fix: bind session vouchers to stored channel metadata

.changeset/veria-305-session-voucher-chain-binding.md

@@ -0,0 +1,5 @@
+---
+'mppx': patch
+---
+
+Bound session voucher verification to stored channel chain metadata.

src/tempo/server/Session.test.ts

@@ -668,6 +668,36 @@ describe.runIf(isLocalnet)('session', () => {
       expect(ch!.highestVoucherAmount).toBe(2000000n)
     })
 
+    test('rejects voucher signed for route escrow instead of stored channel escrow', async () => {
+      const { channelId, serializedTransaction } = await createSignedOpenTransaction(10000000n)
+      const server = createServer()
+      await openServerChannel(server, channelId, serializedTransaction)
+
+      const routeEscrow = '0x0000000000000000000000000000000000000999' as Address
+      const signature = await signVoucher(
+        client,
+        payer,
+        { channelId, cumulativeAmount: 2000000n },
+        routeEscrow,
+        chain.id,
+      )
+
+      await expect(
+        server.verify({
+          credential: {
+            challenge: makeChallenge({ id: 'route-escrow-replay', channelId }),
+            payload: {
+              action: 'voucher' as const,
+              channelId,
+              cumulativeAmount: '2000000',
+              signature,
+            },
+          },
+          request: makeRequest({ escrowContract: routeEscrow }),
+        }),
+      ).rejects.toThrow(InvalidSignatureError)
+    })
+
     test('rejects non-increasing voucher replay', async () => {
       const { channelId, serializedTransaction } = await createSignedOpenTransaction(10000000n)
       const server = createServer()

src/tempo/server/Session.ts

@@ -530,10 +530,8 @@ async function verifyAndAcceptVoucher(parameters: {
   channelId: Hex
   voucher: SignedVoucher
   onChain: OnChainChannel
-  methodDetails: SessionMethodDetails
 }): Promise<SessionReceipt> {
-  const { store, minVoucherDelta, challenge, channel, channelId, voucher, onChain, methodDetails } =
-    parameters
+  const { store, minVoucherDelta, challenge, channel, channelId, voucher, onChain } = parameters
 
   if (onChain.finalized) {
     throw new ChannelClosedError({ reason: 'channel is finalized on-chain' })
@@ -568,8 +566,8 @@ async function verifyAndAcceptVoucher(parameters: {
   }
 
   const isValid = await verifyVoucher(
-    methodDetails.escrowContract,
-    methodDetails.chainId,
+    channel.escrowContract,
+    channel.chainId,
     voucher,
     channel.authorizedSigner,
   )
@@ -848,11 +846,7 @@ async function handleVoucher(
 
   const onChain = await (async () => {
     if (isStale) {
-      const onChainChannel = await getOnChainChannel(
-        client,
-        methodDetails.escrowContract,
-        channelId,
-      )
+      const onChainChannel = await getOnChainChannel(client, channel.escrowContract, channelId)
       lastOnChainVerified.set(channelId, Date.now())
       // Persist closeRequestedAt so the cached path detects force-close
       // between re-queries.
@@ -883,7 +877,6 @@ async function handleVoucher(
     channelId,
     voucher,
     onChain,
-    methodDetails,
   })
 }
 
@@ -910,7 +903,7 @@ async function handleClose(
 
   const voucher = parseVoucherFromPayload(channelId, payload.cumulativeAmount, payload.signature)
 
-  const onChain = await getOnChainChannel(client, methodDetails.escrowContract, channelId)
+  const onChain = await getOnChainChannel(client, channel.escrowContract, channelId)
 
   if (onChain.finalized) {
     throw new ChannelClosedError({ reason: 'channel is finalized on-chain' })
@@ -936,8 +929,8 @@ async function handleClose(
   }
 
   const isValid = await verifyVoucher(
-    methodDetails.escrowContract,
-    methodDetails.chainId,
+    channel.escrowContract,
+    channel.chainId,
     voucher,
     channel.authorizedSigner,
   )
@@ -972,7 +965,7 @@ async function handleClose(
       sender: account?.address ?? client.account?.address,
     })
 
-    txHash = await closeOnChain(client, methodDetails.escrowContract, voucher, {
+    txHash = await closeOnChain(client, channel.escrowContract, voucher, {
       ...(feePayer && account ? { feePayer, account } : { account }),
       candidateFeeTokens: [channel.token],
     })