add basic daily answer encryption

1 files changed, 52 insertions, 0 deletions

diff --git a/src/helpers/fetchSolution.ts b/src/helpers/fetchSolution.ts
new file mode 100644
index 0000000..b43722a
--- /dev/null
+++ b/src/helpers/fetchSolution.ts
@@ -0,0 +1,52 @@
+import { Song } from "../types/song";
+
+const SALT = process.env.HEARDLE_SALT ?? 'changeme';
+const API_URL = process.env.HEARDLE_API_URL ?? 'http://localhost:3001';
+
+function hexToBytes(hex: string): Uint8Array {
+  const bytes = new Uint8Array(hex.length / 2);
+  for (let i = 0; i < hex.length; i += 2) {
+    bytes[i / 2] = parseInt(hex.slice(i, i + 2), 16);
+  }
+  return bytes;
+}
+
+
+async function getDailyKey(): Promise<CryptoKey> {
+  const enc = new TextEncoder();
+  const date = new Date().toISOString().split('T')[0];
+  const keyMaterial = await crypto.subtle.importKey(
+    'raw',
+    enc.encode(date),
+    'PBKDF2',
+    false,
+    ['deriveKey'],
+  );
+  return crypto.subtle.deriveKey(
+    { name: 'PBKDF2', salt: enc.encode(SALT), iterations: 100_000, hash: 'SHA-256' },
+    keyMaterial,
+    { name: 'AES-GCM', length: 256 },
+    false,
+    ['decrypt'],
+  );
+}
+
+export async function getDailySolution(): Promise<Song> {
+  const solutionData = await fetch(`${API_URL}/today`);
+  if (!solutionData.ok) {
+    throw new Error(`Failed to fetch solution: ${solutionData.statusText}`);
+  }
+  const { iv, tag, data } = await solutionData.json();
+  const key = await getDailyKey();
+  const ciphertext = hexToBytes(data);
+  const authTag = hexToBytes(tag);
+  const combined = new Uint8Array(ciphertext.length + authTag.length);
+  combined.set(ciphertext);
+  combined.set(authTag, ciphertext.length);
+  const decrypted = await crypto.subtle.decrypt(
+    { name: 'AES-GCM', iv: hexToBytes(iv) },
+    key,
+    combined,
+  );
+  return JSON.parse(new TextDecoder().decode(decrypted)) as Song;
+}