alpha suppression is no longer needed), so the previous mainnet-readiness concern about depending on an Alpha builtin is resolved. All Daml crypto remains encapsulated in Wormhole.Core.VAA, and the same builtins now also back the on-ledger address derivation in Wormhole.Core.Bytes (toHex + keccak256).

6. Consistency / finality

Canton transactions are final once committed by the synchronizer (sequencer + mediator); there are no reorgs. Like Sui, Canton therefore has a single meaningful consistency level. The watcher treats every observed message as final and publishes immediately. The consistencyLevel byte is passed through from the WormholeMessage (integrators may set it; per 0001 "all other chains … this field will be 0"), and the watcher does not gate on it.

7. Off-chain design (the watcher)

Lives in node/pkg/watchers/canton; the gRPC client is node/pkg/cantonclient. It mirrors the structure of the Sui watcher (node/pkg/watchers/sui) and the suiclient package.

7.1 `cantonclient` (Ledger API v2, gRPC)

There is no official Go binding for the Daml Ledger API, so the com.daml.ledger.api.v2 protobuf (the State + Update service closure, from Canton 3.5.5) are vendored under node/pkg/cantonclient/proto and compiled with the repo's buf toolchain; the generated stubs are committed and CI-verified (see node/pkg/cantonclient/README.md). The client exposes a small interface (mirroring suiclient.SuiClient):

type CantonClient interface {
    // GetLedgerEnd returns the current participant offset (the "height").
    GetLedgerEnd(ctx context.Context) (int64, error)

    // SubscribeUpdates streams transactions from beginExclusive onward,
    // delivering each Wormhole message-publish event found in them.
    SubscribeUpdates(ctx context.Context, beginExclusive int64, templateID TemplateID, choiceName string, out chan<- CantonMessageEvent) (Subscription, error)

    // GetUpdateByOffset fetches a single transaction by offset (reobservation).
    GetUpdateByOffset(ctx context.Context, offset int64) (CantonTransaction, error)

    Close() error
}

Mapping to Ledger API v2 RPCs:

Need	Ledger API v2
height / readiness	`StateService.GetLedgerEnd` → `offset (int64)`
live message stream	`UpdateService.GetUpdates` (server stream); filter `Transaction.events[].exercised` by `template_id` + `choice == "PublishMessage"`
reobservation	`UpdateService.GetUpdateByOffset` (or `GetTransactionByOffset`) for the offset encoded in the reobservation request

The Wormhole message comes from the ExercisedEvent of the PublishMessage choice: exercise_result is the WormholeMessage record (§4.2), decoded from the Ledger-API Value/Record representation. The watcher derives the 32-byte emitter address from the record's registrar, owner, and emitterId fields using the canonical encoding in §4.2 (see deriveEmitterAddress in watcher.go); the encoding is pinned against the Daml side by a shared cross-language test vector.

Party filter. The GetUpdates request uses an UpdateFormat with a wildcard template filter under filters_for_any_party by default — the watcher observes PublishMessage from every emitter on the participant and needs no operator party id. For production guardians, set --cantonReadAsParty to the read-only guardianObserver party (§4.1): it is a stakeholder of the Emitter/CoreState attestation surface, so the narrowed filters_by_party stream still carries every PublishMessage, and it makes the trust boundary explicit. If the guardian participant hosts only guardianObserver the wildcard default is equivalent, so the flag is precision / defense-in-depth. The devnet sandbox is a single participant, so it keeps the wildcard default. TRANSACTION_SHAPE_LEDGER_EFFECTS is required so ExercisedEvents — which carry the choice result — are included.

7.2 `TxID` and offsets

The Ledger API has no 32-byte transaction hash. We use the participant offset (int64) as the canonical transaction identifier:

MessagePublication.TxID = the transaction's offset, big-endian, left-padded to 32 bytes (so it round-trips through the 32-byte tx_hash reobservation field).
Reobservation decodes those 32 bytes back to an int64 offset and calls GetUpdateByOffset.

The Daml update_id (a string) is carried in logs for human correlation but is not the TxID, because reobservation plumbing (gossipv1.ObservationRequest) uses raw bytes and offsets are the stable, range-queryable key.

7.3 `Run` loop (three goroutines, mirrors Sui)

flowchart TD
    run(["Run(ctx)"]) --> init["client = cantonclient.New(rpc)<br/>end = client.GetLedgerEnd(ctx)<br/>(connectivity check; set height; readiness)"]
    init --> ready["supervisor.Signal(healthy); readiness.SetReady"]
    ready --> pump["RunWithScissors: canton_data_pump<br/>SubscribeUpdates(from end) → decode → msgC"]
    ready --> height["RunWithScissors: canton_block_height<br/>every 5s: GetLedgerEnd → SetNetworkStats + readiness"]
    ready --> reobs["RunWithScissors: canton_fetch_obvs_req<br/>obsvReqC → GetUpdateByOffset → re-emit (IsReobservation=true)"]
    pump --> sel{"select: ctx.Done / errC"}
    height --> sel
    reobs --> sel

Each observed event becomes a common.MessagePublication (chainlock.go) with EmitterChain = vaa.ChainIDCanton, EmitterAddress = deriveEmitterAddress(registrar, owner, emitterId), Unreliable = false, then is sent on msgC.

7.4 Configuration

WatcherConfig (implements watchers.WatcherConfig):

type WatcherConfig struct {
    NetworkID   watchers.NetworkID
    ChainID     vaa.ChainID        // ChainIDCanton
    Rpc         string             // host:port of the Ledger API
    PackageID   string             // package-id of wormhole-core (template filter)
    ReadAsParty string             // optional; production guardians set the guardianObserver party
}

Wired into the guardian via node/pkg/node/options.go and a --cantonRPC / --cantonContract flag pair in node/cmd/guardiand, following the Sui pattern. --cantonReadAsParty populates ReadAsParty; production guardians set it to the read-only guardianObserver party (§4.1, §7.1), and devnet leaves it empty (wildcard).

8. File map

canton/
  README.md                      ← this document
  multi-package.yaml             ← multi-package project (core + test)
  Dockerfile                     ← devnet image (build DARs + run sandbox)
  core/                          ← `wormhole-core` package (templates; NO daml-script)
    daml.yaml
    daml/Wormhole/Core/Bytes.daml
    daml/Wormhole/Core/VAA.daml
    daml/Wormhole/Core/GuardianSet.daml
    daml/Wormhole/Core/State.daml
    daml/Wormhole/Core/Replay.daml
    daml/Wormhole/Core/Fees.daml ← CIP-0056 fee collection (chargeFee, §4.2)
    daml/Wormhole/Core/Governance.daml
    daml/Wormhole/Core/Setup.daml
  dars/                          ← vendored token-standard interface DARs (provenance in dars/README.md)
  test/                          ← `wormhole-core-test` package (Daml Scripts)
    daml.yaml                    ← data-dependency on core's DAR + the interface DARs
    daml/Test/TestCore.daml      ← unit tests + devnet `setup` / `integrationPublish`
    daml/Test/TestGuardianObserver.daml ← read-only guardianObserver visibility/authority tests
    daml/Test/TestReplay.daml    ← replay-trie tests + disclosure-service simulation (§4.6)
    daml/Test/MockToken.daml     ← minimal CIP-0056 mock instrument for fee tests
    daml/Test/TestFees.daml      ← fee-payment tests (§4.2)
    daml/Test/ExampleIntegrator.daml ← reference integrator + disclosure/replay e2e (§4.6)
  devnet/
    start_sandbox.sh             ← starts the Ledger API v2 sandbox
    bootstrap.sh                 ← allocates Operator + creates CoreState
    wait_for_ledger.sh

node/pkg/cantonclient/           ← Ledger API v2 gRPC client
  proto/com/daml/ledger/api/v2/  ← real vendored protos (Canton 3.5.5)
  proto/gen/                     ← generated Go stubs (buf generate)
  vectorgen_test.go              ← regenerates the signed-VAA test vector (GEN_CANTON_VECTORS=1)
node/pkg/watchers/canton/        ← the watcher (config.go, watcher.go)
  watcher_integration_test.go    ← dpm-driven end-to-end test (integration tag)
  core_verify_vaa_integration_test.go ← ParseAndVerifyVAA by a non-stakeholder external party (integration tag)
sdk/vaa/structs.go               ← ChainIDCanton = 72
devnet/canton-devnet.yaml        ← Tilt k8s manifest (sandbox + bootstrap)
Tiltfile                         ← `canton` component (opt-in)

9. Local development

This project uses the Canton Network dpm toolchain (not the legacy daml assistant). It is a multi-package project (multi-package.yaml): core (the production wormhole-core templates — no daml-script) and test (wormhole-core-test, the Daml Scripts, with a data-dependency on core's DAR). Splitting keeps daml-script and the test code out of the production DAR.

Building & testing with `dpm`

# one-time: install the dpm CLI
curl https://get.digitalasset.com/install/install.sh | sh

cd canton
dpm install 3.5.1                # fetch the pinned SDK (Daml-LF 2.3)
dpm build --all                  # builds core, then test → *.daml/dist/*.dar
cd test && dpm test --all --show-coverage   # run the Scripts + coverage

dpm test runs every Script in TestCore.daml on an in-memory ledger — no running sandbox required. The suite passes, including governance and VAA verification with a real guardian-signed VAA test vector (§5) and the owner-bound emitter address derivation pinned against the shared cross-language vector (testAddressVector). Note Daml coverage is template/choice coverage only; the pure parser / DER / governance helpers and the address encoding are additionally validated by Script assertions and the signed-VAA / address vectors, not by the coverage metric.

Watcher integration test (dpm + Go)

The watcher's real transport is covered end-to-end by a Go integration test, node/pkg/watchers/canton/watcher_integration_test.go (//go:build integration):

go test -tags integration -run TestCantonWatcherIntegration ./pkg/watchers/canton -v

It builds the DAR, boots a dpm sandbox, publishes a message via dpm script --upload-dar, then connects the real cantonclient gRPC client (real Ledger API v2 protos) and asserts the published WormholeMessage is observed and mapped to a common.MessagePublication. It is skipped unless dpm (+ a JDK) is present and is excluded from the default build. Notes learned the hard way and baked into the test/devnet scripts: Canton's sandbox binds the Ledger API on 6865 and does not take --dar/--port; and dpm script needs --upload-dar so package vetting is synchronous (a bare upload races vetting → PACKAGE_SELECTION_FAILED).

End-to-end with Tilt

Canton is wired into Tiltfile as an opt-in component (--canton), mirroring the Sui setup:

tilt up -- --canton

This brings up:

a canton pod running a Canton sandbox (Ledger API v2 on :6865) (devnet/start_sandbox.sh);
a canton-contracts bootstrap step that uploads+vets the wormhole-core DAR (dpm script --upload-dar), allocates the Operator party, and creates the CoreState with the standard devnet guardian via Test.TestCore:setup (devnet/bootstrap.sh); and
the guardian configured with --cantonRPC canton:6865 (no --cantonReadAsParty: the watcher uses a wildcard "any party" filter, §7.1).

`guardianGovernance` external-party bootstrap

devnet/setup_guardian_governance.sh + devnet/guardian_governance.canton stand up guardianGovernance as an external, decentralized-namespace party — a namespace owned by three guardian keys with a 2-of-3 threshold, the same pattern the Canton Network DSO party uses (§10, §11 item 2). Concretely, the console script:

self-signs a root NamespaceDelegation for each of the three owner keys;
creates a DecentralizedNamespaceDefinition (2-of-3 threshold) over those three owner namespaces, authorized by all three;
allocates guardianGovernance::<namespace> under it and hosts it at Confirmation permission, with the same three keys registered as its threshold transaction-signing keys (PartyToParticipant.partySigningKeys — the standalone PartyToKeyMapping was deprecated in Canton 3.4 in favor of this); and
writes an artifacts JSON (party id, decentralized-namespace id, owner fingerprints/public-key paths, threshold) that is the handoff to submitting the same topology to the CN global synchronizer later.

Every topology transaction is built unsigned (topology.transactions.generate), signed by each owner's external signer, and only then submitted (topology.transactions.load) — the participant never holds an owner's private key, matching real guardian custody (HSM/KMS/offline signer). devnet/guardian_key_tool.js is a small Ed25519 keypair/signing helper (Node's built-in crypto module only, no dependencies) that stands in for that custody system locally; production wires GG_OWNER_SIGN_CMD_1/2/3 to the real one instead (see the script's header for the full environment-variable contract).

devnet/genesis_guardian_governance.sh exercises the resulting party: it prepares a create CoreState command co-signed by an external operator party and guardianGovernance (the interactive-submission equivalent of Test.TestCore:setup's submit (actAs operator <> actAs guardianGovernance)), has owners sign the prepared transaction hash, and executes. It supports three modes — happy (2-of-3, succeeds), threshold (1-of-3, rejected), and forge (no guardianGovernance signature at all, rejected — the anti-forgery property from §10: a compromised operator cannot fabricate a CoreState bearing the real governance party).

devnet/test_guardian_governance.sh runs all of the above against a fresh dpm sandbox and asserts the full table: namespace/threshold/hosting shape, and all three genesis modes' expected outcome.

canton/devnet/test_guardian_governance.sh

Sandbox vs. CN fidelity. The sandbox has no SVs or decentralized synchronizer, so "registering with the super-validators" cannot be exercised locally. That step is theoretical here by construction, not by omission: the decentralized namespace is guardian-owned, so SVs never approve it — CN "registration" is just (a) onboarding a participant to the CN global synchronizer (one-time, SV-sponsored validator onboarding) and (b) submitting the same topology transactions this script builds to that synchronizer instead of the sandbox's, where they are sequenced and seen by all participants. The script is synchronizer-target-parameterized (GG_SYNCHRONIZER_ALIAS, GG_CANTON_CONSOLE_CONFIG) for exactly that reason, and the local run proves the namespace/party/threshold mechanics port unchanged.

Current limitation. Party hosting is single-participant only (HostingParticipant(participant.id, Confirmation) for the one console-bound participant) — the sandbox has only one participant to host on, so multi-participant Confirmation hosting (the production censorship-resistance requirement) is not exercised locally. Extending the Seq[HostingParticipant] built in guardian_governance.canton to additional participant ids is mechanical; each additional participant's consent-to-host signature follows the same transactions.sign(..., signedBy = Seq(<that participant's fingerprint>)) pattern already used for the first one.

Status: opt-in while the k8s devnet path is validated

Unlike Sui, the canton component is not enabled by --ci. The guardian builds the real client by default (no build tag) and the watcher needs no operator party id (wildcard filter), so there are no functional gates left — the main item to finish is:

Full k8s path validation. Validated locally: the Go integration test (§9) covers the watcher↔ledger path; the sandbox 0.0.0.0 bind (-C canton.participants.sandbox.ledger-api.address=0.0.0.0 → binds *:6865), the bootstrap dpm script --upload-dar flow, and the same-pod localhost wiring are all confirmed against a live dpm sandbox. What still needs a real cluster run: the canton-node image build (canton/Dockerfile, which fetches dpm and builds the DARs) and the guardian connecting to canton:6865 across the k8s Service.

Today --canton stands up the chain + contracts for Daml-side development (iterating on the templates, dpm test); the watcher↔ledger path itself is covered by the integration test in §9.

10. Trust model & deployment topology

How does a set of n guardians (k-of-n threshold) run Wormhole on Canton faithfully — see and attest only what actually happened under rules they accept — given Canton has no global VM that every node re-executes? Two requirements, met by two mechanisms:

"The code is what we published." Daml code identity is content-addressed: a DAR's package-id is the hash of the compiled package, and every Ledger-API event carries it (the watcher already filters on WatcherConfig.PackageID). Publish source + a reproducible build, and each guardian's participant vets that exact package-id before its parties transact under it. A lookalike package simply does not match the filter.
"The events are real." Canton's synchronizer (sequencer + mediator) orders and tallies but never runs Daml. Execution integrity comes from the participant nodes hosting a transaction's stakeholders re-executing the choice from the vetted DAR and confirming the result; a transaction commits only if the confirmation policy over those participants is met.

Topology. Each guardian runs a participant node, and the read-only guardianObserver party (§4.1) is hosted on every guardian participant at Observation permission in the PartyToParticipant topology mapping. Being a template observer on Emitter/CoreState, it is an informee of every PublishMessage and SubmitGovernanceVAA exercise, so each guardian's participant independently receives and validates every attestation-bearing transaction, and an invalid one never appears on that participant's Ledger API — so a watcher cannot sign it. This is deliberately scoped to the attestation surface only (§4.1, §4.2): the observer is not a stakeholder of EmitterRegistry allocations, replay tries, or any holding/balance/transfer state of other packages — least privilege, in contrast to replica-hosting the operator (whose projection is its entire signatory footprint; kept as a fallback below). A single shared guardianObserver covers all guardians (one mapping listing every guardian participant), not one party per guardian.

Guardians are not given confirmation rights, by two independent properties: (1) under Canton's confirmation policy the confirming parties of a node are its signatories/actors — a plain observer party is an informee, never a confirming party; and (2) even for a confirming party, a participant hosting it at Observation permission does not submit confirmations. So guardian participant downtime never blocks a Canton transaction; it only delays that guardian's own observation (fail-safe: it stops signing). This is the point — the VAA quorum is already the attestation layer, and Wormhole's job is to refuse to attest forgeries, not to halt Canton (giving guardians confirmation duty would duplicate the quorum and turn guardian downtime into a chain-halt).

Fallback (interim, no template change): where a participant cannot yet host the dedicated party, replica-host the operator at Observation instead. It works with zero Daml change but gives a coarser scope (the operator's full projection, including registries and replay tries) and couples guardian read access to the operator party and its namespace key. Prefer the dedicated guardianObserver; use operator replica-hosting only as a migration stopgap.

Note the operator party's ACTIVE signing surface after genesis is empty: every day-to-day flow (RegisterEmitter, ClaimReplayRoot, fee charging, splits, governance transitions) reaches its signature by inheritance from contracts it signed at setup. If the operator is stood up as a k-of-n external threshold party (the §9 machinery, GG_THRESHOLD=k), the interactive-submission signing ceremony is needed for genesis only. The guardianGovernance party's post-genesis surface grew with fees (§4.2): it holds fee custody (accrued fees sit in its token holdings; withdrawing them is a threshold ceremony matched against on-ledger FeeWithdrawalAuthorizations), and — because every publish reads the fee off the CoreState — its participant is an informee of every publish, a deliberate throughput/liveness trade recorded in Open Questions.

What a compromised operator can and cannot do. It can degrade liveness (stop serving disclosures, evict observers — all fail-safe: transactions stop constructing, guardians simply stop seeing and stop signing). It cannot produce anything guardians would wrongly attest: emitting under an existing address requires that owner's signature (§4.2), so an outbound forge is either an invalid transaction (rejected in replay, never observed) or a valid contract with a different, untrusted address.

Crucially, it also cannot forge the guardian set used for inbound verification: CoreState is co-signed by the guardianGovernance threshold party (§4.1), so the operator can neither mutate the real CoreState nor fabricate one whose payload names the governance anchor consumers trust. This closes the one gap that observation-only hosting does not cover — inbound state integrity — by moving it from "trust the single operator" to "trust the k-of-n governance party." Compromising that is a threshold compromise, i.e. genuinely takeover-class, rather than a single-key bar. Residual inbound corruption (bugs in a verification path, not forged state) can still only damage Canton-local state — the same position Wormhole holds on every chain, where a compromised chain wrecks its own state but cannot forge messages other chains accept. The guardians' faithfulness invariant thus reduces to "the transaction is Daml-valid under the vetted package."

The observer-party mechanism is now implemented: a dedicated read-only guardianObserver named as a template observer on Emitter/CoreState (§4.1, §4.2). The residual operational item is namespace-key custody — which key owns the guardianObserver party (operator-ops vs a guardian-ops key), since that key controls the hosting mapping and can therefore evict guardians from observation. Eviction is fail-safe (guardians stop seeing → stop signing, the same liveness posture as a compromised operator above), but the custody choice needs a human decision; see Open Questions.

11. Open Questions & Validation Items

Ledger API v2 RPC surface. The exact message/field names of UpdateService.GetUpdates / GetUpdateByOffset / StateService.GetLedgerEnd shift slightly across Canton releases (e.g. begin_exclusive/end_inclusive, Update one-of members). The vendored proto subset targets a specific release — confirm and pin against Daml SDK 3.5.1 / Canton 3.5.x.
guardianGovernance threshold party. CoreState is co-signed by a guardianGovernance party (§4.1), so guardian-set integrity is anchored to it rather than the operator. §9's guardianGovernance external-party bootstrap stands it up as a decentralized-namespace external party governed by a 2-of-3 threshold of guardian keys (DSO-style), and its genesis co-sign ceremony is confirmed locally (2-of-3 succeeds, 1-of-3 and no-signature are rejected). Remaining before production: the CN-synchronizer submission itself (only designed/parameterized here, not exercised — no CN localnet available), the topology-level rotation flow (add/remove guardian keys without touching CoreState — the decentralized namespace's own threshold governs this once created, but rotation itself is untested), multi-participant Confirmation hosting, and confirming consumers are configured with the correct anchor party id. Note the CoreState singleton count ("exactly one") is still behavioral — confirm the genesis automation creates exactly one. (Emitter/manager address integrity is separately owner-bound and owner-co-signed, §4.2.)
Guardian observer topology. Mechanism resolved: the dedicated read-only guardianObserver party is implemented as a template observer on Emitter/CoreState (§4.1, §4.2, §10), and --cantonReadAsParty maps to it for production guardians (§7.1). This observer party is distinct from the guardianGovernance signatory party (item 2): the observer is read-only, the governance party has signatory power. Residual (needs a human decision): the production PartyToParticipant runbook (host at Observation permission; host the party before genesis, or run Canton party replication / ACS import so a late-joining participant receives prior contracts), and namespace-key custody for the party (operator-ops vs guardian-ops key, which controls the hosting mapping and thus observer eviction — fail-safe either way).
Integrator VAA verification. Implement the hint-free guardian set (persist pubkeys, §5) and confirm the guardian-set distribution mechanism for integrators (explicit disclosure vs public-observer snapshot).
Native fees. Mechanism resolved: CIP-0056 (Token Standard V1) allocations, consumed atomically inside PublishMessage / RegisterEmitter / ClaimReplayRoot, with fee custody under the guardianGovernance threshold party and TransferFees minting on-ledger withdrawal authorizations (§4.2). Residual: validate against real amulet on DevNet (the test suite uses a mock token implementing the interfaces; the real registry adds choice contexts, deadlines, locking, and featured-app rewards — the executor earns them as the amulet "provider"); the fee instrument and recipient are genesis-fixed (no governance action — decide whether that needs one before mainnet); the CoreState reference on every publish adds operator + guardianGovernance participants to the publish informee set (throughput/liveness trade to size); a TransferFees VAA test vector (vectorgen) for the withdrawal-authorization path; Token Standard V2 (CIP-0112) migration when it reaches mainnet (Wormhole.Core.Fees.chargeFee is the seam).
ContractUpgrade mechanism. Confirm the operator-driven Daml package upgrade flow and how strictly the recorded target package-id should gate it. (The package uses no contract keys, so the upgrade constraint that keys cannot be added to a deployed template does not apply.)
Governance emitter. Uses the standard governance emitter (Solana, chain 1, address 0x00..04). Confirm for the target deployment/network.

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Wormhole Core Bridge & Watcher for Canton

1. Background: how Canton differs from EVM

2. Architecture overview

3. The VAA and the digest (unchanged across chains)

4. On-chain design (Daml)

4.1 `CoreState` — the singleton

4.2 Message publishing

4.3 VAA verification choice

4.4 Governance

4.5 Guardian-set expiry

4.6 Replay protection for integrators: a trie of consumed digests

4.7 Addressing without keys: the disclosure service

5. On-chain signature verification (the crux)

Making verification hint-free for integrators (recommended)

Validation status

6. Consistency / finality

7. Off-chain design (the watcher)

7.1 `cantonclient` (Ledger API v2, gRPC)

7.2 `TxID` and offsets

7.3 `Run` loop (three goroutines, mirrors Sui)

7.4 Configuration

8. File map

9. Local development

Building & testing with `dpm`

Watcher integration test (dpm + Go)

End-to-end with Tilt

`guardianGovernance` external-party bootstrap

Status: opt-in while the k8s devnet path is validated

10. Trust model & deployment topology

11. Open Questions & Validation Items

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Wormhole Core Bridge & Watcher for Canton

1. Background: how Canton differs from EVM

2. Architecture overview

3. The VAA and the digest (unchanged across chains)

4. On-chain design (Daml)

4.1 CoreState — the singleton

4.2 Message publishing

4.3 VAA verification choice

4.4 Governance

4.5 Guardian-set expiry

4.6 Replay protection for integrators: a trie of consumed digests

4.7 Addressing without keys: the disclosure service

5. On-chain signature verification (the crux)

Making verification hint-free for integrators (recommended)

Validation status

6. Consistency / finality

7. Off-chain design (the watcher)

7.1 cantonclient (Ledger API v2, gRPC)

7.2 TxID and offsets

7.3 Run loop (three goroutines, mirrors Sui)

7.4 Configuration

8. File map

9. Local development

Building & testing with dpm

Watcher integration test (dpm + Go)

End-to-end with Tilt

guardianGovernance external-party bootstrap

Status: opt-in while the k8s devnet path is validated

10. Trust model & deployment topology

11. Open Questions & Validation Items

4.1 `CoreState` — the singleton

7.1 `cantonclient` (Ledger API v2, gRPC)

7.2 `TxID` and offsets

7.3 `Run` loop (three goroutines, mirrors Sui)

Building & testing with `dpm`

`guardianGovernance` external-party bootstrap