1 files changed, 125 insertions, 0 deletions
diff --git a/tmpl.go b/tmpl.go
new file mode 100644
index 0000000..737e9c4
--- /dev/null
+++ b/tmpl.go
@@ -0,0 +1,125 @@
+package main
+
+import (
+	"html"
+	"log"
+	"text/template"
+)
+
+var tmpl *template.Template
+
+func init() {
+	var err error
+	tmpl, err = template.New("powxy").Parse(`
+<!DOCTYPE html>
+<html>
+<head>
+<title>Proof of Work Challenge</title>
+</head>
+<body>
+<h1>Proof of Work Challenge</h1>
+<p>This site is protected by <a href="https://forge.lindenii.runxiyu.org/powxy/:/repos/powxy/">Powxy</a>.</p>
+<p>You must complete this proof of work challenge before you could access this site.</p>
+{{- if .Message }}
+<p><strong>{{ .Message }}</strong></p>
+{{- end }}
+<p>Select an nonce shorter than or equal to 32 bytes, such that when it is appended to the decoded form of the following base64 string, and a SHA-256 hash is taken as a whole, the first {{ .NeedBits }} bits of the SHA-256 hash are zeros. Within one octet, higher bits are considered to be in front of lower bits.</p>
+<p>{{ .UnsignedTokenBase64 }}</p>
+<form method="POST">
+<p>
+Encode your selected nonce in base64 and submit it below:
+</p>
+<input name="powxy" type="text" />
+<input type="submit" value="Submit" />
+</form>
+<br />
+<details>
+<summary>Program to solve this</summary>
+<pre>` + html.EscapeString(solverProgram) + `</pre>
+</details>
+<p id="solver_status"></p>
+</body>
+<script>
+document.addEventListener("DOMContentLoaded", function() {
+	let challenge_b64 = "{{.UnsignedTokenBase64}}";
+	let difficulty = {{.NeedBits}};
+	let form = document.querySelector("form");
+	let field = form.querySelector("input[name='powxy']");
+	let status_el = document.getElementById("solver_status");
+
+	if (!window.crypto || !window.crypto.subtle) {
+		status_el.textContent = "SubtleCrypto not available. You must solve the challenge externally.";
+		return;
+	}
+	status_el.textContent = "SubtleCrypto detected. Attempting to solve in JS...";
+
+	let solver_active = true;
+	form.addEventListener("submit", function() {
+		solver_active = false;
+	});
+
+	async function solve_pow() {
+		let token_bytes = Uint8Array.from(
+			atob(challenge_b64),
+			ch => ch.charCodeAt(0)
+		);
+
+		let nonce = 0n;
+		let buf = new ArrayBuffer(8);
+		let view = new DataView(buf);
+
+		while (solver_active) {
+			view.setBigUint64(0, nonce, true);
+
+			let candidate = new Uint8Array(token_bytes.length + 8);
+			candidate.set(token_bytes, 0);
+			candidate.set(new Uint8Array(buf), token_bytes.length);
+
+			let digest_buffer = await crypto.subtle.digest("SHA-256", candidate);
+			let digest = new Uint8Array(digest_buffer);
+
+			if (has_leading_zero_bits(digest, difficulty)) {
+				let nonce_str = String.fromCharCode(...new Uint8Array(buf));
+				field.value = btoa(nonce_str);
+
+				status_el.textContent = "Solution found. Submitting...";
+				form.submit();
+				return;
+			}
+
+			nonce++;
+
+			// Update status every 256 tries
+			if ((nonce & 0x00FFn) === 0n) {
+				status_el.textContent = "Tried " + nonce + " candidates so far...";
+				await new Promise(r => setTimeout(r, 0));
+			}
+		}
+	}
+
+	function has_leading_zero_bits(digest, bits) {
+		let full_bytes = bits >>> 3;
+		for (let i = 0; i < full_bytes; i++) {
+			if (digest[i] !== 0) {
+				return false;
+			}
+		}
+		let remainder = bits & 7;
+		if (remainder !== 0) {
+			let mask = 0xFF << (8 - remainder);
+			if ((digest[full_bytes] & mask) !== 0) {
+				return false;
+			}
+		}
+		return true;
+	}
+
+	solve_pow();
+});
+</script>
+</html>
+`)
+	if err != nil {
+		log.Fatal(err)
+	}
+}