fixed #178

Author: aalavandhan

contracts/UFragments.sol

@@ -76,6 +76,34 @@ contract UFragments is ERC20Detailed, Ownable {
     // it's fully paid.
     mapping(address => mapping(address => uint256)) private _allowedFragments;
 
+    // EIP-2612: permit – 712-signed approvals
+    // https://eips.ethereum.org/EIPS/eip-2612
+    bytes public constant EIP712_REVISION = "1";
+    bytes32 internal constant EIP712_DOMAIN =
+        keccak256(
+            "EIP712Domain(string name,string version,uint256 chainId,address verifyingContract)"
+        );
+    bytes32 public constant PERMIT_TYPEHASH =
+        keccak256(
+            "Permit(address owner,address spender,uint256 value,uint256 nonce,uint256 deadline)"
+        );
+    bytes32 public constant DOMAIN_SEPARATOR =
+        keccak256(
+            abi.encode(
+                EIP712_DOMAIN,
+                // hardcoding token name
+                keccak256("Ampleforth"),
+                keccak256(EIP712_REVISION),
+                // hardcoding Ethereum chainId
+                uint256(1),
+                // hardcoding Ampleforth ethereum address
+                address(0xD46bA6D942050d489DBd938a2C909A5d5039A161)
+            )
+        );
+
+    // EIP-2612: keeps track of number of permits per address
+    mapping(address => uint256) private _nonces;
+
     /**
      * @param monetaryPolicy_ The address of the monetary policy contract to use for authentication.
      */
@@ -155,6 +183,14 @@ contract UFragments is ERC20Detailed, Ownable {
         return _gonBalances[who].div(_gonsPerFragment);
     }
 
+    /**
+     * @param who The address to query.
+     * @return The number of successful permits by the specified address.
+     */
+    function nonces(address who) public view returns (uint256) {
+        return _nonces[who];
+    }
+
     /**
      * @dev Transfer tokens to a specified address.
      * @param to The address to transfer to.
@@ -255,4 +291,53 @@ contract UFragments is ERC20Detailed, Ownable {
         emit Approval(msg.sender, spender, _allowedFragments[msg.sender][spender]);
         return true;
     }
+
+    /**
+     * @dev Allows for approvals to be made via secp256k1 signatures.
+     * @param owner The owner of the funds
+     * @param spender The spender
+     * @param value The amount
+     * @param deadline The deadline timestamp, type(uint256).max for max deadline
+     * @param v Signature param
+     * @param s Signature param
+     * @param r Signature param
+     */
+    function permit(
+        address owner,
+        address spender,
+        uint256 value,
+        uint256 deadline,
+        uint8 v,
+        bytes32 r,
+        bytes32 s
+    ) public {
+        //solium-disable-next-line
+        require(block.timestamp <= deadline);
+
+        uint256 currentValidNonce = _nonces[owner];
+        bytes32 digest =
+            keccak256(
+                abi.encodePacked(
+                    "\x19\x01",
+                    DOMAIN_SEPARATOR,
+                    keccak256(
+                        abi.encode(
+                            PERMIT_TYPEHASH,
+                            owner,
+                            spender,
+                            value,
+                            currentValidNonce,
+                            deadline
+                        )
+                    )
+                )
+            );
+
+        require(owner == ecrecover(digest, v, r, s));
+
+        _nonces[owner] = currentValidNonce.add(1);
+
+        _allowedFragments[owner][spender] = value;
+        emit Approval(owner, spender, value);
+    }
 }

package.json

@@ -38,6 +38,8 @@
     "bignumber.js": "^9.0.0",
     "chai": "^4.2.0",
     "ethereum-waffle": "^3.2.1",
+    "ethereumjs-util": "^7.0.7",
+    "ethereumjs-wallet": "^1.0.1",
     "ethers": "^5.0.24",
     "hardhat": "^2.0.6",
     "pre-commit": "^1.2.2",

test/unit/UFragments.ts

@@ -1,15 +1,53 @@
 import { ethers, upgrades } from 'hardhat'
-import { Contract, Signer, BigNumber } from 'ethers'
+import { Contract, Signer, BigNumber, BigNumberish } from 'ethers'
 import { expect } from 'chai'
+import { fromRpcSig } from 'ethereumjs-util'
+import { TypedDataUtils, signTypedMessage, TypedMessage } from 'eth-sig-util'
+import { default as Wallet } from 'ethereumjs-wallet'
 
 const toUFrgDenomination = (ample: string): BigNumber =>
   ethers.utils.parseUnits(ample, DECIMALS)
 
+const ETHEREUM_CHAIN_ID = 1
+const ETHEREUM_AMPL_ADDRESS = '0xD46bA6D942050d489DBd938a2C909A5d5039A161'
+const EIP712_REVISION = '1'
+
+const TOKEN_NAME = 'Ampleforth'
+const TOKEN_SYMBOL = 'AMPL'
 const DECIMALS = 9
 const INITIAL_SUPPLY = ethers.utils.parseUnits('50', 6 + DECIMALS)
 const transferAmount = toUFrgDenomination('10')
 const unitTokenAmount = toUFrgDenomination('1')
 
+const EIP712Domain = [
+  { name: 'name', type: 'string' },
+  { name: 'version', type: 'string' },
+  { name: 'chainId', type: 'uint256' },
+  { name: 'verifyingContract', type: 'address' },
+]
+const Permit = [
+  { name: 'owner', type: 'address' },
+  { name: 'spender', type: 'address' },
+  { name: 'value', type: 'uint256' },
+  { name: 'nonce', type: 'uint256' },
+  { name: 'deadline', type: 'uint256' },
+]
+function domainSeparator(
+  name: string,
+  version: string,
+  chainId: number,
+  verifyingContract: string,
+): string {
+  return (
+    '0x' +
+    TypedDataUtils.hashStruct(
+      'EIP712Domain',
+      { name, version, chainId, verifyingContract },
+      { EIP712Domain },
+    ).toString('hex')
+  )
+}
+
 let accounts: Signer[],
   deployer: Signer,
   uFragments: Contract,
@@ -19,6 +57,7 @@ async function setupContracts() {
   // prepare signers
   accounts = await ethers.getSigners()
   deployer = accounts[0]
+
   // deploy upgradable token
   const factory = await ethers.getContractFactory('UFragments')
   uFragments = await upgrades.deployProxy(
@@ -60,10 +99,113 @@ describe('UFragments:Initialization', () => {
   })
 
   it('should set detailed ERC20 parameters', async function () {
-    expect(await uFragments.name()).to.eq('Ampleforth')
-    expect(await uFragments.symbol()).to.eq('AMPL')
+    expect(await uFragments.name()).to.eq(TOKEN_NAME)
+    expect(await uFragments.symbol()).to.eq(TOKEN_SYMBOL)
     expect(await uFragments.decimals()).to.eq(DECIMALS)
   })
+
+  it('should set the EIP2612 parameters', async function () {
+    expect(await uFragments.EIP712_REVISION()).to.eq('0x31')
+    expect(await uFragments.PERMIT_TYPEHASH()).to.eq(
+      '0x6e71edae12b1b97f4d1f60370fef10105fa2faae0126114a169c64845d6126c9',
+    )
+    // with hard-coded parameters
+    expect(await uFragments.DOMAIN_SEPARATOR()).to.eq(
+      domainSeparator(
+        TOKEN_NAME,
+        '1',
+        ETHEREUM_CHAIN_ID,
+        ETHEREUM_AMPL_ADDRESS,
+      ),
+    )
+  })
+
+  it('initial nonce is 0', async function () {
+    expect(await uFragments.nonces(await deployer.getAddress())).to.eq('0')
+  })
+})
+
+// Using the cases specified by:
+// https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/test/drafts/ERC20Permit.test.js
+describe('UFragments:EIP-2612 Permit', () => {
+  let wallet: Wallet, owner: string, spender: string, nonce: number
+
+  const value = 42
+  const maxDeadline = 99999999999
+
+  beforeEach('setup UFragments contract', async function () {
+    await setupContracts()
+
+    wallet = Wallet.generate()
+    owner = wallet.getAddressString()
+    spender = Wallet.generate().getAddressString()
+    nonce = 0
+  })
+
+  describe('permit', function () {
+    const buildPermitData = (
+      deadline: number = maxDeadline,
+    ): TypedMessage<any> => {
+      return {
+        primaryType: 'Permit',
+        types: { EIP712Domain, Permit },
+        domain: {
+          name: TOKEN_NAME,
+          version: EIP712_REVISION,
+          chainId: ETHEREUM_CHAIN_ID,
+          verifyingContract: ETHEREUM_AMPL_ADDRESS,
+        },
+        message: { owner, spender, value, nonce, deadline },
+      }
+    }
+
+    it('accepts owner signature', async function () {
+      const data = buildPermitData()
+      const signature = signTypedMessage(wallet.getPrivateKey(), { data })
+      const { v, r, s } = fromRpcSig(signature)
+      const receipt = await uFragments
+        .connect(deployer)
+        .permit(owner, spender, value, maxDeadline, v, r, s)
+      expect(await uFragments.nonces(owner)).to.eq('1')
+      expect(await uFragments.allowance(owner, spender)).to.eq(value)
+    })
+
+    it('rejects reused signature', async function () {
+      const data = buildPermitData()
+      const signature = signTypedMessage(wallet.getPrivateKey(), { data })
+      const { v, r, s } = fromRpcSig(signature)
+      await uFragments
+        .connect(deployer)
+        .permit(owner, spender, value, maxDeadline, v, r, s)
+      await expect(
+        uFragments
+          .connect(deployer)
+          .permit(owner, spender, value, maxDeadline, v, r, s),
+      ).to.be.reverted
+    })
+
+    it('rejects other signature', async function () {
+      const otherWallet = Wallet.generate()
+      const data = buildPermitData()
+      const signature = signTypedMessage(otherWallet.getPrivateKey(), { data })
+      const { v, r, s } = fromRpcSig(signature)
+      await expect(
+        uFragments
+          .connect(deployer)
+          .permit(owner, spender, value, maxDeadline, v, r, s),
+      ).to.be.reverted
+    })
+
+    it('rejects expired permit', async function () {
+      const deadline =
+        (await ethers.provider.getBlock('latest')).timestamp - 3600 * 24 * 7
+      const data = buildPermitData(deadline)
+      const signature = signTypedMessage(wallet.getPrivateKey(), { data })
+      const { v, r, s } = fromRpcSig(signature)
+      await expect(uFragments.permit(owner, spender, value, deadline, v, r, s))
+        .to.be.reverted
+    })
+  })
 })
 
 describe('UFragments:setMonetaryPolicy', async () => {

yarn.lock

@@ -3316,7 +3316,7 @@ ethereumjs-util@^5.0.0, ethereumjs-util@^5.0.1, ethereumjs-util@^5.1.1, ethereum
     rlp "^2.0.0"
     safe-buffer "^5.1.1"
 
-ethereumjs-util@^7.0.2, ethereumjs-util@^7.0.3:
+ethereumjs-util@^7.0.2, ethereumjs-util@^7.0.3, ethereumjs-util@^7.0.7:
   version "7.0.7"
   resolved "https://registry.yarnpkg.com/ethereumjs-util/-/ethereumjs-util-7.0.7.tgz#484fb9c03b766b2ee64821281070616562fb5a59"
   integrity sha512-vU5rtZBlZsgkTw3o6PDKyB8li2EgLavnAbsKcfsH2YhHH1Le+PP8vEiMnAnvgc1B6uMoaM5GDCrVztBw0Q5K9g==
@@ -3381,6 +3381,20 @@ [email protected]:
     utf8 "^3.0.0"
     uuid "^3.3.2"
 
+ethereumjs-wallet@^1.0.1:
+  version "1.0.1"
+  resolved "https://registry.yarnpkg.com/ethereumjs-wallet/-/ethereumjs-wallet-1.0.1.tgz#664a4bcacfc1291ca2703de066df1178938dba1c"
+  integrity sha512-3Z5g1hG1das0JWU6cQ9HWWTY2nt9nXCcwj7eXVNAHKbo00XAZO8+NHlwdgXDWrL0SXVQMvTWN8Q/82DRH/JhPw==
+  dependencies:
+    aes-js "^3.1.1"
+    bs58check "^2.1.2"
+    ethereum-cryptography "^0.1.3"
+    ethereumjs-util "^7.0.2"
+    randombytes "^2.0.6"
+    scrypt-js "^3.0.1"
+    utf8 "^3.0.0"
+    uuid "^3.3.2"
+
 ethers@^4.0.32:
   version "4.0.48"
   resolved "https://registry.yarnpkg.com/ethers/-/ethers-4.0.48.tgz#330c65b8133e112b0613156e57e92d9009d8fbbe"