diff --git a/apps/web/src/services/local-ai-chat-repo.ts b/apps/web/src/services/local-ai-chat-repo.ts
index e37c26f..1425a50 100644
--- a/apps/web/src/services/local-ai-chat-repo.ts
+++ b/apps/web/src/services/local-ai-chat-repo.ts
@@ -1,5 +1,10 @@
 import { localDb, type LocalAiChatSessionRecord } from "@/services/local-db";
 import type { WebAiChannel } from "@/services/ai-api";
+import {
+  decryptAiChatSessionRecord,
+  encryptAiChatSessionRecord,
+  shouldEncryptAiChatSessionRecord
+} from "@/services/local-sensitive-codec";
 
 export type LocalAiChatMessageRecord = {
   id: string;
@@ -64,20 +69,33 @@ export async function listLocalAiChatSessions(
   userId: string
 ): Promise<LocalAiChatSessionSnapshot[]> {
   const records = await localDb.aiChatSessions.where("userId").equals(userId).toArray();
-  return records.map(toSnapshot);
+  const encryptedRecords = await Promise.all(
+    records
+      .filter(shouldEncryptAiChatSessionRecord)
+      .map((record) => encryptAiChatSessionRecord(record))
+  );
+
+  if (encryptedRecords.length > 0) {
+    await localDb.aiChatSessions.bulkPut(encryptedRecords);
+  }
+
+  const decryptedRecords = await Promise.all(
+    records.map((record) => decryptAiChatSessionRecord(record))
+  );
+  return decryptedRecords.map(toSnapshot);
 }
 
 export async function saveLocalAiChatSession(
   input: SaveLocalAiChatSessionInput
 ): Promise<LocalAiChatSessionRecord> {
-  const record: LocalAiChatSessionRecord = {
+  const record = await encryptAiChatSessionRecord({
     key: createSessionKey(input.userId, input.channel),
     userId: input.userId,
     channel: input.channel,
     sessionId: input.sessionId,
     messagesJson: JSON.stringify(input.messages),
     updatedAt: Date.now()
-  };
+  });
 
   await localDb.aiChatSessions.put(record);
   return record;
diff --git a/apps/web/src/services/local-crypto.ts b/apps/web/src/services/local-crypto.ts
new file mode 100644
index 0000000..6d8f5ff
--- /dev/null
+++ b/apps/web/src/services/local-crypto.ts
@@ -0,0 +1,126 @@
+const LOCAL_CRYPTO_KEY_STORAGE_KEY = "todolist.web.local-crypto-key";
+const LOCAL_CRYPTO_PREFIX = "locv1";
+const LOCAL_CRYPTO_IV_LENGTH = 12;
+const LOCAL_CRYPTO_KEY_LENGTH = 32;
+
+let cachedLocalCryptoKeyPromise: Promise<CryptoKey> | null = null;
+
+function toArrayBuffer(bytes: Uint8Array): ArrayBuffer {
+  return bytes.buffer.slice(bytes.byteOffset, bytes.byteOffset + bytes.byteLength) as ArrayBuffer;
+}
+
+function bytesToBase64Url(bytes: Uint8Array): string {
+  let binary = "";
+  const chunkSize = 0x8000;
+
+  for (let index = 0; index < bytes.length; index += chunkSize) {
+    const chunk = bytes.subarray(index, index + chunkSize);
+    binary += String.fromCharCode(...chunk);
+  }
+
+  return btoa(binary).replace(/\+/g, "-").replace(/\//g, "_").replace(/=+$/u, "");
+}
+
+function base64UrlToBytes(value: string): Uint8Array {
+  const normalizedValue = value.replace(/-/g, "+").replace(/_/g, "/");
+  const paddedValue = normalizedValue + "=".repeat((4 - (normalizedValue.length % 4 || 4)) % 4);
+  const binary = atob(paddedValue);
+  const bytes = new Uint8Array(binary.length);
+
+  for (let index = 0; index < binary.length; index += 1) {
+    bytes[index] = binary.charCodeAt(index);
+  }
+
+  return bytes;
+}
+
+function createRandomKeyBytes(): Uint8Array {
+  const bytes = new Uint8Array(LOCAL_CRYPTO_KEY_LENGTH);
+  crypto.getRandomValues(bytes);
+  return bytes;
+}
+
+async function resolveLocalCryptoKey(): Promise<CryptoKey> {
+  if (cachedLocalCryptoKeyPromise) {
+    return cachedLocalCryptoKeyPromise;
+  }
+
+  cachedLocalCryptoKeyPromise = (async () => {
+    const savedKey = window.localStorage.getItem(LOCAL_CRYPTO_KEY_STORAGE_KEY);
+    const keyBytes = savedKey ? base64UrlToBytes(savedKey) : createRandomKeyBytes();
+
+    if (!savedKey) {
+      window.localStorage.setItem(LOCAL_CRYPTO_KEY_STORAGE_KEY, bytesToBase64Url(keyBytes));
+    }
+
+    return crypto.subtle.importKey("raw", toArrayBuffer(keyBytes), "AES-GCM", false, [
+      "encrypt",
+      "decrypt"
+    ]);
+  })();
+
+  return cachedLocalCryptoKeyPromise;
+}
+
+export function isLocalEncryptedString(value: string): boolean {
+  return value.startsWith(`${LOCAL_CRYPTO_PREFIX}:`);
+}
+
+export async function encryptLocalString(
+  value: string | null | undefined
+): Promise<string | null | undefined> {
+  if (value === undefined || value === null) {
+    return value;
+  }
+
+  if (isLocalEncryptedString(value)) {
+    return value;
+  }
+
+  const key = await resolveLocalCryptoKey();
+  const iv = crypto.getRandomValues(new Uint8Array(LOCAL_CRYPTO_IV_LENGTH));
+  const plaintext = new TextEncoder().encode(value);
+  const encryptedBuffer = await crypto.subtle.encrypt(
+    {
+      name: "AES-GCM",
+      iv
+    },
+    key,
+    plaintext
+  );
+
+  return `${LOCAL_CRYPTO_PREFIX}:${bytesToBase64Url(iv)}:${bytesToBase64Url(new Uint8Array(encryptedBuffer))}`;
+}
+
+export async function decryptLocalString(
+  value: string | null | undefined
+): Promise<string | null | undefined> {
+  if (value === undefined || value === null) {
+    return value;
+  }
+
+  if (!isLocalEncryptedString(value)) {
+    return value;
+  }
+
+  const [prefix, ivText, encryptedText] = value.split(":");
+  if (prefix !== LOCAL_CRYPTO_PREFIX || !ivText || !encryptedText) {
+    return null;
+  }
+
+  try {
+    const key = await resolveLocalCryptoKey();
+    const decryptedBuffer = await crypto.subtle.decrypt(
+      {
+        name: "AES-GCM",
+        iv: toArrayBuffer(base64UrlToBytes(ivText))
+      },
+      key,
+      toArrayBuffer(base64UrlToBytes(encryptedText))
+    );
+
+    return new TextDecoder().decode(decryptedBuffer);
+  } catch {
+    return null;
+  }
+}
diff --git a/apps/web/src/services/local-sensitive-codec.ts b/apps/web/src/services/local-sensitive-codec.ts
new file mode 100644
index 0000000..54c4c94
--- /dev/null
+++ b/apps/web/src/services/local-sensitive-codec.ts
@@ -0,0 +1,150 @@
+import type {
+  LocalAiChatSessionRecord,
+  LocalOpLogRecord,
+  LocalSyncInboxRecord,
+  LocalTaskDraftRecord,
+  LocalTaskRecord
+} from "@/services/local-db";
+import {
+  decryptLocalString,
+  encryptLocalString,
+  isLocalEncryptedString
+} from "@/services/local-crypto";
+
+export function shouldEncryptTaskRecord(record: LocalTaskRecord): boolean {
+  return (
+    !isLocalEncryptedString(record.title) ||
+    (typeof record.contentJson === "string" && !isLocalEncryptedString(record.contentJson)) ||
+    (typeof record.contentText === "string" && !isLocalEncryptedString(record.contentText))
+  );
+}
+
+export async function encryptTaskRecord(record: LocalTaskRecord): Promise<LocalTaskRecord> {
+  return {
+    ...record,
+    title: (await encryptLocalString(record.title)) ?? record.title,
+    contentJson: (await encryptLocalString(record.contentJson)) ?? null,
+    contentText: (await encryptLocalString(record.contentText)) ?? null
+  };
+}
+
+export async function decryptTaskRecord(record: LocalTaskRecord): Promise<LocalTaskRecord> {
+  const title = await decryptLocalString(record.title);
+  const contentJson = await decryptLocalString(record.contentJson);
+  const contentText = await decryptLocalString(record.contentText);
+
+  return {
+    ...record,
+    title: typeof title === "string" && title.trim().length > 0 ? title : "未命名任务",
+    contentJson: typeof contentJson === "string" ? contentJson : null,
+    contentText: typeof contentText === "string" ? contentText : null
+  };
+}
+
+export function shouldEncryptTaskDraft(record: LocalTaskDraftRecord): boolean {
+  return (
+    !isLocalEncryptedString(record.title) ||
+    (typeof record.contentJson === "string" && !isLocalEncryptedString(record.contentJson)) ||
+    !isLocalEncryptedString(record.contentText)
+  );
+}
+
+export async function encryptTaskDraftRecord(
+  record: LocalTaskDraftRecord
+): Promise<LocalTaskDraftRecord> {
+  return {
+    ...record,
+    title: (await encryptLocalString(record.title)) ?? record.title,
+    contentJson: (await encryptLocalString(record.contentJson)) ?? null,
+    contentText: (await encryptLocalString(record.contentText)) ?? ""
+  };
+}
+
+export async function decryptTaskDraftRecord(
+  record: LocalTaskDraftRecord
+): Promise<LocalTaskDraftRecord> {
+  const title = await decryptLocalString(record.title);
+  const contentJson = await decryptLocalString(record.contentJson);
+  const contentText = await decryptLocalString(record.contentText);
+
+  return {
+    ...record,
+    title: typeof title === "string" ? title : "",
+    contentJson: typeof contentJson === "string" ? contentJson : null,
+    contentText: typeof contentText === "string" ? contentText : ""
+  };
+}
+
+export function shouldEncryptOpLogRecord(record: LocalOpLogRecord): boolean {
+  return !isLocalEncryptedString(record.payload);
+}
+
+export async function encryptOpLogRecord(record: LocalOpLogRecord): Promise<LocalOpLogRecord> {
+  return {
+    ...record,
+    payload: (await encryptLocalString(record.payload)) ?? record.payload
+  };
+}
+
+export async function decryptOpLogRecord(record: LocalOpLogRecord): Promise<LocalOpLogRecord> {
+  const payload = await decryptLocalString(record.payload);
+
+  return {
+    ...record,
+    payload: typeof payload === "string" ? payload : record.payload
+  };
+}
+
+export function shouldEncryptSyncInboxRecord(record: LocalSyncInboxRecord): boolean {
+  return typeof record.payload === "string" && !isLocalEncryptedString(record.payload);
+}
+
+export async function encryptSyncInboxRecord(
+  record: LocalSyncInboxRecord
+): Promise<LocalSyncInboxRecord> {
+  return {
+    ...record,
+    payload: (await encryptLocalString(record.payload)) ?? null
+  };
+}
+
+export async function decryptSyncInboxRecord(
+  record: LocalSyncInboxRecord
+): Promise<LocalSyncInboxRecord> {
+  const payload = await decryptLocalString(record.payload);
+
+  return {
+    ...record,
+    payload: typeof payload === "string" ? payload : null
+  };
+}
+
+export function shouldEncryptAiChatSessionRecord(record: LocalAiChatSessionRecord): boolean {
+  return (
+    !isLocalEncryptedString(record.messagesJson) ||
+    (typeof record.sessionId === "string" && !isLocalEncryptedString(record.sessionId))
+  );
+}
+
+export async function encryptAiChatSessionRecord(
+  record: LocalAiChatSessionRecord
+): Promise<LocalAiChatSessionRecord> {
+  return {
+    ...record,
+    sessionId: (await encryptLocalString(record.sessionId)) ?? null,
+    messagesJson: (await encryptLocalString(record.messagesJson)) ?? "[]"
+  };
+}
+
+export async function decryptAiChatSessionRecord(
+  record: LocalAiChatSessionRecord
+): Promise<LocalAiChatSessionRecord> {
+  const sessionId = await decryptLocalString(record.sessionId);
+  const messagesJson = await decryptLocalString(record.messagesJson);
+
+  return {
+    ...record,
+    sessionId: typeof sessionId === "string" ? sessionId : null,
+    messagesJson: typeof messagesJson === "string" ? messagesJson : "[]"
+  };
+}
diff --git a/apps/web/src/services/local-sync-repo.ts b/apps/web/src/services/local-sync-repo.ts
index 87d13e9..267eca3 100644
--- a/apps/web/src/services/local-sync-repo.ts
+++ b/apps/web/src/services/local-sync-repo.ts
@@ -1,19 +1,36 @@
-import {
+import {
   localDb,
   type LocalOpLogRecord,
   type LocalSyncInboxRecord,
   type LocalSyncStateRecord
 } from "@/services/local-db";
+import {
+  decryptOpLogRecord,
+  decryptSyncInboxRecord,
+  encryptOpLogRecord,
+  encryptSyncInboxRecord,
+  shouldEncryptOpLogRecord,
+  shouldEncryptSyncInboxRecord
+} from "@/services/local-sensitive-codec";
 import type { SyncPullItem } from "@/services/sync-api";
 
 export const MAX_SYNC_RETRY_COUNT = 5;
 
 export async function listPendingSyncOperations(limit = 20): Promise<LocalOpLogRecord[]> {
   const records = await localDb.opLogs.orderBy("clientTs").toArray();
+  const encryptedRecords = await Promise.all(
+    records.filter(shouldEncryptOpLogRecord).map((record) => encryptOpLogRecord(record))
+  );
 
-  return records
+  if (encryptedRecords.length > 0) {
+    await localDb.opLogs.bulkPut(encryptedRecords);
+  }
+
+  const pendingRecords = records
     .filter((record) => record.syncedAt === null && record.retryCount < MAX_SYNC_RETRY_COUNT)
     .slice(0, limit);
+
+  return Promise.all(pendingRecords.map((record) => decryptOpLogRecord(record)));
 }
 
 export async function countPendingSyncOperations(): Promise<number> {
@@ -100,19 +117,23 @@ export async function enqueueRemoteSyncOperations(
   }
 
   const receivedAt = Date.now();
-  const records: LocalSyncInboxRecord[] = operations.map((operation) => ({
-    opId: operation.opId,
-    userId,
-    entityId: operation.entityId,
-    entityType: operation.entityType,
-    action: operation.action,
-    payload: operation.payload,
-    clientTs: operation.clientTs,
-    deviceId: operation.deviceId,
-    serverTs: new Date(operation.serverTs).getTime(),
-    receivedAt,
-    appliedAt: null
-  }));
+  const records = await Promise.all(
+    operations.map(async (operation) =>
+      encryptSyncInboxRecord({
+        opId: operation.opId,
+        userId,
+        entityId: operation.entityId,
+        entityType: operation.entityType,
+        action: operation.action,
+        payload: operation.payload,
+        clientTs: operation.clientTs,
+        deviceId: operation.deviceId,
+        serverTs: new Date(operation.serverTs).getTime(),
+        receivedAt,
+        appliedAt: null
+      })
+    )
+  );
 
   await localDb.syncInbox.bulkPut(records);
   return records.length;
@@ -123,8 +144,15 @@ export async function listPendingRemoteOperations(
   limit = 100
 ): Promise<LocalSyncInboxRecord[]> {
   const records = await localDb.syncInbox.where("userId").equals(userId).toArray();
+  const encryptedRecords = await Promise.all(
+    records.filter(shouldEncryptSyncInboxRecord).map((record) => encryptSyncInboxRecord(record))
+  );
 
-  return records
+  if (encryptedRecords.length > 0) {
+    await localDb.syncInbox.bulkPut(encryptedRecords);
+  }
+
+  const pendingRecords = records
     .filter((record) => record.appliedAt === null)
     .sort((left, right) => {
       if (left.serverTs !== right.serverTs) {
@@ -138,6 +166,8 @@ export async function listPendingRemoteOperations(
       return left.opId.localeCompare(right.opId);
     })
     .slice(0, limit);
+
+  return Promise.all(pendingRecords.map((record) => decryptSyncInboxRecord(record)));
 }
 
 export async function markRemoteOperationsApplied(
diff --git a/apps/web/src/services/local-task-draft-repo.ts b/apps/web/src/services/local-task-draft-repo.ts
index 67220da..e34446e 100644
--- a/apps/web/src/services/local-task-draft-repo.ts
+++ b/apps/web/src/services/local-task-draft-repo.ts
@@ -1,4 +1,9 @@
 import { localDb, type LocalTaskDraftRecord } from "@/services/local-db";
+import {
+  decryptTaskDraftRecord,
+  encryptTaskDraftRecord,
+  shouldEncryptTaskDraft
+} from "@/services/local-sensitive-codec";
 
 export type SaveLocalTaskDraftInput = {
   taskId: string;
@@ -12,7 +17,16 @@ export type SaveLocalTaskDraftInput = {
 };
 
 export async function getLocalTaskDraft(taskId: string): Promise<LocalTaskDraftRecord | undefined> {
-  return localDb.taskDrafts.get(taskId);
+  const draft = await localDb.taskDrafts.get(taskId);
+  if (!draft) {
+    return undefined;
+  }
+
+  if (shouldEncryptTaskDraft(draft)) {
+    await localDb.taskDrafts.put(await encryptTaskDraftRecord(draft));
+  }
+
+  return decryptTaskDraftRecord(draft);
 }
 
 export async function saveLocalTaskDraft(
@@ -23,7 +37,7 @@ export async function saveLocalTaskDraft(
     updatedAt: Date.now()
   };
 
-  await localDb.taskDrafts.put(draft);
+  await localDb.taskDrafts.put(await encryptTaskDraftRecord(draft));
   return draft;
 }
 
diff --git a/apps/web/src/services/local-task-repo.ts b/apps/web/src/services/local-task-repo.ts
index b611047..a9af409 100644
--- a/apps/web/src/services/local-task-repo.ts
+++ b/apps/web/src/services/local-task-repo.ts
@@ -6,6 +6,12 @@
   type LocalTaskStatus,
   type SyncActionType
 } from "@/services/local-db";
+import {
+  decryptTaskRecord,
+  encryptOpLogRecord,
+  encryptTaskRecord,
+  shouldEncryptTaskRecord
+} from "@/services/local-sensitive-codec";
 
 const DEVICE_ID_STORAGE_KEY = "todolist.web.device-id";
 
@@ -83,7 +89,16 @@ function createSyncTaskPayload(payload: SyncTaskPayload): string {
 
 export async function listLocalTasksByUser(userId: string): Promise<LocalTaskRecord[]> {
   const tasks = await localDb.tasks.where("userId").equals(userId).toArray();
-  return tasks
+  const encryptedTasks = await Promise.all(
+    tasks.filter(shouldEncryptTaskRecord).map((task) => encryptTaskRecord(task))
+  );
+
+  if (encryptedTasks.length > 0) {
+    await localDb.tasks.bulkPut(encryptedTasks);
+  }
+
+  const decryptedTasks = await Promise.all(tasks.map((task) => decryptTaskRecord(task)));
+  return decryptedTasks
     .filter((task) => task.deletedAt === null)
     .sort((left, right) => right.updatedAt - left.updatedAt);
 }
@@ -94,7 +109,11 @@ export async function getLocalTaskById(id: string): Promise<LocalTaskRecord | un
     return undefined;
   }
 
-  return task;
+  if (shouldEncryptTaskRecord(task)) {
+    await localDb.tasks.put(await encryptTaskRecord(task));
+  }
+
+  return decryptTaskRecord(task);
 }
 
 export async function createLocalTask(input: CreateLocalTaskInput): Promise<LocalTaskRecord> {
@@ -134,8 +153,8 @@ export async function createLocalTask(input: CreateLocalTaskInput): Promise<Loca
   );
 
   await localDb.transaction("rw", localDb.tasks, localDb.opLogs, async () => {
-    await localDb.tasks.add(task);
-    await localDb.opLogs.add(opLog);
+    await localDb.tasks.add(await encryptTaskRecord(task));
+    await localDb.opLogs.add(await encryptOpLogRecord(opLog));
   });
 
   return task;
@@ -178,8 +197,8 @@ export async function updateLocalTask(
   );
 
   await localDb.transaction("rw", localDb.tasks, localDb.opLogs, async () => {
-    await localDb.tasks.put(nextTask);
-    await localDb.opLogs.add(opLog);
+    await localDb.tasks.put(await encryptTaskRecord(nextTask));
+    await localDb.opLogs.add(await encryptOpLogRecord(opLog));
   });
 
   return nextTask;
@@ -211,8 +230,8 @@ export async function deleteLocalTask(id: string): Promise<boolean> {
   );
 
   await localDb.transaction("rw", localDb.tasks, localDb.opLogs, async () => {
-    await localDb.tasks.put(nextTask);
-    await localDb.opLogs.add(opLog);
+    await localDb.tasks.put(await encryptTaskRecord(nextTask));
+    await localDb.opLogs.add(await encryptOpLogRecord(opLog));
   });
 
   return true;
diff --git a/apps/web/src/services/storage-quota.ts b/apps/web/src/services/storage-quota.ts
index 27445ed..50f76eb 100644
--- a/apps/web/src/services/storage-quota.ts
+++ b/apps/web/src/services/storage-quota.ts
@@ -1,4 +1,4 @@
-import { localDb } from "@/services/local-db";
+import { listLocalTasksByUser } from "@/services/local-task-repo";
 
 export const DEFAULT_CLOUD_QUOTA_BYTES = 100 * 1024 * 1024;
 
@@ -18,13 +18,9 @@ function measureTextBytes(value: string | null): number {
 }
 
 export async function getStorageQuotaSnapshot(userId: string): Promise<StorageQuotaSnapshot> {
-  const tasks = await localDb.tasks.where("userId").equals(userId).toArray();
+  const tasks = await listLocalTasksByUser(userId);
 
   const usedBytes = tasks.reduce((total, task) => {
-    if (task.deletedAt !== null) {
-      return total;
-    }
-
     return (
       total +
       measureTextBytes(task.title) +
diff --git a/apps/web/src/services/sync-merge.ts b/apps/web/src/services/sync-merge.ts
index 666d919..22a299d 100644
--- a/apps/web/src/services/sync-merge.ts
+++ b/apps/web/src/services/sync-merge.ts
@@ -1,4 +1,4 @@
-import {
+import {
   localDb,
   type LocalSyncInboxRecord,
   type LocalTaskPriority,
@@ -6,6 +6,11 @@ import {
   type LocalTaskStatus
 } from "@/services/local-db";
 import { listPendingRemoteOperations } from "@/services/local-sync-repo";
+import {
+  decryptTaskRecord,
+  encryptTaskRecord,
+  shouldEncryptTaskRecord
+} from "@/services/local-sensitive-codec";
 
 const TASK_PRIORITY_VALUES: LocalTaskPriority[] = ["LOW", "MEDIUM", "HIGH", "URGENT"];
 const TASK_STATUS_VALUES: LocalTaskStatus[] = ["TODO", "IN_PROGRESS", "DONE", "ARCHIVED"];
@@ -246,11 +251,14 @@ export async function applyPendingRemoteOperations(userId: string): Promise<numb
         continue;
       }
 
-      const currentTask = await localDb.tasks.get(operation.entityId);
+      const storedTask = await localDb.tasks.get(operation.entityId);
+      const currentTask = storedTask ? await decryptTaskRecord(storedTask) : undefined;
       const incomingTask = buildIncomingTaskRecord(operation, currentTask);
 
       if (shouldApplyIncomingTask(currentTask, incomingTask, operation)) {
-        await localDb.tasks.put(incomingTask);
+        await localDb.tasks.put(await encryptTaskRecord(incomingTask));
+      } else if (storedTask && currentTask && shouldEncryptTaskRecord(storedTask)) {
+        await localDb.tasks.put(await encryptTaskRecord(currentTask));
       }
 
       await localDb.syncInbox.update(operation.opId, { appliedAt });