Add signature generation script

scripts/generateSig.js

@@ -0,0 +1,61 @@
+const ethUtil = require('ethereumjs-util');
+const sigUtil = require('eth-sig-util');
+const utils = sigUtil.TypedDataUtils;
+
+//Our lad Cal wants to send 2 dai to del, by signing a cheque and paying a 1 dai fee to msg.sender
+
+const calprivKeyHex = '4af1bceebf7f3634ec3cff8a2c38e51178d5d4ce585c52d6043e5e2cc3418bb0'
+const calprivKey = new Buffer.from(calprivKeyHex, 'hex')
+const cal = ethUtil.privateToAddress(calprivKey);
+const del = new Buffer.from('dd2d5d3f7f1b35b7a0601d6a00dbb7d44af58479', 'hex');
+const dai = new Buffer.from('E58d97b6622134C0436d60daeE7FBB8b965D9713', 'hex');
+console.log('cals address: ' + '0x' + cal.toString('hex'));
+console.log('dels address: ' + '0x' + del.toString('hex'));
+let typedData = {
+  types: {
+      EIP712Domain: [
+          { name: 'name', type: 'string' },
+          { name: 'version', type: 'string' },
+          { name: 'chainId', type: 'uint256' },
+          { name: 'verifyingContract', type: 'address' },
+      ],
+    Permit: [
+          { name: 'holder', type: 'address' },
+          { name: 'spender', type: 'address' },
+          { name: 'nonce', type: 'uint256' },
+          { name: 'expiry', type: 'uint256' },
+          { name: 'allowed', type: 'bool' },
+      ],
+  },
+  primaryType: 'Permit',
+  domain: {
+      name: 'Dai Stablecoin',
+      version: '1',
+      chainId: 99,
+      verifyingContract: '0xE58d97b6622134C0436d60daeE7FBB8b965D9713', //in hevm
+  },
+  message: {
+      holder: '0x'+cal.toString('hex'),
+      spender: '0x'+del.toString('hex'),
+      nonce: 0,
+      expiry: 604411200 + 3600,
+      allowed: true
+  },
+};
+
+let hash = ethUtil.bufferToHex(utils.hashStruct('EIP712Domain', typedData.domain, typedData.types))
+console.log('EIP712DomainHash: ' + hash);
+hash = ethUtil.bufferToHex(utils.hashType('Permit', typedData.types))
+console.log('Permit Typehash: ' + hash);
+hash = ethUtil.bufferToHex(utils.hashStruct('Permit', typedData.message, typedData.types))
+console.log('Permit (from cal to del) hash: ' + hash);
+const sig = sigUtil.signTypedData(calprivKey, { data: typedData });
+console.log('signed permit: ' + sig);
+
+let r = sig.slice(0,66);
+let s = '0x'+ sig.slice(66,130);
+let v = ethUtil.bufferToInt(ethUtil.toBuffer('0x'+sig.slice(130,132),'hex'));
+
+console.log('r: ' + r)
+console.log('s: ' + s)
+console.log('v: ' + v)