8 files changed, 578 insertions, 166 deletions

diff --git a/package.json b/package.json
index 7b07c3e..ccd7ad9 100644
--- a/package.json
+++ b/package.json
@@ -14,6 +14,7 @@
     "cors": "^2.8.6",
     "dotenv": "^17.4.2",
     "express": "^5.2.1",
+    "express-rate-limit": "^8.5.2",
     "lodash": "^4.18.1",
     "prop-types": "^15.8.1",
     "react": "^19.2.7",
diff --git a/playlist_generator/generate_daily.py b/playlist_generator/generate_daily.py
index aba73b0..1e6e39e 100644
--- a/playlist_generator/generate_daily.py
+++ b/playlist_generator/generate_daily.py
@@ -15,15 +15,21 @@ ACCESS_KEY = os.getenv("R2_ACCESS_KEY")
 SECRET_KEY = os.getenv("R2_SECRET_KEY")
 BUCKET = os.getenv("R2_BUCKET")
 API_URL = os.getenv("API_URL")
-OBFUSCATION_KEY = os.getenv("OBFUSCATION_KEY")
+HEARDLE_SALT = (
+    os.getenv("VITE_HEARDLE_SALT")
+    or os.getenv("OBFUSCATION_KEY")
+)
 
 
 def xor_buffer(data: bytes, key: bytes) -> bytes:
     return bytes(b ^ key[i % len(key)] for i, b in enumerate(data))
 
-def get_obfuscation_key() -> bytes:
-    date = datetime.now(timezone.utc).strftime("%Y-%m-%d")
-    return (OBFUSCATION_KEY + date).encode("utf-8")
+def get_obfuscation_key(date: str) -> bytes:
+    if not HEARDLE_SALT:
+        raise ValueError(
+            "Missing HEARDLE salt. Set VITE_HEARDLE_SALT (preferred) or OBFUSCATION_KEY."
+        )
+    return (HEARDLE_SALT + date).encode("utf-8")
 
 def delete_file(file_path):
     if os.path.exists(file_path):
@@ -31,18 +37,25 @@ def delete_file(file_path):
         return True
     return False
 
-def decode_data(hex_data: str):
+def decode_data(hex_data: str, date: str):
     encrypted = bytes.fromhex(hex_data)
-    key = get_obfuscation_key()
+    key = get_obfuscation_key(date)
     decrypted = xor_buffer(encrypted, key)
     return json.loads(decrypted.decode("utf-8"))
 
 
 def fetch_daily() -> dict:
+    if not API_URL:
+        raise ValueError("Missing API_URL in environment.")
+
     url = f"{API_URL}/today"
-    response = requests.get(url)
+    response = requests.get(url, timeout=15)
     response.raise_for_status()
-    return response.json()
+    payload = response.json()
+    if "date" not in payload or "data" not in payload:
+        raise ValueError(f"Unexpected /today response shape: {payload}")
+
+    return payload
 
 
 def download_random_segment_mp3(youtube_id: str, output_file="today.mp3") -> str:
@@ -116,11 +129,11 @@ def main():
         else:
             new_data = True
         daily_data = fetch_daily()
-    data = decode_data(daily_data["data"])
+    data = decode_data(daily_data["data"], daily_data["date"])
     print(data)
     youtube_id = data["youtubeId"]
     clip_path = download_random_segment_mp3(youtube_id)
-    date = datetime.now(timezone.utc).strftime("%Y-%m-%d")
+    date = daily_data["date"]
     upload_to_r2(clip_path, f"kheardle/{date}.mp3")
     delete_file("today.mp3")
     write_json("save.json", daily_data)
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index 828f20b..c30d2fb 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -43,6 +43,9 @@ dependencies:
   express:
     specifier: ^5.2.1
     version: 5.2.1
+  express-rate-limit:
+    specifier: ^8.5.2
+    version: 8.5.2(express@5.2.1)
   lodash:
     specifier: ^4.18.1
     version: 4.18.1
@@ -1816,6 +1819,16 @@ packages:
       jest-util: 30.4.1
     dev: false
 
+  /express-rate-limit@8.5.2(express@5.2.1):
+    resolution: {integrity: sha512-5Kb34ipNX694DH48vN9irak1Qx30nb0PLYHXfJgw4YEjiC3ZEmZJhwOp+VfiCYwFzvFTdB9QkArYS5kXa2cx2A==}
+    engines: {node: '>= 16'}
+    peerDependencies:
+      express: '>= 4.11'
+    dependencies:
+      express: 5.2.1
+      ip-address: 10.2.0
+    dev: false
+
   /express@5.2.1:
     resolution: {integrity: sha512-hIS4idWWai69NezIdRt2xFVofaF4j+6INOpJlVOLDO8zXGpUVEVzIYk12UUi2JzjEzWL3IOAxcTubgz9Po0yXw==}
     engines: {node: '>= 18'}
@@ -2071,6 +2084,11 @@ packages:
     resolution: {integrity: sha512-k/vGaX4/Yla3WzyMCvTQOXYeIHvqOKtnqBduzTHpzpQZzAskKMhZ2K+EnBiSM9zGSoIFeMpXKxa4dYeZIQqewQ==}
     dev: false
 
+  /ip-address@10.2.0:
+    resolution: {integrity: sha512-/+S6j4E9AHvW9SWMSEY9Xfy66O5PWvVEJ08O0y5JGyEKQpojb0K0GKpz/v5HJ/G0vi3D2sjGK78119oXZeE0qA==}
+    engines: {node: '>= 12'}
+    dev: false
+
   /ipaddr.js@1.9.1:
     resolution: {integrity: sha512-0KI/607xoxSToH7GjN1FfSbLoU0+btTicjsQSWQlh/hZykN8KpmMf7uYwPW3R+akZ6R/w18ZlXSHBYXiYUPO3g==}
     engines: {node: '>= 0.10'}
diff --git a/server/index.ts b/server/index.ts
index c9cc6b4..3737105 100644
--- a/server/index.ts
+++ b/server/index.ts
@@ -1,9 +1,10 @@
-import express from 'express';
-import { existsSync, mkdirSync, readFileSync, writeFileSync } from 'fs';
-import path from 'path';
-import { songs } from './data/songs';
-import cors from 'cors';
-import dotenv from 'dotenv';
+import express from "express";
+import { createHmac, timingSafeEqual } from "crypto";
+import { songs } from "./data/songs";
+import cors from "cors";
+import dotenv from "dotenv";
+import rateLimit from "express-rate-limit";
+
 dotenv.config();
 
 const app = express();
@@ -11,13 +12,27 @@ app.use(cors());
 app.use(express.json());
 
 const SERVER_PORT = process.env.SERVER_PORT || 3001;
-const SALT = process.env.VITE_HEARDLE_SALT ?? 'changeme';
-const DAILY_SONGS_FILE = path.resolve(
-  process.env.DAILY_SONGS_FILE ?? 'server/data/daily-songs.json',
-);
+const SALT = process.env.VITE_HEARDLE_SALT ?? "changeme";
+const SIGNING_SECRET = process.env.HEARDLE_SIGNING_SECRET ?? SALT;
 
 type Song = (typeof songs)[number];
-type DailySongs = Record<string, Song>;
+
+type GuessResult = "Correct" | "PartiallyCorrect" | "Incorrect" | "Skipped";
+
+type GuessEntry = {
+  song?: {
+    artist: string;
+    name: string;
+  };
+  state: GuessResult;
+};
+
+type SignedState = {
+  date: string;
+  currentTry: number;
+  didGuess: boolean;
+  guesses: GuessEntry[];
+};
 
 function getObfuscationKey(date = getUtcDate()): Buffer {
   return Buffer.from(SALT + date);
@@ -34,6 +49,7 @@ function xorBuffer(data: Buffer, key: Buffer): Buffer {
 function getUtcDate(): string {
   return new Date().toISOString().slice(0, 10);
 }
+
 function hashString(str: string): number {
   let hash = 0;
   for (let i = 0; i < str.length; i++) {
@@ -42,60 +58,277 @@ function hashString(str: string): number {
   return hash;
 }
 
-function readDailySongs(): DailySongs {
-  if (!existsSync(DAILY_SONGS_FILE)) {
-    return {};
+function getDailySong(date: string): Song {
+  const seed = hashString(date);
+  const index = seed % songs.length;
+  return songs[index];
+}
+
+function signValue(prefix: string, value: string): string {
+  return createHmac("sha256", SIGNING_SECRET)
+    .update(`${prefix}:${value}`)
+    .digest("hex");
+}
+
+function safeEqualHex(a: string, b: string): boolean {
+  try {
+    const left = Buffer.from(a, "hex");
+    const right = Buffer.from(b, "hex");
+    if (left.length !== right.length) return false;
+    return timingSafeEqual(left, right);
+  } catch {
+    return false;
   }
+}
 
-  return JSON.parse(readFileSync(DAILY_SONGS_FILE, 'utf8')) as DailySongs;
+function buildSessionToken(date: string): string {
+  const payload = Buffer.from(JSON.stringify({ date }), "utf8").toString("base64url");
+  const sig = signValue("session", payload);
+  return `${payload}.${sig}`;
 }
 
-function writeDailySongs(dailySongs: DailySongs): void {
-  mkdirSync(path.dirname(DAILY_SONGS_FILE), { recursive: true });
-  writeFileSync(DAILY_SONGS_FILE, JSON.stringify(dailySongs, null, 2));
+function verifySessionToken(token: unknown, expectedDate: string): boolean {
+  if (typeof token !== "string") return false;
+  const [payload, sig] = token.split(".");
+  if (!payload || !sig) return false;
+
+  const expectedSig = signValue("session", payload);
+  if (!safeEqualHex(sig, expectedSig)) return false;
+
+  try {
+    const decoded = JSON.parse(Buffer.from(payload, "base64url").toString("utf8")) as {
+      date?: unknown;
+    };
+
+    return typeof decoded.date === "string" && decoded.date === expectedDate;
+  } catch {
+    return false;
+  }
 }
 
-function getDailySong(date: string): Song {
-  const dailySongs = readDailySongs();
-  const savedSong = dailySongs[date];
+function normalizeGuessEntry(entry: unknown): GuessEntry | null {
+  if (!entry || typeof entry !== "object" || Array.isArray(entry)) return null;
 
-  if (savedSong) {
-    return savedSong;
+  const maybeState = (entry as { state?: unknown }).state;
+  if (
+    maybeState !== "Correct" &&
+    maybeState !== "PartiallyCorrect" &&
+    maybeState !== "Incorrect" &&
+    maybeState !== "Skipped"
+  ) {
+    return null;
   }
 
-  const seed = hashString(date);
-  const index = seed % songs.length;
-  const song = songs[index];
-  dailySongs[date] = song;
-  writeDailySongs(dailySongs);
-  return song;
+  const maybeSong = (entry as { song?: unknown }).song;
+
+  if (maybeState === "Skipped") {
+    return { state: "Skipped" };
+  }
+
+  if (!maybeSong || typeof maybeSong !== "object" || Array.isArray(maybeSong)) {
+    return null;
+  }
+
+  const artist = (maybeSong as { artist?: unknown }).artist;
+  const name = (maybeSong as { name?: unknown }).name;
+
+  if (typeof artist !== "string" || typeof name !== "string") {
+    return null;
+  }
+
+  return {
+    song: { artist, name },
+    state: maybeState,
+  };
 }
 
-app.get('/today', (_req, res) => {
+function normalizeSignedState(input: unknown): SignedState | null {
+  if (!input || typeof input !== "object" || Array.isArray(input)) return null;
+
+  const date = (input as { date?: unknown }).date;
+  const currentTryRaw = (input as { currentTry?: unknown }).currentTry;
+  const didGuessRaw = (input as { didGuess?: unknown }).didGuess;
+  const guessesRaw = (input as { guesses?: unknown }).guesses;
+
+  if (typeof date !== "string") return null;
+  if (!Array.isArray(guessesRaw)) return null;
+  if (typeof currentTryRaw !== "number" || !Number.isFinite(currentTryRaw)) return null;
+
+  const currentTry = Math.floor(currentTryRaw);
+  if (currentTry < 0 || currentTry > 6) return null;
+
+  const guesses: GuessEntry[] = [];
+  for (const entry of guessesRaw) {
+    const normalized = normalizeGuessEntry(entry);
+    if (!normalized) return null;
+    guesses.push(normalized);
+  }
+
+  if (guesses.length > 6) return null;
+  if (guesses.length !== currentTry) return null;
+
+  const didGuess = !!didGuessRaw;
+  if (didGuess && !guesses.some((guess) => guess.state === "Correct")) {
+    return null;
+  }
+
+  return {
+    date,
+    currentTry,
+    didGuess,
+    guesses,
+  };
+}
+
+function canonicalState(state: SignedState): string {
+  return JSON.stringify({
+    date: state.date,
+    currentTry: state.currentTry,
+    didGuess: state.didGuess,
+    guesses: state.guesses.map((guess) => ({
+      state: guess.state,
+      song: guess.song
+        ? {
+            artist: guess.song.artist,
+            name: guess.song.name,
+          }
+        : null,
+    })),
+  });
+}
+
+function signState(state: SignedState): string {
+  return signValue("state", canonicalState(state));
+}
+
+function verifyStateSignature(state: SignedState, sig: unknown): boolean {
+  if (typeof sig !== "string") return false;
+  const expectedSig = signState(state);
+  return safeEqualHex(sig, expectedSig);
+}
+
+const guessLimiter = rateLimit({
+  windowMs: 60 * 1000,
+  limit: 30,
+  standardHeaders: true,
+  legacyHeaders: false,
+  message: { error: "Too many requests. Please slow down." },
+});
+
+app.get("/today", (_req, res) => {
   const date = getUtcDate();
   const song = getDailySong(date);
   const obfuscationKey = getObfuscationKey(date);
   const songJson = JSON.stringify(song);
-  const obfuscatedData = xorBuffer(Buffer.from(songJson, 'utf8'), obfuscationKey);
+  const obfuscatedData = xorBuffer(Buffer.from(songJson, "utf8"), obfuscationKey);
+
+  const initialState: SignedState = {
+    date,
+    currentTry: 0,
+    didGuess: false,
+    guesses: [],
+  };
+
   res.json({
     date,
-    data: obfuscatedData.toString('hex'),
+    data: obfuscatedData.toString("hex"),
+    sessionToken: buildSessionToken(date),
+    initialSig: signState(initialState),
+  });
+});
+
+app.post("/guess", guessLimiter, (req, res) => {
+  const today = getUtcDate();
+  const body = req.body as {
+    sessionToken?: unknown;
+    state?: unknown;
+    sig?: unknown;
+    guess?: unknown;
+  };
+
+  if (!verifySessionToken(body.sessionToken, today)) {
+    res.status(401).json({ error: "Invalid session token." });
+    return;
+  }
+
+  const state = normalizeSignedState(body.state);
+  if (!state) {
+    res.status(400).json({ error: "Invalid state payload." });
+    return;
+  }
+
+  if (state.date !== today) {
+    res.status(409).json({ error: "State date is not valid for today." });
+    return;
+  }
+
+  if (!verifyStateSignature(state, body.sig)) {
+    res.status(403).json({ error: "State signature mismatch." });
+    return;
+  }
+
+  if (state.didGuess || state.currentTry >= 6) {
+    res.status(409).json({ error: "Round already finished." });
+    return;
+  }
+
+  let nextGuess: GuessEntry;
+  const guess = body.guess as { artist?: unknown; name?: unknown } | null | undefined;
+
+  if (guess == null) {
+    nextGuess = {
+      state: "Skipped",
+    };
+  } else if (typeof guess.artist === "string" && typeof guess.name === "string") {
+    const solution = getDailySong(today);
+
+    if (guess.artist === solution.artist && guess.name === solution.name) {
+      nextGuess = {
+        song: { artist: guess.artist, name: guess.name },
+        state: "Correct",
+      };
+    } else if (guess.artist === solution.artist) {
+      nextGuess = {
+        song: { artist: guess.artist, name: guess.name },
+        state: "PartiallyCorrect",
+      };
+    } else {
+      nextGuess = {
+        song: { artist: guess.artist, name: guess.name },
+        state: "Incorrect",
+      };
+    }
+  } else {
+    res.status(400).json({ error: "Invalid guess payload." });
+    return;
+  }
+
+  const nextState: SignedState = {
+    date: state.date,
+    currentTry: Math.min(6, state.currentTry + 1),
+    didGuess: state.didGuess || nextGuess.state === "Correct",
+    guesses: [...state.guesses, nextGuess],
+  };
+
+  res.json({
+    state: nextState,
+    sig: signState(nextState),
+    guessState: nextGuess.state,
   });
 });
 
-app.get('/select', (_req, res) => {
+app.get("/select", (_req, res) => {
   const song = songs[Math.floor(Math.random() * songs.length)];
   const obfuscationKey = getObfuscationKey();
   const songJson = JSON.stringify(song);
-  const obfuscatedData = xorBuffer(Buffer.from(songJson, 'utf8'), obfuscationKey);
+  const obfuscatedData = xorBuffer(Buffer.from(songJson, "utf8"), obfuscationKey);
   res.json({
-    data: obfuscatedData.toString('hex'),
+    data: obfuscatedData.toString("hex"),
   });
 });
 
-app.get('/songs', (_req, res) => {
+app.get("/songs", (_req, res) => {
   res.json(songs.map(({ artist, name }) => ({ artist, name })));
 });
 
-
 app.listen(SERVER_PORT, () => console.log(`Server running on :${SERVER_PORT}`));
diff --git a/src/helpers/fetchSolution.ts b/src/helpers/fetchSolution.ts
index e3010fe..d877d8f 100644
--- a/src/helpers/fetchSolution.ts
+++ b/src/helpers/fetchSolution.ts
@@ -1,17 +1,17 @@
 import { Song } from "../types/song";
+import { GuessState, GuessType } from "../types/guess";
 
-const SALT = import.meta.env.VITE_HEARDLE_SALT ?? 'changeme';
-const API_URL = import.meta.env.VITE_HEARDLE_API_URL ?? 'http://localhost:3001';
+const SALT = import.meta.env.VITE_HEARDLE_SALT ?? "changeme";
+const API_URL = import.meta.env.VITE_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;
+  return bytes;
 }
 
-
 function xor(data: Uint8Array, key: Uint8Array): Uint8Array {
   const output = new Uint8Array(data.length);
   for (let i = 0; i < data.length; i++) {
@@ -20,7 +20,7 @@ function xor(data: Uint8Array, key: Uint8Array): Uint8Array {
   return output;
 }
 
-function getObfuscationKey(date = new Date().toISOString().split('T')[0]): Uint8Array {
+function getObfuscationKey(date = new Date().toISOString().split("T")[0]): Uint8Array {
   return new TextEncoder().encode(SALT + date);
 }
 
@@ -34,6 +34,33 @@ function decryptResponse(data: string, date?: string): Song {
 export interface DailySolution {
   date: string;
   song: Song;
+  sessionToken: string;
+  initialSig: string;
+}
+
+export interface DailyGameState {
+  date: string;
+  currentTry: number;
+  didGuess: boolean;
+  guesses: GuessType[];
+}
+
+interface SongGuessPayload {
+  artist: string;
+  name: string;
+}
+
+interface SubmitDailyGuessRequest {
+  sessionToken: string;
+  state: DailyGameState;
+  sig: string;
+  guess?: SongGuessPayload | null;
+}
+
+interface SubmitDailyGuessResponse {
+  state: DailyGameState;
+  sig: string;
+  guessState: GuessState;
 }
 
 export async function getDailySolution(): Promise<DailySolution> {
@@ -41,13 +68,33 @@ export async function getDailySolution(): Promise<DailySolution> {
   if (!solutionData.ok) {
     throw new Error(`Failed to fetch solution: ${solutionData.statusText}`);
   }
-  const { data, date } = await solutionData.json();
+  const { data, date, sessionToken, initialSig } = await solutionData.json();
   return {
     date,
+    sessionToken,
+    initialSig,
     song: decryptResponse(data, date),
   };
 }
 
+export async function submitDailyGuess(
+  payload: SubmitDailyGuessRequest
+): Promise<SubmitDailyGuessResponse> {
+  const response = await fetch(`${API_URL}/guess`, {
+    method: "POST",
+    headers: {
+      "Content-Type": "application/json",
+    },
+    body: JSON.stringify(payload),
+  });
+
+  if (!response.ok) {
+    throw new Error(`Failed to submit guess: ${response.statusText}`);
+  }
+
+  return (await response.json()) as SubmitDailyGuessResponse;
+}
+
 export async function getSelectSolution(): Promise<Song> {
   const solutionData = await fetch(`${API_URL}/select`);
   if (!solutionData.ok) {
diff --git a/src/hooks/useGameState.ts b/src/hooks/useGameState.ts
index 625dddf..f4b3763 100644
--- a/src/hooks/useGameState.ts
+++ b/src/hooks/useGameState.ts
@@ -1,21 +1,33 @@
 import React from "react";
-import _ from "lodash";
-
 import { Song } from "../types/song";
 import { GuessState, GuessType } from "../types/guess";
+import { DailyGameState, submitDailyGuess } from "../helpers/fetchSolution";
 
 interface UseGameStateOptions {
   solution: Song | null;
   persist: boolean;
+  sessionDate?: string;
+  sessionToken?: string;
+  initialSig?: string;
+}
+
+const STATE_VERSION = 2;
+
+interface PersistedStatsV2 extends DailyGameState {
+  version: number;
+  sig: string;
+  sessionToken: string;
 }
 
-interface PersistedStats {
-  solution: string;
+interface LegacyStatsV0 {
+  date: string;
   currentTry: number;
   didGuess: boolean;
   guesses: GuessType[];
 }
 
+type PersistedStats = PersistedStatsV2;
+
 const initialGuess: GuessType = {
   song: undefined,
   state: undefined,
@@ -29,174 +41,151 @@ const isAnsweredGuess = (guess: GuessType | undefined | null) =>
 
 const normalizeAnsweredGuesses = (guesses: unknown): GuessType[] => {
   if (!Array.isArray(guesses)) return [];
-  if (guesses.some((guess) => Array.isArray(guess))) return [];
-
+  if (guesses.some((g) => Array.isArray(g))) return [];
   return (guesses as GuessType[]).filter(isAnsweredGuess).slice(0, 6);
 };
 
-const SALT = import.meta.env.VITE_HEARDLE_SALT || "changeme";
-
-const getKey = (salt: string) => {
-  let key = 0;
-  for (let i = 0; i < salt.length; i++) {
-    key = (key + salt.charCodeAt(i)) % 256;
-  }
-  return key;
-};
-
-const KEY = getKey(SALT);
-
 function loadStats(): PersistedStats | null {
   try {
     const raw = localStorage.getItem("stats");
     if (!raw) return null;
 
     const parsed = JSON.parse(raw);
-
-    if (!parsed || Array.isArray(parsed) || typeof parsed !== "object") {
+    if (!parsed || typeof parsed !== "object" || Array.isArray(parsed)) {
       localStorage.removeItem("stats");
       return null;
     }
 
+    const isLegacyV0 =
+      !("version" in parsed) &&
+      "date" in parsed &&
+      "guesses" in parsed &&
+      !("sig" in parsed);
+
+    if (isLegacyV0) {
+      const legacy = parsed as LegacyStatsV0;
+
+      const upgraded: PersistedStats = {
+        version: STATE_VERSION,
+        date: legacy.date,
+        currentTry: Math.max(
+          0,
+          Math.min(6, Math.floor(legacy.currentTry || 0))
+        ),
+        didGuess: !!legacy.didGuess,
+        guesses: normalizeAnsweredGuesses(legacy.guesses),
+        sig: "",
+        sessionToken: "",
+      };
+
+      return upgraded;
+    }
+
     const currentTry =
       typeof parsed.currentTry === "number" && Number.isFinite(parsed.currentTry)
         ? Math.max(0, Math.min(6, Math.floor(parsed.currentTry)))
         : 0;
 
-    const normalized: PersistedStats = {
-      solution: typeof parsed.solution === "string" ? parsed.solution : "",
-      currentTry,
+    const normalizedGuesses = normalizeAnsweredGuesses(parsed.guesses);
+
+    return {
+      version: typeof parsed.version === "number" ? parsed.version : STATE_VERSION,
+      date: typeof parsed.date === "string" ? parsed.date : "",
+      currentTry: Math.min(currentTry, normalizedGuesses.length),
       didGuess: !!parsed.didGuess,
-      guesses: normalizeAnsweredGuesses(parsed.guesses),
+      guesses: normalizedGuesses,
+      sig: typeof parsed.sig === "string" ? parsed.sig : "",
+      sessionToken:
+        typeof parsed.sessionToken === "string" ? parsed.sessionToken : "",
     };
-
-    return normalized;
   } catch {
     localStorage.removeItem("stats");
     return null;
   }
 }
 
-const encodeSolution = (solution: Song) => {
-  const json = JSON.stringify(solution);
-
-  const xored = json
-    .split("")
-    .map((c) => String.fromCharCode(c.charCodeAt(0) ^ KEY))
-    .join("");
-
-  return btoa(xored);
-};
-
-const decodeSolution = (value: string): Song | null => {
-  try {
-    const decoded = atob(value);
-
-    const json = decoded
-      .split("")
-      .map((c) => String.fromCharCode(c.charCodeAt(0) ^ KEY))
-      .join("");
-
-    return JSON.parse(json);
-  } catch {
-    return null;
-  }
-};
-
-export function useGameState({ solution, persist }: UseGameStateOptions) {
+export function useGameState({
+  solution,
+  persist,
+  sessionDate,
+  sessionToken,
+  initialSig,
+}: UseGameStateOptions) {
   const [guesses, setGuesses] = React.useState<GuessType[]>(makeEmptyGuesses());
-
   const [currentTry, setCurrentTry] = React.useState(0);
   const [selectedSong, setSelectedSong] = React.useState<Song>();
   const [didGuess, setDidGuess] = React.useState(false);
+  const [isSubmitting, setIsSubmitting] = React.useState(false);
 
   const [stats, setStats] = React.useState<PersistedStats | null>(() =>
     loadStats()
   );
 
   const hydratedRef = React.useRef(false);
-  const skipNextStatsSyncRef = React.useRef(false);
 
   React.useEffect(() => {
-    if (!persist || !solution) return;
+    if (!persist) return;
     if (hydratedRef.current) return;
+    if (!sessionDate || !sessionToken || !initialSig) return;
 
-    skipNextStatsSyncRef.current = true;
-
-    const initialStats: PersistedStats = {
-      solution: encodeSolution(solution),
+    const baseStats: PersistedStats = {
+      version: STATE_VERSION,
+      date: sessionDate,
       currentTry: 0,
       didGuess: false,
       guesses: [],
+      sig: initialSig,
+      sessionToken,
     };
 
     if (!stats) {
-      setStats(initialStats);
+      setStats(baseStats);
+      setCurrentTry(0);
+      setGuesses(makeEmptyGuesses());
+      setDidGuess(false);
       hydratedRef.current = true;
       return;
     }
 
-    const decodedSolution = stats.solution
-      ? decodeSolution(stats.solution)
-      : null;
+    const sameSession =
+      stats.date === sessionDate &&
+      stats.sessionToken === sessionToken;
 
-    const sameGame = _.isEqual(solution, decodedSolution);
+    if (sameSession) {
+      const answered = normalizeAnsweredGuesses(stats.guesses);
+      const hydrated = makeEmptyGuesses();
 
-    if (sameGame) {
-      const answeredGuesses = normalizeAnsweredGuesses(stats.guesses);
-      const hydratedGuesses = makeEmptyGuesses();
+      answered.forEach((g, i) => (hydrated[i] = g));
 
-      answeredGuesses.forEach((guess, index) => {
-        hydratedGuesses[index] = guess;
-      });
-
-      const normalizedCurrentTry = Math.min(
-        answeredGuesses.length,
-        Math.max(0, stats.currentTry ?? 0)
+      const normalizedTry = Math.min(
+        answered.length,
+        Math.max(0, stats.currentTry)
       );
 
-      setCurrentTry(normalizedCurrentTry);
-      setGuesses(hydratedGuesses);
+      setCurrentTry(normalizedTry);
+      setGuesses(hydrated);
       setDidGuess(!!stats.didGuess);
+
       setStats({
         ...stats,
-        currentTry: normalizedCurrentTry,
-        guesses: answeredGuesses,
+        version: STATE_VERSION,
+        currentTry: normalizedTry,
+        guesses: answered,
       });
     } else {
-      setStats(initialStats);
+      setStats(baseStats);
       setCurrentTry(0);
       setGuesses(makeEmptyGuesses());
       setDidGuess(false);
     }
 
     hydratedRef.current = true;
-  }, [solution, persist]);
+  }, [persist, sessionDate, sessionToken, initialSig, stats]);
 
   React.useEffect(() => {
     if (!persist) return;
     if (!hydratedRef.current) return;
 
-    if (skipNextStatsSyncRef.current) {
-      skipNextStatsSyncRef.current = false;
-      return;
-    }
-
-    setStats((prev) => {
-      if (!prev) return prev;
-
-      return {
-        ...prev,
-        currentTry,
-        didGuess,
-        guesses: guesses.filter(isAnsweredGuess),
-      };
-    });
-  }, [guesses, currentTry, didGuess, persist]);
-
-  React.useEffect(() => {
-    if (!persist) return;
-    if (!hydratedRef.current) return;
     if (!stats) {
       localStorage.removeItem("stats");
       return;
@@ -205,9 +194,65 @@ export function useGameState({ solution, persist }: UseGameStateOptions) {
     localStorage.setItem("stats", JSON.stringify(stats));
   }, [stats, persist]);
 
-  const skip = React.useCallback(() => {
+  const applyServerState = React.useCallback(
+    (next: DailyGameState, sig: string) => {
+      if (!sessionToken) return;
+
+      const answered = normalizeAnsweredGuesses(next.guesses);
+      const hydrated = makeEmptyGuesses();
+
+      answered.forEach((g, i) => (hydrated[i] = g));
+
+      const normalizedTry = Math.min(
+        answered.length,
+        Math.max(0, next.currentTry)
+      );
+
+      setCurrentTry(normalizedTry);
+      setGuesses(hydrated);
+      setDidGuess(!!next.didGuess);
+      setSelectedSong(undefined);
+
+      setStats({
+        version: STATE_VERSION,
+        date: next.date,
+        currentTry: normalizedTry,
+        didGuess: !!next.didGuess,
+        guesses: answered,
+        sig,
+        sessionToken,
+      });
+    },
+    [sessionToken]
+  );
+
+  const skip = React.useCallback(async () => {
     if (didGuess || currentTry >= guesses.length) return;
 
+    if (persist && sessionDate && sessionToken) {
+      if (!stats?.sig || isSubmitting) return;
+
+      setIsSubmitting(true);
+      try {
+        const res = await submitDailyGuess({
+          sessionToken,
+          sig: stats.sig,
+          state: {
+            date: sessionDate,
+            currentTry,
+            didGuess,
+            guesses: guesses.filter(isAnsweredGuess),
+          },
+          guess: null,
+        });
+
+        applyServerState(res.state, res.sig);
+      } finally {
+        setIsSubmitting(false);
+      }
+      return;
+    }
+
     setGuesses((prev) => {
       const copy = [...prev];
       copy[currentTry] = {
@@ -218,12 +263,49 @@ export function useGameState({ solution, persist }: UseGameStateOptions) {
     });
 
     setCurrentTry((t) => t + 1);
-  }, [currentTry, didGuess, guesses.length]);
+  }, [
+    didGuess,
+    currentTry,
+    guesses,
+    persist,
+    sessionDate,
+    sessionToken,
+    stats,
+    isSubmitting,
+    applyServerState,
+  ]);
 
-  const guess = React.useCallback(() => {
+  const guess = React.useCallback(async () => {
     if (!selectedSong || !solution) return;
     if (didGuess || currentTry >= guesses.length) return;
 
+    if (persist && sessionDate && sessionToken) {
+      if (!stats?.sig || isSubmitting) return;
+
+      setIsSubmitting(true);
+      try {
+        const res = await submitDailyGuess({
+          sessionToken,
+          sig: stats.sig,
+          state: {
+            date: sessionDate,
+            currentTry,
+            didGuess,
+            guesses: guesses.filter(isAnsweredGuess),
+          },
+          guess: {
+            artist: selectedSong.artist,
+            name: selectedSong.name,
+          },
+        });
+
+        applyServerState(res.state, res.sig);
+      } finally {
+        setIsSubmitting(false);
+      }
+      return;
+    }
+
     let state = GuessState.Incorrect;
 
     if (
@@ -237,20 +319,27 @@ export function useGameState({ solution, persist }: UseGameStateOptions) {
 
     setGuesses((prev) => {
       const copy = [...prev];
-      copy[currentTry] = {
-        song: selectedSong,
-        state,
-      };
+      copy[currentTry] = { song: selectedSong, state };
       return copy;
     });
 
     setCurrentTry((t) => t + 1);
     setSelectedSong(undefined);
 
-    if (state === GuessState.Correct) {
-      setDidGuess(true);
-    }
-  }, [selectedSong, solution, currentTry, didGuess, guesses.length]);
+    if (state === GuessState.Correct) setDidGuess(true);
+  }, [
+    selectedSong,
+    solution,
+    currentTry,
+    didGuess,
+    guesses,
+    persist,
+    sessionDate,
+    sessionToken,
+    stats,
+    isSubmitting,
+    applyServerState,
+  ]);
 
   const reset = React.useCallback(() => {
     setGuesses(makeEmptyGuesses());
diff --git a/src/pages/DailyPage.tsx b/src/pages/DailyPage.tsx
index 24ac20c..d1482b1 100644
--- a/src/pages/DailyPage.tsx
+++ b/src/pages/DailyPage.tsx
@@ -69,7 +69,13 @@ export function DailyPage() {
     didGuess,
     skip,
     guess,
-  } = useGameState({ solution: todaysSolution?.song ?? null, persist: true });
+  } = useGameState({
+    solution: todaysSolution?.song ?? null,
+    persist: true,
+    sessionDate: todaysSolution?.date,
+    sessionToken: todaysSolution?.sessionToken,
+    initialSig: todaysSolution?.initialSig,
+  });
 
   const [isInfoPopUpOpen, setIsInfoPopUpOpen] =
     React.useState<boolean>(firstRun);
diff --git a/src/react-app-env.d.ts b/src/react-app-env.d.ts
index f6733c9..ac88680 100644
--- a/src/react-app-env.d.ts
+++ b/src/react-app-env.d.ts
@@ -1,10 +1,15 @@
 /// <reference types="react-scripts" />
+
 declare global {
   interface ImportMetaEnv {
     readonly VITE_CDN_URL?: string;
+    readonly VITE_HEARDLE_SALT?: string;
+    readonly VITE_HEARDLE_API_URL?: string;
   }
 
   interface ImportMeta {
     readonly env: ImportMetaEnv;
   }
 }
+
+export {};