Split hash and sign

packages/waas/src/payloads/index.ts

@@ -15,7 +15,16 @@ export type Payload<T extends BasePacket> = {
   signatures: Signature[]
 }
 
+export function hashPacket(packet: Payload<BasePacket> | BasePacket): ethers.Bytes {
+  if ('version' in packet) {
+    packet = packet.packet
+  }
+
+  const encoded = ethers.utils.toUtf8Bytes(JSON.stringify(packet, null, 0))
+  return ethers.utils.arrayify(ethers.utils.keccak256(encoded))
+}
+
 export function signPacket(signer: ethers.Signer, packed: BasePacket): Promise<string> {
-  const encoded = ethers.utils.toUtf8Bytes(JSON.stringify(packed, null, 0))
-  return signer.signMessage(encoded)
+  const hash = hashPacket(packed)
+  return signer.signMessage(hash)
 }

packages/waas/tests/payloads.spec.ts

@@ -0,0 +1,39 @@
+import * as chai from 'chai'
+import { ethers } from 'ethers'
+
+import { Payload, hashPacket, signPacket } from '../src/payloads'
+import { TransactionsPacket } from '../src/payloads/wallet'
+
+const { expect } = chai
+
+describe('Payloads', () => {
+  it('Should sign a transactions payload', async () => {
+    const transactionsPacket: TransactionsPacket = {
+      code: 'sendTransactions',
+      wallet: '0xD67FC48b298B09Ed3D03403d930769C527186c4e',
+      chainId: 1,
+      transactions: [{
+        type: 'erc20send',
+        token: ethers.constants.AddressZero,
+        to: '0x0dc9603d4da53841C1C83f3B550C6143e60e0425',
+        value: '0'
+      }]
+    }
+
+    const sessionSigner = new ethers.Wallet('0xecd39e2cdadc2427255042ca7e0f86368bd7aa6e3c99470444b7d073840c1b51')
+    const sessionSignature = await signPacket(sessionSigner, transactionsPacket)
+
+    const payloads: Payload<TransactionsPacket> = {
+      version: '1',
+      packet: transactionsPacket,
+      signatures: [{
+        session: sessionSigner.address,
+        signature: sessionSignature
+      }]
+    }
+
+    const hash = hashPacket(payloads)
+    expect(ethers.utils.hexlify(hash)).to.equal('0xe54e41eca96c1c047ad6a31f80dd3e61ba5f8a6e0a8a83b95e58515afe1780da')
+    expect(sessionSignature).to.equal('0xd22e5853e09ea29812774fd658811aa6007781d3a7fa23bf5ab69d58cd18cd6467cf1a7969b982695e35db5514b90313c53a9eb941a986d572b35c5bd1d0a46f1b')
+  })
+})