# Secure channel encryption (/en/realtime-media/broadcast-streaming/build/secure-and-protect-channels/media-stream-encryption/flutter)

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Media stream encryption encrypts audio and video streams with a unique [key](https://en.wikipedia.org/wiki/Public_key_certificate) and [salt](https://en.wikipedia.org/wiki/Salt_%28cryptography%29) controlled by your app server. Encryption ensures that only authorized users in a channel can see and hear each other. RTC SDK provides built-in encryption methods that you can use to guarantee data confidentiality during transmission.

This article describes how to integrate Agora built-in media stream encryption into your app.

## Understand the tech

The following figure illustrates data transfer with media stream encryption enabled.

**Data transfer process**

      
  
      
  
      
  
      
  
      
  
      
  
      
![Encrypted media stream transfer process](https://assets-docs.agora.io/images/video-sdk/encrypt_media_streams_dataTransferProcess.svg)

    
  
      
  
      
  
## Prerequisites

Ensure that you have implemented the [SDK quickstart](../../index) in your project.

## Implement media stream encryption

      
  
      
  
      
  
      
  
      
  
      
  
      
To add built-in media stream encryption to your app, refer to the following steps.

1. Generate a key and salt on your server.

   To generate a random 32-byte hexadecimal key on your server as a string, run:

   ```bash
   openssl rand -hex 32
   ```

   To generate a random Base64-encoded, 32-byte salt on your server, run:

   ```bash
   openssl rand -base64 32
   ```

2. Implement client-side logic.

<CalloutContainer type="info">
  <CalloutDescription>
    All users in a channel must use the same encryption mode, key, and salt. Discrepancies may lead to unexpected behavior, such as black screens or audio loss.

    To ensure security, use a new key and salt each time you enable media stream encryption.
  </CalloutDescription>
</CalloutContainer>

Obtain the string key and Base64-encoded salt from your server, convert the salt from Base64 to `Uint8List`, and call `enableEncryption` before joining a channel. Set the encryption mode to `aes128Gcm2` or `aes256Gcm2` and pass the key and salt to the SDK.

```dart
import 'dart:convert';
import 'dart:typed_data';
import 'package:agora_rtc_engine/agora_rtc_engine.dart';

Future<void> enableEncryption(RtcEngine rtcEngine) async {
  final String encryptionKdfSaltBase64 =
      await Server.getEncryptionKdfSaltBase64();
  final String encryptionSecret = await Server.getEncryptionSecret();
  final Uint8List encryptionKdfSalt = base64Decode(encryptionKdfSaltBase64);

  final config = EncryptionConfig(
    encryptionMode: EncryptionMode.aes128Gcm2,
    encryptionKey: encryptionSecret,
    encryptionKdfSalt: encryptionKdfSalt,
  );

  await rtcEngine.enableEncryption(enabled: true, config: config);
}
```

## Reference

### API reference

* [`enableEncryption`](https://api-ref.agora.io/en/video-sdk/flutter/6.x/API/class_irtcengine.html#api_irtcengine_enableencryption)
* [`EncryptionConfig`](https://api-ref.agora.io/en/video-sdk/flutter/6.x/API/class_encryptionconfig.html)
* [`EncryptionMode`](https://api-ref.agora.io/en/video-sdk/flutter/6.x/API/enum_encryptionmode.html)