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This topic includes details on using end-to-end encryption in the Vonage Video Linux client SDK:

• Setting the encryption secret
• Events and errors

For an overview of end-to-end encryption, see this topic.

Setting the encryption secret

End-to-end encrypted sessions are created using server APIs (see Enabling encryption using the REST API).

Before the client publishes or subscribes, call the otc_session_set_encryption_secret() function:

otc_session_set_encryption_secret(session, secret);	
otc_session_connect(session, TOKEN);

A valid secret is a string between 8 and 256 characters. You can change the secret by calling the otc_session_set_encryption_secret() function again.

Passing an invalid secret will result in an OTC_SESSION_INVALID_ENCRYPTION_SECRET error.

Events and errors

Events and errors are essential to managing the behavior of user-driven encryption behavior. End-to-end encryption uses the shared secret model: everyone in the session is expected to use the same secret to encrypt their media and decrypt everyone else's.

The new error code is OTC_SESSION_INVALID_ENCRYPTION_SECRET and will be returned as the result code of the set_encryption_secret method, not in the on_error callback.

If a client tries to set an invalid encryption secret for a session, the otc_session_callbacks.on_error() returns an error code set to OTC_SESSION_INVALID_ENCRYPTION_SECRET. In the following example, a session is initialized with an empty (and thus invalid) encryption secret:

int result = otc_session_set_encryption_secret(session, "");
if (result == OTC_SESSION_INVALID_ENCRYPTION_SECRET) {
  // Report error...
}

If a user tries to publish in an end-to-end encrypted session without having specified an encryption secret, calling the otc_session_publish() function results in the otc_publisher_callbacks.on_error() fuction being called with an error that has the code set to OTC_SESSION_ENCRYPTION_SECRET_MISSING. For the best user experience, the application should validate a user-supplied secret before calling the otc_session_publish() function:

static void on_publisher_error(otc_publisher *publisher,
                               void *user_data,
                               const char* error_string,
                               enum otc_publisher_error_code error_code) {
  if (otc_publisher_error_code == OTC_SESSION_ENCRYPTION_SECRET_MISSING) {
    // The application should communicate that the secret was not set.
  }
}

struct otc_publisher_callbacks publisher_callbacks = {0};
publisher_callbacks.on_error = on_publisher_error;

session = otc_session_new(API_KEY, SESSION_ID, &session_callbacks);

otc_publisher *publisher = otc_publisher_new("Joe",
                                  nullptr,
                                  &publisher_callbacks);
otc_session_publish(session, publisher);

If a subscriber is unable to decode a stream's media due to an incorrect encryption secret, the subscriber_callbacks.on_error() function is called with an error that has the code set to OTC_SUBSCRIBER_ENCRYPTION_SECRET_MISMATCH. It is important to communicate to the user that media is not being received due to an encryption mismatch and not due to a connection failure or audio/video issue:

static void on_subscriber_error(otc_subscriber *subscriber,
                               void *user_data,
                               const char* error_string,
                               enum otc_subscriber_error_code error_code) {
  if (otc_subscriber_error_code == OTC_SUBSCRIBER_ENCRYPTION_SECRET_MISMATCH) {
  // Activate a UI element communicating that there's been an encryption secret mismatch.
  }
}

struct otc_subscriber_callbacks subscriber_callbacks = {0};
subscriber_callbacks.on_error = on_subscriber_error;

otc_subscriber *subscriber = otc_subscriber_new(stream,
                                                &subscriber_callbacks);
otc_session_subscribe(session, subscriber);

If a subscriber encounters an internal error while decrypting a packet, the subscriber_callbacks.on_error() function is called with an error that has the code set to OTC_SUBSCRIBER_DECRYPTION_INTERNAL_ERROR.