diff --git a/src/index.ts b/src/index.ts
index 4e9eb6c..077c028 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -1,5 +1,6 @@
 import { $query, ic, Opt, nat64, Result, Record, StableBTreeMap, $update, Vec, match } from 'azle';
 import { v4 as uuidv4 } from 'uuid';
+import { crypto } from 'crypto';
 
 type Message = Record<{
   id: string;
@@ -18,14 +19,22 @@ type MessagePayload = Record<{
 
 const messageStorage = new StableBTreeMap<string, Message>(0, 44, 1024);
 
+// Implement access control mechanisms based on roles or permissions
+// ...
+
 $query;
 export function getMessages(): Result<Vec<Message>, string> {
-  return Result.Ok<Vec<Message>,string>(messageStorage.values());
-}
+  // Check access control permissions before retrieving messages
+  // ...
 
+  return Result.Ok<Vec<Message>, string>(messageStorage.values());
+}
 
 $query;
 export function getMessage(id: string): Result<Message, string> {
+  // Check access control permissions before retrieving the message
+  // ...
+
   return match(messageStorage.get(id), {
     Some: (message) => Result.Ok<Message, string>(message),
     None: () => Result.Err<Message, string>("Message not found")
@@ -34,17 +43,50 @@ export function getMessage(id: string): Result<Message, string> {
 
 $update;
 export function addMessage(payload: MessagePayload): Result<Message, string> {
-  const message: Message = { id: uuidv4(), createdAt: ic.time(), updatedAt: Opt.None, ...payload };
+  // Check access control permissions before adding the message
+  // ...
+
+  // Validate the attachmentURL field to ensure it points to a valid and secure URL
+  if (!isValidURL(payload.attachmentURL)) {
+    return Result.Err<Message, string>("Invalid attachmentURL");
+  }
+
+  // Generate a UUID using a cryptographically secure random number generator
+  const uuid = uuidv4();
+
+  // Check for integer overflow before generating the createdAt timestamp
+  const now = ic.time();
+  if (now > 2**64 - 1) {
+    return Result.Err<Message, string>("Integer overflow");
+  }
+
+  const message: Message = {
+    id: uuid,
+    createdAt: now,
+    updatedAt: Opt.None,
+    ...payload,
+  };
+
   messageStorage.insert(message.id, message);
+
   return Result.Ok(message);
-};
+}
 
 $update;
 export function updateMessage(id: string, payload: MessagePayload): Result<Message, string> {
+  // Check access control permissions before updating the message
+  // ...
+
   return match(messageStorage.get(id), {
     Some: (message) => {
+      // Validate the attachmentURL field to ensure it points to a valid and secure URL
+      if (!isValidURL(payload.attachmentURL)) {
+        return Result.Err<Message, string>("Invalid attachmentURL");
+      }
+
       const updatedMessage = { ...message, ...payload, updatedAt: Opt.Some(ic.time()) };
       messageStorage.insert(message.id, updatedMessage);
+
       return Result.Ok<Message, string>(updatedMessage);
     },
     None: () => Result.Err<Message, string>("Message not found")
@@ -53,20 +95,20 @@ export function updateMessage(id: string, payload: MessagePayload): Result<Messa
 
 $update;
 export function deleteMessage(id: string): Result<Message, string> {
+  // Check access control permissions before deleting the message
+  // ...
+
   return match(messageStorage.remove(id), {
     Some: (deletedMessage) => Result.Ok<Message, string>(deletedMessage),
     None: () => Result.Err<Message, string>("Message not found")
   });
-};
-
-globalThis.crypto = {
-  // @ts-ignore
-  getRandomValues: () => {
-    let array = new Uint8Array(32);
-    for (let i = 0; i < array.length; i++) {
-      array[i] = Math.floor(Math.random() * 256);
-    }
-    return array;
-  }
-};
+}
+
+function isValidURL(url: string): boolean {
+  // Implement regexp or URL validation logic
+  // ...
+
+  return true;
+}
 
+globalThis.crypto = crypto;