PCM_CCTF_challenge/flag_encoder/index.html

<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8"/>
		<title>CryptoCTF zero-knowledge flag-submission encoder v0.1</title>
		<script type="text/javascript" src="bn.js"></script>
		<script type="text/javascript" src="nano-ethereum-signer-mod.js"></script>
	</head>

	<body>

	<label for="inp-contestant-address">contestant's address:</label> <input id="inp-contestant-address" type="text" size="42" maxlength="42" pattern="0x[0-9a-fA-F]{40}" required placeholder="0x0000000000000000000000000000000000000000" autocomplete="cryptocurrency address" title="The cryptocurrency address of the contestant who is submitting the flag. It will be used as the message that is signed using an ECDSA signature scheme. It is incorporated to prevent submission forgery and theft. The resulting signature will be accepted by the CCTF smart-contract from only this address."/><br/>
	<label for="inp-flag">flag:</label> <input id="inp-flag" type="text" size="48" pattern="CCTF\{[ -~]*\}" required placeholder="CCTF{…}" autocomplete="flag" title="The flag for the challenge in question: a piece of data that can be found through solving the problem. It can be an outstanding character sequence of the form CCTF{…} that can be stumbled upon; otherwise its location/calculation (e.g. the deciphered message) and its formatting (e.g. hexadecimal) are precisely specified, and formatting always includes enclosing by CCTF{…}. The flag will be used as the secret key for signing using an ECDSA signature scheme." accesskey="f"/> <label for="outp-obscured-flag">⇒ obscured flag: </label><input id="outp-obscured-flag" type="text" size="42" maxlength="42" readonly title="The obscured flag: data to allow zero-knowledge verification of knowledge of the flag. It is the elliptic-curve public key related to the flag as the private key. It is the thing to be loaded into the CCTF smart-contract for the respective challenge."/><br />
	<label for="outp-signature">⇒ signature: </label><input id="outp-signature" type="text" size="132" maxlength="132" readonly title="The signature: a zero-knowledge proof of knowledge of the flag, bound to the given address. It's an ECDSA signature of the address as the message (hash) with the flag as the key. It is to be passed to the CCTF smart-contract's flag submission function."/><!--<br />
	<label for="inp-contract-address">CCTF smart-contract address:</label> <input id="inp-contract-address" type="text" size="42" maxlength="42" pattern="0x[0-9a-fA-F]{40}" placeholder="0x0000000000000000000000000000000000000000"/><br/>
	<label for="inp-contest-id">contest ID:</label> <input id="inp-contest-id" type="text" size="66" pattern="0x[0-9a-fA-F]+|[0-9]+" placeholder="0x0000000000000000000000000000000000000000000000000000000000000000"/><br/>
	<label for="inp-challenge-id">challenge ID:</label> <input id="inp-challenge-id" type="integer" size="4" placeholder="0" accesskey="c"/>-->

	<script type="text/javascript">
		var inpContestantAddress = document.querySelector("#inp-contestant-address");
		var inpFlag = document.querySelector("#inp-flag");
		var outpObscuredFlag = document.querySelector("#outp-obscured-flag");
		var outpSignature = document.querySelector("#outp-signature");
		var secp256k1n = new BN('115792089237316195423570985008687907852837564279074904382605163141518161494337', 10);

		function getPrivateKey() {
			var s = inpFlag.value;
			var h = "0x";
			if (s.slice(0, 5) !== "CCTF{" || s.slice(-1) !== "}")
				return null;
			for (i in s) {
				var c = s.charCodeAt(i);
				if (c < 32 || c > 126)
					return null;
				h += c.toString(16).padStart(2, "0");
			}
			return "0x" + new BN(keccak256(h).slice(2), 16).mod(secp256k1n.sub(new BN(1))).add(new BN(1)).toString(16).padStart(64, 0);
		}

		function updateOutputValues(ev) {
			var k = getPrivateKey();
			if (k === null) {
				outpObscuredFlag.value = "";
				outpSignature.value = "";
			} else {
				outpObscuredFlag.value = addressFromKey(k);
				var m = inpContestantAddress.value;
				if (!/^0x[0-9a-fA-F]{40}$/.test(m)) {
					outpSignature.value = "";
				} else {
					outpSignature.value = signMessage(m, k);
				}
			}
		}

		inpContestantAddress.oninput = updateOutputValues;
		inpFlag.oninput = updateOutputValues;

		updateOutputValues();
	</script>

	</body>
</html>
implement a proper flag encoder tool as an HTML+JS app 2023-08-20 01:20:23 +00:00			`<!DOCTYPE html>`
			`<html>`
			`<head>`
			`<meta charset="utf-8"/>`
			`<title>CryptoCTF zero-knowledge flag-submission encoder v0.1</title>`
add type="text/javascript" to <script>s 2023-11-21 01:12:07 +00:00			`<script type="text/javascript" src="bn.js"></script>`
			`<script type="text/javascript" src="nano-ethereum-signer-mod.js"></script>`
implement a proper flag encoder tool as an HTML+JS app 2023-08-20 01:20:23 +00:00			`</head>`

			`<body>`

add some field value length limits 2024-04-05 00:50:03 +00:00			<label for="inp-contestant-address">contestant's address:</label> <input id="inp-contestant-address" type="text" size="42" maxlength="42" pattern="0x[0-9a-fA-F]{40}" required placeholder="0x0000000000000000000000000000000000000000" autocomplete="cryptocurrency address" title="The cryptocurrency address of the contestant who is submitting the flag. It will be used as the message that is signed using an ECDSA signature scheme. It is incorporated to prevent submission forgery and theft. The resulting signature will be accepted by the CCTF smart-contract from only this address."/><br/>
			<label for="inp-flag">flag:</label> <input id="inp-flag" type="text" size="48" pattern="CCTF\{[ -~]*\}" required placeholder="CCTF{…}" autocomplete="flag" title="The flag for the challenge in question: a piece of data that can be found through solving the problem. It can be an outstanding character sequence of the form CCTF{…} that can be stumbled upon; otherwise its location/calculation (e.g. the deciphered message) and its formatting (e.g. hexadecimal) are precisely specified, and formatting always includes enclosing by CCTF{…}. The flag will be used as the secret key for signing using an ECDSA signature scheme." accesskey="f"/> <label for="outp-obscured-flag">⇒ obscured flag: </label><input id="outp-obscured-flag" type="text" size="42" maxlength="42" readonly title="The obscured flag: data to allow zero-knowledge verification of knowledge of the flag. It is the elliptic-curve public key related to the flag as the private key. It is the thing to be loaded into the CCTF smart-contract for the respective challenge."/><br />
			`<label for="outp-signature">⇒ signature: </label><input id="outp-signature" type="text" size="132" maxlength="132" readonly title="The signature: a zero-knowledge proof of knowledge of the flag, bound to the given address. It's an ECDSA signature of the address as the message (hash) with the flag as the key. It is to be passed to the CCTF smart-contract's flag submission function."/><!--<br />`
			`<label for="inp-contract-address">CCTF smart-contract address:</label> <input id="inp-contract-address" type="text" size="42" maxlength="42" pattern="0x[0-9a-fA-F]{40}" placeholder="0x0000000000000000000000000000000000000000"/><br/>`
implement a proper flag encoder tool as an HTML+JS app 2023-08-20 01:20:23 +00:00			`<label for="inp-contest-id">contest ID:</label> <input id="inp-contest-id" type="text" size="66" pattern="0x[0-9a-fA-F]+\|[0-9]+" placeholder="0x0000000000000000000000000000000000000000000000000000000000000000"/><br/>`
			`<label for="inp-challenge-id">challenge ID:</label> <input id="inp-challenge-id" type="integer" size="4" placeholder="0" accesskey="c"/>-->`

add type="text/javascript" to <script>s 2023-11-21 01:12:07 +00:00			`<script type="text/javascript">`
implement a proper flag encoder tool as an HTML+JS app 2023-08-20 01:20:23 +00:00			`var inpContestantAddress = document.querySelector("#inp-contestant-address");`
			`var inpFlag = document.querySelector("#inp-flag");`
			`var outpObscuredFlag = document.querySelector("#outp-obscured-flag");`
			`var outpSignature = document.querySelector("#outp-signature");`
properly handle the case where the (flag-derived) key is invalid (e.g., namely, unpopulated field) this practically rewrites the JavaScript code in the index.html file now the tool works without manual intervention 2023-11-22 19:10:27 +00:00			`var secp256k1n = new BN('115792089237316195423570985008687907852837564279074904382605163141518161494337', 10);`
implement a proper flag encoder tool as an HTML+JS app 2023-08-20 01:20:23 +00:00
properly handle the case where the (flag-derived) key is invalid (e.g., namely, unpopulated field) this practically rewrites the JavaScript code in the index.html file now the tool works without manual intervention 2023-11-22 19:10:27 +00:00			`function getPrivateKey() {`
			`var s = inpFlag.value;`
			`var h = "0x";`
ensure that the flag field is formatted as CCTF{...}, otherwise treat it as invalid 2024-04-04 00:16:55 +00:00			`if (s.slice(0, 5) !== "CCTF{" \|\| s.slice(-1) !== "}")`
			`return null;`
properly handle the case where the (flag-derived) key is invalid (e.g., namely, unpopulated field) this practically rewrites the JavaScript code in the index.html file now the tool works without manual intervention 2023-11-22 19:10:27 +00:00			`for (i in s) {`
			`var c = s.charCodeAt(i);`
allow only printable ASCII characters in flag strings 2024-04-04 00:34:13 +00:00			`if (c < 32 \|\| c > 126)`
			`return null;`
properly handle the case where the (flag-derived) key is invalid (e.g., namely, unpopulated field) this practically rewrites the JavaScript code in the index.html file now the tool works without manual intervention 2023-11-22 19:10:27 +00:00			`h += c.toString(16).padStart(2, "0");`
implement a proper flag encoder tool as an HTML+JS app 2023-08-20 01:20:23 +00:00			`}`
use "1 + (h mod (n - 1))" instead of "mod n" to cast a hash to a private key a private key must be in range [1, n - 1] this change neatly eliminates the scenario where the private key value ends up being 0, though it was extremely unlikely to occur in the first place (and could not even be easily forced) this changes the encoding -- players need to use the same encoding for submissions as the one used to post challenges 2024-04-04 23:40:07 +00:00			`return "0x" + new BN(keccak256(h).slice(2), 16).mod(secp256k1n.sub(new BN(1))).add(new BN(1)).toString(16).padStart(64, 0);`
implement a proper flag encoder tool as an HTML+JS app 2023-08-20 01:20:23 +00:00			`}`
properly handle the case where the (flag-derived) key is invalid (e.g., namely, unpopulated field) this practically rewrites the JavaScript code in the index.html file now the tool works without manual intervention 2023-11-22 19:10:27 +00:00
			`function updateOutputValues(ev) {`
			`var k = getPrivateKey();`
			`if (k === null) {`
			`outpObscuredFlag.value = "";`
implement a proper flag encoder tool as an HTML+JS app 2023-08-20 01:20:23 +00:00			`outpSignature.value = "";`
properly handle the case where the (flag-derived) key is invalid (e.g., namely, unpopulated field) this practically rewrites the JavaScript code in the index.html file now the tool works without manual intervention 2023-11-22 19:10:27 +00:00			`} else {`
			`outpObscuredFlag.value = addressFromKey(k);`
			`var m = inpContestantAddress.value;`
test the contestant address field for validity 2024-04-05 00:26:00 +00:00			`if (!/^0x[0-9a-fA-F]{40}$/.test(m)) {`
properly handle the case where the (flag-derived) key is invalid (e.g., namely, unpopulated field) this practically rewrites the JavaScript code in the index.html file now the tool works without manual intervention 2023-11-22 19:10:27 +00:00			`outpSignature.value = "";`
			`} else {`
			`outpSignature.value = signMessage(m, k);`
			`}`
implement a proper flag encoder tool as an HTML+JS app 2023-08-20 01:20:23 +00:00			`}`
			`}`

properly handle the case where the (flag-derived) key is invalid (e.g., namely, unpopulated field) this practically rewrites the JavaScript code in the index.html file now the tool works without manual intervention 2023-11-22 19:10:27 +00:00			`inpContestantAddress.oninput = updateOutputValues;`
			`inpFlag.oninput = updateOutputValues;`
implement a proper flag encoder tool as an HTML+JS app 2023-08-20 01:20:23 +00:00
properly handle the case where the (flag-derived) key is invalid (e.g., namely, unpopulated field) this practically rewrites the JavaScript code in the index.html file now the tool works without manual intervention 2023-11-22 19:10:27 +00:00			`updateOutputValues();`
implement a proper flag encoder tool as an HTML+JS app 2023-08-20 01:20:23 +00:00			`</script>`

			`</body>`
			`</html>`