1 files changed, 98 insertions, 0 deletions
diff --git a/chall/index.js b/chall/index.js
new file mode 100644
index 0000000..5c380bf
--- /dev/null
+++ b/chall/index.js
@@ -0,0 +1,98 @@
+const { noise } = require("./perlin.js");
+const sharp = require("sharp");
+const crypto = require("node:crypto");
+const readline = require("node:readline").promises;
+
+const FLAG = process.env.FLAG ?? console.log("No flag") ?? process.exit(1);
+const WIDTH = 256;
+const HEIGHT = 256;
+
+console.log(
+  `   _   _       _             ____                           _
+  | \\ | | ___ (_)___  ___   / ___| ___ _ __   ___ _ __ __ _| |_ ___  _ __
+  |  \\| |/ _ \\| / __|/ _ \\ | |  _ / _ \\ '_ \\ / _ \\ '__/ _\` | __/ _ \\| '__|
+  | |\\  | (_) | \\__ \\  __/ | |_| |  __/ | | |  __/ | | (_| | || (_) | |
+  |_| \\_|\\___/|_|___/\\___|  \\____|\\___|_| |_|\\___|_|  \\__,_|\\__\\___/|_|
+  `
+);
+
+console.log(`Flag length: ${FLAG.length}`);
+console.log(`Image width: ${WIDTH}`);
+console.log(`Image height: ${HEIGHT}`);
+
+const paddedFlag = [
+  ...crypto.randomBytes(8), // random prefix
+  ...Buffer.from(FLAG),
+  ...crypto.randomBytes(8), // random suffix
+];
+
+// bytes_to_long
+let flagInt = 0n;
+for (const b of Buffer.from(paddedFlag)) {
+  flagInt = (flagInt << 8n) | BigInt(b);
+}
+
+const generateNoise = async (scaleX, scaleY) => {
+  const div = (x, y) => {
+    const p = 4;
+    return Number(BigInt.asUintN(32 + p, (x * BigInt(1 << p)) / y)) / (1 << p);
+  };
+
+  const offsetX = div(flagInt, scaleX);
+  const offsetY = div(flagInt, scaleY);
+
+  noise.seed(crypto.randomInt(65536));
+  const colors = [];
+  for (let y = 0; y < HEIGHT; y++) {
+    for (let x = 0; x < WIDTH; x++) {
+      let v = noise.perlin2(offsetX + x * 0.05, offsetY + y * 0.05);
+      v = (v + 1.0) * 0.5; // [-1, 1] -> [0, 1]
+      colors.push((v * 256) | 0);
+    }
+  }
+
+  const image = await sharp(Uint8Array.from(colors), {
+    raw: {
+      width: WIDTH,
+      height: HEIGHT,
+      channels: 1,
+    },
+  })
+    .webp({ lossless: true })
+    .toBuffer();
+  return image;
+};
+
+const main = async () => {
+  const rl = readline.createInterface({
+    input: process.stdin,
+    output: process.stdout,
+    terminal: false,
+  });
+
+  const toBigInt = (value) => {
+    if (value.length > 100) {
+      console.log(`Invalid value: ${value}`);
+      process.exit(1);
+    }
+    const result = BigInt(value);
+    if (result <= 0n) {
+      console.log(`Invalid value: ${value}`);
+      process.exit(1);
+    }
+    return result;
+  };
+
+  const query = async () => {
+    const scaleX = toBigInt(await rl.question("Scale x: "));
+    const scaleY = toBigInt(await rl.question("Scale y: "));
+
+    const image = await generateNoise(scaleX, scaleY);
+    console.log(image.toString("base64"));
+  };
+  await query();
+
+  rl.close();
+};
+
+main();