# Secure channel encryption (/en/realtime-media/video/build/secure-and-protect-channels/media-stream-encryption/ios)

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Media stream encryption refers to encrypting audio and video streams in an app using a unique [key](https://en.wikipedia.org/wiki/Public_key_certificate) and [salt](https://en.wikipedia.org/wiki/Salt_\(cryptography\)) controlled by the app developer. Encryption ensures that only the authorized users in a channel see and hear each other. Video 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 [#understand-the-tech]

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

**Data transfer process**

![EncryptMediaStream](https://assets-docs.agora.io/images/video-sdk/encrypt_media_streams_dataTransferProcess-web.svg)

## Prerequisites [#prerequisites]

Ensure that you have implemented the [SDK quickstart](/en/realtime-media/video/get-started-sdk) in your project.

## Implement media stream encryption [#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, refer to the following `OpenSSL` command:

         ```shell
         # Generate a 32-byte hexadecimal key
         openssl rand -hex 32
         ```

       * To generate a random Base64-encoded, 32-byte salt on your server, refer to the following `OpenSSL` command:

         ```shell
         # Generate a Base64-encoded, 32-byte salt
         openssl rand -base64 32
         ```

    2. Implement client-side logic

       1. To manually add the encryption library to your project:

          1. Copy the `AgoraRtcCryptoLoader.framework` file from the Agora Video SDK package to your project folder.

          2. Open Xcode, go to **TARGETS > Project Name > General > Frameworks, Libraries, and Embedded Content**.

          3. Click **`+`** and choose **Add Other...**, then add `AgoraRtcCryptoLoader.framework`.

          4. To ensure that the dynamic library's signature is consistent with the app's signature, set the **Embed** attribute of the dynamic library to **Embed & Sign**.

          <CalloutContainer type="warning">
            <CalloutTitle>
              note
            </CalloutTitle>

            <CalloutDescription>
              Apple requires that an app's extension not contain dynamic libraries. If you need to integrate the SDK into a dynamic library within an extension, change the file's status to **Do Not Embed**.
            </CalloutDescription>
          </CalloutContainer>

       2. To import the `AgoraRtcCryptoLoader` library, add the following line to the `ViewController.swift` file:

          ```swift
          import AgoraRtcCryptoLoader
          ```

       3. Get the String key and Base64-encoded salt from the server.

       4. Convert the salt from Base64 to `uint8_t`.

       5. Before joining the channel, call `enableEncryption` to set the encryption mode, and pass the key and salt to the SDK.

       <CalloutContainer type="warning">
         <CalloutTitle>
           note
         </CalloutTitle>

         <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, best practice is to use a new key and salt each time you enable media stream encryption.
         </CalloutDescription>
       </CalloutContainer>

       To implement this logic, refer to the following code:

       ```swift
       func getEncryptionSaltFromServer() -> Data {
           let base64Salt = "EncryptionKdfSaltInBase64Strings"
           return Data(base64Encoded: base64Salt)!
       }

       let config = AgoraEncryptionConfig()
       config.encryptionMode = .AES128GCM2
       config.encryptionKdfSalt = getEncryptionSaltFromServer()
       config.encryptionKey = getEncryptionKeyFromServer()
       let ret = agoraKit.enableEncryption(true, encryptionConfig: config)
       if ret != 0 {
           self.showAlert(title: "Error", message: "enableEncryption call failed: \\(ret), please check your params")
       }
       ```

    ### Development considerations [#development-considerations-1]

    The media stream encryption feature is supported in both communication and live broadcasting use-cases. However, in the live broadcasting use-case, Agora does not support pushing the encrypted media stream to CDN.

    ### API reference [#api-reference-1]

    * [`enableEncryption`](https://api-ref.agora.io/en/video-sdk/ios/4.x/documentation/agorartckit/agorartcenginekit/enableencryption\(_\:encryptionconfig:\))
    * [`AgoraEncryptionConfig`](https://api-ref.agora.io/en/video-sdk/ios/4.x/documentation/agorartckit/agoraencryptionconfig/)