eth-offline

commit 6802d8018d8b85e7e119a0f1d136a0cdb21c664a
Author: lash <dev@holbrook.no>
Date:   Mon, 13 Mar 2023 12:12:17 +0000

Initial commit

Diffstat:
A
solidity/OfflineMinter.sol
 | 
94
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

1 file changed, 94 insertions(+), 0 deletions(-)
diff --git a/solidity/OfflineMinter.sol b/solidity/OfflineMinter.sol
@@ -0,0 +1,94 @@
+pragma solidity ^0.8.0;
+
+contract OfflineMinter {
+
+	bytes26 constant prefix = bytes26(abi.encodePacked("0x19457468657265756d205369676e6564204d6573736167653a0a"));
+
+	function verifyRequest(address _owner, bytes memory _data, bytes memory _signature) public pure returns(bool) {
+		address beneficiary;
+		bytes memory extra;
+		bytes memory message;
+		bytes32 messageDigest;
+		string memory messageLength;
+		uint256 messageLengthLength;
+
+		(beneficiary, extra) = splitData(_data);
+		messageLength = uintToString(uint(_data.length));
+		messageLengthLength = bytes(messageLength).length;
+
+		message = new bytes(_data.length + 26 + messageLengthLength);
+		messageDigest = keccak256(abi.encodePacked(prefix, messageLength, _data));
+
+		return _owner == recoverSigner(messageDigest, _signature);
+	}
+
+	function splitData(bytes memory _data) public pure returns(address _beneficiary, bytes memory _extra) {
+		bytes memory beneficiary;
+		bytes memory extra;
+
+		require(_data.length > 20, 'ERR_CONTENTS');
+
+		beneficiary = new bytes(20);
+		extra = new bytes(_data.length - 20);
+
+		for (uint256 i; i < beneficiary.length; i++) {
+			beneficiary[i] = _data[i];
+		}
+		for (uint256 i; i < extra.length; i++) {
+			extra[i] = _data[i+20];
+		}
+		verifyExtraData(extra);
+		return (address(bytes20(beneficiary)), extra);
+	}
+
+	function verifyExtraData(bytes memory _data) public pure {
+		revert('verification not implemented');
+	}
+
+	// from https://solidity-by-example.org/signature/
+	function recoverSigner(bytes32 _ethSignedMessageHash, bytes memory _signature) public pure returns (address) {
+		(bytes32 r, bytes32 s, uint8 v) = splitSignature(_signature);
+		return ecrecover(_ethSignedMessageHash, v, r, s);
+	}
+
+	// from https://solidity-by-example.org/signature/
+	function splitSignature(bytes memory sig) public pure returns (bytes32 r, bytes32 s, uint8 v) {
+		require(sig.length == 65, "invalid signature length");
+
+		assembly {
+		    /*
+		    First 32 bytes stores the length of the signature
+
+		    add(sig, 32) = pointer of sig + 32
+		    effectively, skips first 32 bytes of signature
+
+		    mload(p) loads next 32 bytes starting at the memory address p into memory
+		    */
+
+		    // first 32 bytes, after the length prefix
+		    r := mload(add(sig, 32))
+		    // second 32 bytes
+		    s := mload(add(sig, 64))
+		    // final byte (first byte of the next 32 bytes)
+		    v := byte(0, mload(add(sig, 96)))
+		}
+
+		// implicitly return (r, s, v)
+	}
+
+	function uintToString(uint v) public pure returns (string memory str) {
+		uint maxlength = 100;
+		bytes memory reversed = new bytes(maxlength);
+		uint i = 0;
+		while (v != 0) {
+		    uint remainder = v % 10;
+		    v = v / 10;
+		    reversed[i++] = bytes1(bytes32(48 + remainder));
+		}
+		bytes memory s = new bytes(i);
+		for (uint j = 0; j < i; j++) {
+		    s[j] = reversed[i - 1 - j];
+		}
+		str = string(s);
+	}
+}