/**
* @dev Checks whether the signature provided is valid for the provided data, hash. Will revert otherwise.
* @param dataHash Hash of the data (could be either a message hash or transaction hash)
* @param data That should be signed (this is passed to an external validator contract)
* @param signatures Signature data that should be verified. Can be ECDSA signature, contract signature (EIP-1271) or approved hash.
* @param requiredSignatures Amount of required valid signatures.
*/
function checkNSignatures(
bytes32 dataHash,
bytes memory data,
bytes memory signatures,
uint256 requiredSignatures
) public view {
// Check that the provided signature data is not too short
require(signatures.length >= requiredSignatures.mul(65), "GS020");
// There cannot be an owner with address 0.
address lastOwner = address(0);
address currentOwner;
uint8 v;
bytes32 r;
bytes32 s;
uint256 i;
for (i = 0; i < requiredSignatures; i++) {
(v, r, s) = signatureSplit(signatures, i);
if (v == 0) {
// If v is 0 then it is a contract signature
// When handling contract signatures the address of the contract is encoded into r
currentOwner = address(uint160(uint256(r)));
// Check that signature data pointer (s) is not pointing inside the static part of the signatures bytes
// This check is not completely accurate, since it is possible that more signatures than the threshold are send.
// Here we only check that the pointer is not pointing inside the part that is being processed
require(uint256(s) >= requiredSignatures.mul(65), "GS021");
// Check that signature data pointer (s) is in bounds (points to the length of data -> 32 bytes)
require(uint256(s).add(32) <= signatures.length, "GS022");
// Check if the contract signature is in bounds: start of data is s + 32 and end is start + signature length
uint256 contractSignatureLen;
// solhint-disable-next-line no-inline-assembly
assembly {
contractSignatureLen := mload(add(add(signatures, s), 0x20))
}
require(uint256(s).add(32).add(contractSignatureLen) <= signatures.length, "GS023");
// Check signature
bytes memory contractSignature;
// solhint-disable-next-line no-inline-assembly
assembly {
// The signature data for contract signatures is appended to the concatenated signatures and the offset is stored in s
contractSignature := add(add(signatures, s), 0x20)
}
require(ISignatureValidator(currentOwner).isValidSignature(data, contractSignature) == EIP1271_MAGIC_VALUE, "GS024");
} else if (v == 1) {
// If v is 1 then it is an approved hash
// When handling approved hashes the address of the approver is encoded into r
currentOwner = address(uint160(uint256(r)));
// Hashes are automatically approved by the sender of the message or when they have been pre-approved via a separate transaction
require(msg.sender == currentOwner || approvedHashes[currentOwner][dataHash] != 0, "GS025");
} else if (v > 30) {
// If v > 30 then default va (27,28) has been adjusted for eth_sign flow
// To support eth_sign and similar we adjust v and hash the messageHash with the Ethereum message prefix before applying ecrecover
currentOwner = ecrecover(keccak256(abi.encodePacked("\x19Ethereum Signed Message:\n32", dataHash)), v - 4, r, s);
} else {
// Default is the ecrecover flow with the provided data hash
// Use ecrecover with the messageHash for EOA signatures
currentOwner = ecrecover(dataHash, v, r, s);
}
require(currentOwner > lastOwner && owners[currentOwner] != address(0) && currentOwner != SENTINEL_OWNERS, "GS026");
lastOwner = currentOwner;
}
}