515 lines
20 KiB
Solidity
515 lines
20 KiB
Solidity
pragma solidity ^0.4.17;
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/// general helpers.
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/// `internal` so they get compiled into contracts using them.
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library Helpers {
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/// returns whether `array` contains `value`.
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function addressArrayContains(address[] array, address value) internal pure returns (bool) {
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for (uint i = 0; i < array.length; i++) {
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if (array[i] == value) {
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return true;
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}
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}
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return false;
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}
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// returns the digits of `inputValue` as a string.
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// example: `uintToString(12345678)` returns `"12345678"`
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function uintToString(uint inputValue) internal pure returns (string) {
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// figure out the length of the resulting string
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uint length = 0;
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uint currentValue = inputValue;
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do {
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length++;
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currentValue /= 10;
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} while (currentValue != 0);
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// allocate enough memory
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bytes memory result = new bytes(length);
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// construct the string backwards
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uint i = length - 1;
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currentValue = inputValue;
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do {
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result[i--] = byte(48 + currentValue % 10);
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currentValue /= 10;
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} while (currentValue != 0);
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return string(result);
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}
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/// returns whether signatures (whose components are in `vs`, `rs`, `ss`)
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/// contain `requiredSignatures` distinct correct signatures
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/// where signer is in `allowed_signers`
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/// that signed `message`
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function hasEnoughValidSignatures(bytes message, uint8[] vs, bytes32[] rs, bytes32[] ss, address[] allowed_signers, uint requiredSignatures) internal pure returns (bool) {
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// not enough signatures
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if (vs.length < requiredSignatures) {
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return false;
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}
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var hash = MessageSigning.hashMessage(message);
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var encountered_addresses = new address[](allowed_signers.length);
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for (uint i = 0; i < requiredSignatures; i++) {
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var recovered_address = ecrecover(hash, vs[i], rs[i], ss[i]);
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// only signatures by addresses in `addresses` are allowed
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if (!addressArrayContains(allowed_signers, recovered_address)) {
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return false;
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}
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// duplicate signatures are not allowed
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if (addressArrayContains(encountered_addresses, recovered_address)) {
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return false;
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}
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encountered_addresses[i] = recovered_address;
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}
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return true;
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}
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}
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/// Library used only to test Helpers library via rpc calls
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library HelpersTest {
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function addressArrayContains(address[] array, address value) public pure returns (bool) {
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return Helpers.addressArrayContains(array, value);
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}
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function uintToString(uint256 inputValue) public pure returns (string str) {
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return Helpers.uintToString(inputValue);
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}
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function hasEnoughValidSignatures(bytes message, uint8[] vs, bytes32[] rs, bytes32[] ss, address[] addresses, uint requiredSignatures) public pure returns (bool) {
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return Helpers.hasEnoughValidSignatures(message, vs, rs, ss, addresses, requiredSignatures);
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}
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}
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// helpers for message signing.
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// `internal` so they get compiled into contracts using them.
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library MessageSigning {
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function recoverAddressFromSignedMessage(bytes signature, bytes message) internal pure returns (address) {
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require(signature.length == 65);
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bytes32 r;
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bytes32 s;
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bytes1 v;
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// solium-disable-next-line security/no-inline-assembly
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assembly {
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r := mload(add(signature, 0x20))
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s := mload(add(signature, 0x40))
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v := mload(add(signature, 0x60))
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}
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return ecrecover(hashMessage(message), uint8(v), r, s);
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}
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function hashMessage(bytes message) internal pure returns (bytes32) {
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bytes memory prefix = "\x19Ethereum Signed Message:\n";
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return keccak256(prefix, Helpers.uintToString(message.length), message);
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}
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}
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/// Library used only to test MessageSigning library via rpc calls
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library MessageSigningTest {
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function recoverAddressFromSignedMessage(bytes signature, bytes message) public pure returns (address) {
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return MessageSigning.recoverAddressFromSignedMessage(signature, message);
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}
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}
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library Message {
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// layout of message :: bytes:
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// offset 0: 32 bytes :: uint (little endian) - message length
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// offset 32: 20 bytes :: address - recipient address
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// offset 52: 32 bytes :: uint (little endian) - value
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// offset 84: 32 bytes :: bytes32 - transaction hash
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// offset 116: 32 bytes :: uint (little endian) - home gas price
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// bytes 1 to 32 are 0 because message length is stored as little endian.
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// mload always reads 32 bytes.
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// so we can and have to start reading recipient at offset 20 instead of 32.
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// if we were to read at 32 the address would contain part of value and be corrupted.
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// when reading from offset 20 mload will read 12 zero bytes followed
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// by the 20 recipient address bytes and correctly convert it into an address.
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// this saves some storage/gas over the alternative solution
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// which is padding address to 32 bytes and reading recipient at offset 32.
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// for more details see discussion in:
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// https://github.com/paritytech/parity-bridge/issues/61
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function getRecipient(bytes message) internal pure returns (address) {
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address recipient;
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// solium-disable-next-line security/no-inline-assembly
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assembly {
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recipient := mload(add(message, 20))
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}
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return recipient;
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}
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function getValue(bytes message) internal pure returns (uint) {
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uint value;
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// solium-disable-next-line security/no-inline-assembly
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assembly {
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value := mload(add(message, 52))
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}
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return value;
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}
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function getTransactionHash(bytes message) internal pure returns (bytes32) {
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bytes32 hash;
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// solium-disable-next-line security/no-inline-assembly
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assembly {
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hash := mload(add(message, 84))
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}
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return hash;
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}
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function getHomeGasPrice(bytes message) internal pure returns (uint) {
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uint gasPrice;
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// solium-disable-next-line security/no-inline-assembly
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assembly {
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gasPrice := mload(add(message, 116))
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}
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return gasPrice;
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}
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}
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/// Library used only to test Message library via rpc calls
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library MessageTest {
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function getRecipient(bytes message) public pure returns (address) {
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return Message.getRecipient(message);
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}
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function getValue(bytes message) public pure returns (uint) {
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return Message.getValue(message);
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}
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function getTransactionHash(bytes message) public pure returns (bytes32) {
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return Message.getTransactionHash(message);
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}
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function getHomeGasPrice(bytes message) public pure returns (uint) {
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return Message.getHomeGasPrice(message);
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}
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}
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contract HomeBridge {
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/// Number of authorities signatures required to withdraw the money.
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///
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/// Must be lesser than number of authorities.
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uint public requiredSignatures;
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/// The gas cost of calling `HomeBridge.withdraw`.
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///
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/// Is subtracted from `value` on withdraw.
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/// recipient pays the relaying authority for withdraw.
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/// this shuts down attacks that exhaust authorities funds on home chain.
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uint public estimatedGasCostOfWithdraw;
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/// Contract authorities.
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address[] public authorities;
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/// Used foreign transaction hashes.
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mapping (bytes32 => bool) withdraws;
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/// Event created on money deposit.
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event Deposit (address recipient, uint value);
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/// Event created on money withdraw.
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event Withdraw (address recipient, uint value);
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/// Constructor.
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function HomeBridge(
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uint requiredSignaturesParam,
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address[] authoritiesParam,
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uint estimatedGasCostOfWithdrawParam
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) public
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{
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require(requiredSignaturesParam != 0);
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require(requiredSignaturesParam <= authoritiesParam.length);
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requiredSignatures = requiredSignaturesParam;
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authorities = authoritiesParam;
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estimatedGasCostOfWithdraw = estimatedGasCostOfWithdrawParam;
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}
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/// Should be used to deposit money.
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function () public payable {
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Deposit(msg.sender, msg.value);
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}
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/// final step of a withdraw.
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/// checks that `requiredSignatures` `authorities` have signed of on the `message`.
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/// then transfers `value` to `recipient` (both extracted from `message`).
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/// see message library above for a breakdown of the `message` contents.
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/// `vs`, `rs`, `ss` are the components of the signatures.
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/// anyone can call this, provided they have the message and required signatures!
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/// only the `authorities` can create these signatures.
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/// `requiredSignatures` authorities can sign arbitrary `message`s
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/// transfering any ether `value` out of this contract to `recipient`.
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/// bridge users must trust a majority of `requiredSignatures` of the `authorities`.
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function withdraw(uint8[] vs, bytes32[] rs, bytes32[] ss, bytes message) public {
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require(message.length == 116);
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// check that at least `requiredSignatures` `authorities` have signed `message`
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require(Helpers.hasEnoughValidSignatures(message, vs, rs, ss, authorities, requiredSignatures));
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address recipient = Message.getRecipient(message);
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uint value = Message.getValue(message);
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bytes32 hash = Message.getTransactionHash(message);
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uint homeGasPrice = Message.getHomeGasPrice(message);
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// if the recipient calls `withdraw` they can choose the gas price freely.
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// if anyone else calls `withdraw` they have to use the gas price
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// `homeGasPrice` specified by the user initiating the withdraw.
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// this is a security mechanism designed to shut down
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// malicious senders setting extremely high gas prices
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// and effectively burning recipients withdrawn value.
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// see https://github.com/paritytech/parity-bridge/issues/112
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// for further explanation.
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require((recipient == msg.sender) || (tx.gasprice == homeGasPrice));
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// The following two statements guard against reentry into this function.
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// Duplicated withdraw or reentry.
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require(!withdraws[hash]);
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// Order of operations below is critical to avoid TheDAO-like re-entry bug
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withdraws[hash] = true;
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uint estimatedWeiCostOfWithdraw = estimatedGasCostOfWithdraw * homeGasPrice;
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// charge recipient for relay cost
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uint valueRemainingAfterSubtractingCost = value - estimatedWeiCostOfWithdraw;
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// pay out recipient
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recipient.transfer(valueRemainingAfterSubtractingCost);
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// refund relay cost to relaying authority
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msg.sender.transfer(estimatedWeiCostOfWithdraw);
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Withdraw(recipient, valueRemainingAfterSubtractingCost);
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}
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}
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contract ForeignBridge {
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// following is the part of ForeignBridge that implements an ERC20 token.
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// ERC20 spec: https://github.com/ethereum/EIPs/blob/master/EIPS/eip-20-token-standard.md
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uint public totalSupply;
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string public name = "ForeignBridge";
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/// maps addresses to their token balances
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mapping (address => uint) public balances;
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// owner of account approves the transfer of an amount by another account
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mapping(address => mapping (address => uint)) allowed;
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/// Event created on money transfer
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event Transfer(address indexed from, address indexed to, uint tokens);
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// returns the ERC20 token balance of the given address
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function balanceOf(address tokenOwner) public view returns (uint) {
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return balances[tokenOwner];
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}
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/// Transfer `value` to `recipient` on this `foreign` chain.
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///
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/// does not affect `home` chain. does not do a relay.
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/// as specificed in ERC20 this doesn't fail if tokens == 0.
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function transfer(address recipient, uint tokens) public returns (bool) {
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require(balances[msg.sender] >= tokens);
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// fails if there is an overflow
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require(balances[recipient] + tokens >= balances[recipient]);
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balances[msg.sender] -= tokens;
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balances[recipient] += tokens;
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Transfer(msg.sender, recipient, tokens);
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return true;
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}
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// following is the part of ForeignBridge that is concerned
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// with the part of the ERC20 standard responsible for giving others spending rights
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// and spending others tokens
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// created when `approve` is executed to mark that
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// `tokenOwner` has approved `spender` to spend `tokens` of his tokens
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event Approval(address indexed tokenOwner, address indexed spender, uint tokens);
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// allow `spender` to withdraw from your account, multiple times, up to the `tokens` amount.
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// calling this function repeatedly overwrites the current allowance.
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function approve(address spender, uint tokens) public returns (bool) {
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allowed[msg.sender][spender] = tokens;
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Approval(msg.sender, spender, tokens);
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return true;
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}
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// returns how much `spender` is allowed to spend of `owner`s tokens
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function allowance(address owner, address spender) public view returns (uint256) {
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return allowed[owner][spender];
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}
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function transferFrom(address from, address to, uint tokens) public returns (bool) {
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// `from` has enough tokens
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require(balances[from] >= tokens);
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// `sender` is allowed to move `tokens` from `from`
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require(allowed[from][msg.sender] >= tokens);
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// fails if there is an overflow
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require(balances[to] + tokens >= balances[to]);
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balances[to] += tokens;
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balances[from] -= tokens;
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allowed[from][msg.sender] -= tokens;
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Transfer(from, to, tokens);
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return true;
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}
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// following is the part of ForeignBridge that is
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// no longer part of ERC20 and is concerned with
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// with moving tokens from and to HomeBridge
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struct SignaturesCollection {
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/// Signed message.
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bytes message;
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/// Authorities who signed the message.
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address[] signed;
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/// Signatures
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bytes[] signatures;
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}
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/// Number of authorities signatures required to withdraw the money.
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///
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/// Must be less than number of authorities.
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uint public requiredSignatures;
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uint public estimatedGasCostOfWithdraw;
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/// Contract authorities.
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address[] public authorities;
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/// Pending deposits and authorities who confirmed them
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mapping (bytes32 => address[]) deposits;
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/// Pending signatures and authorities who confirmed them
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mapping (bytes32 => SignaturesCollection) signatures;
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/// triggered when relay of deposit from HomeBridge is complete
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event Deposit(address recipient, uint value);
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/// Event created on money withdraw.
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event Withdraw(address recipient, uint value, uint homeGasPrice);
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/// Collected signatures which should be relayed to home chain.
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event CollectedSignatures(address authorityResponsibleForRelay, bytes32 messageHash);
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function ForeignBridge(
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uint _requiredSignatures,
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address[] _authorities,
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uint _estimatedGasCostOfWithdraw
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) public
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{
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require(_requiredSignatures != 0);
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require(_requiredSignatures <= _authorities.length);
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requiredSignatures = _requiredSignatures;
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authorities = _authorities;
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estimatedGasCostOfWithdraw = _estimatedGasCostOfWithdraw;
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}
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/// require that sender is an authority
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modifier onlyAuthority() {
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require(Helpers.addressArrayContains(authorities, msg.sender));
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_;
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}
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/// Used to deposit money to the contract.
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///
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/// deposit recipient (bytes20)
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/// deposit value (uint)
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/// mainnet transaction hash (bytes32) // to avoid transaction duplication
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function deposit(address recipient, uint value, bytes32 transactionHash) public onlyAuthority() {
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// Protection from misbehaving authority
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var hash = keccak256(recipient, value, transactionHash);
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// don't allow authority to confirm deposit twice
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require(!Helpers.addressArrayContains(deposits[hash], msg.sender));
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deposits[hash].push(msg.sender);
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// TODO: this may cause troubles if requiredSignatures len is changed
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if (deposits[hash].length == requiredSignatures) {
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balances[recipient] += value;
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// mints tokens
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totalSupply += value;
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// ERC20 specifies: a token contract which creates new tokens
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// SHOULD trigger a Transfer event with the _from address
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// set to 0x0 when tokens are created.
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Transfer(0x0, recipient, value);
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Deposit(recipient, value);
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}
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}
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/// Transfer `value` from `msg.sender`s local balance (on `foreign` chain) to `recipient` on `home` chain.
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///
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/// immediately decreases `msg.sender`s local balance.
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/// emits a `Withdraw` event which will be picked up by the bridge authorities.
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/// bridge authorities will then sign off (by calling `submitSignature`) on a message containing `value`,
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/// `recipient` and the `hash` of the transaction on `foreign` containing the `Withdraw` event.
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/// once `requiredSignatures` are collected a `CollectedSignatures` event will be emitted.
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/// an authority will pick up `CollectedSignatures` an call `HomeBridge.withdraw`
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/// which transfers `value - relayCost` to `recipient` completing the transfer.
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function transferHomeViaRelay(address recipient, uint value, uint homeGasPrice) public {
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require(balances[msg.sender] >= value);
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// don't allow 0 value transfers to home
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require(value > 0);
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uint estimatedWeiCostOfWithdraw = estimatedGasCostOfWithdraw * homeGasPrice;
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require(value > estimatedWeiCostOfWithdraw);
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balances[msg.sender] -= value;
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// burns tokens
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totalSupply -= value;
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// in line with the transfer event from `0x0` on token creation
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// recommended by ERC20 (see implementation of `deposit` above)
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// we trigger a Transfer event to `0x0` on token destruction
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Transfer(msg.sender, 0x0, value);
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Withdraw(recipient, value, homeGasPrice);
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}
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/// Should be used as sync tool
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///
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/// Message is a message that should be relayed to main chain once authorities sign it.
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///
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/// for withdraw message contains:
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/// withdrawal recipient (bytes20)
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/// withdrawal value (uint)
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/// foreign transaction hash (bytes32) // to avoid transaction duplication
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function submitSignature(bytes signature, bytes message) public onlyAuthority() {
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// Validate submited signatures
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require(MessageSigning.recoverAddressFromSignedMessage(signature, message) == msg.sender);
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// Valid withdraw message must have 116 bytes
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require(message.length == 116);
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var hash = keccak256(message);
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// Duplicated signatures
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require(!Helpers.addressArrayContains(signatures[hash].signed, msg.sender));
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signatures[hash].message = message;
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signatures[hash].signed.push(msg.sender);
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signatures[hash].signatures.push(signature);
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// TODO: this may cause troubles if requiredSignatures len is changed
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if (signatures[hash].signed.length == requiredSignatures) {
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CollectedSignatures(msg.sender, hash);
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}
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}
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/// Get signature
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function signature(bytes32 hash, uint index) public view returns (bytes) {
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return signatures[hash].signatures[index];
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}
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/// Get message
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function message(bytes32 hash) public view returns (bytes) {
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return signatures[hash].message;
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}
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}
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