Implement E2EE and message content moderation

apps/mobile/src/lib/encryption/messageDecryption.ts

@@ -0,0 +1,52 @@
+/**
+ * Text Message Decryption
+ * 
+ * Decrypts E2EE text messages using the user's RSA private key.
+ */
+
+import { unwrapAESKey, importAESKey, decryptAES } from './crypto';
+import { base64ToArrayBuffer, base64ToUint8Array } from './utils';
+import type { KeysMetadata, RSAPrivateKeyJWK } from './types';
+
+/**
+ * Decrypt an E2EE text message
+ * 
+ * @param encryptedContent - Base64-encoded ciphertext
+ * @param encryptionIv - Base64-encoded initialization vector
+ * @param keysMetadata - The wrapped keys metadata
+ * @param privateKeyJwk - User's RSA private key
+ * @param isRecipient - Whether the current user is the recipient (true) or sender (false)
+ * @returns The decrypted plaintext message
+ */
+export async function decryptTextMessage(
+  encryptedContent: string,
+  encryptionIv: string,
+  keysMetadata: KeysMetadata,
+  privateKeyJwk: RSAPrivateKeyJWK,
+  isRecipient: boolean
+): Promise<string> {
+  
+  // 1. Select the correct wrapped key
+  const wrappedKeyBase64 = isRecipient
+    ? keysMetadata.recipient_wrapped_key
+    : keysMetadata.sender_wrapped_key;
+
+  if (!wrappedKeyBase64) {
+    throw new Error('No wrapped key available for decryption');
+  }
+
+  // 2. Unwrap AES key using RSA private key
+  const rawAesKey = await unwrapAESKey(wrappedKeyBase64, privateKeyJwk);
+
+  // 3. Import AES key
+  const aesKey = await importAESKey(rawAesKey);
+
+  // 4. Decrypt content
+  const iv = base64ToUint8Array(encryptionIv);
+  const ciphertext = base64ToArrayBuffer(encryptedContent);
+  
+  const plaintext = await decryptAES(ciphertext, aesKey, iv);
+
+  // 5. Decode to string
+  return new TextDecoder().decode(plaintext);
+}