Firefox OS/Remote Control

Introduction

Remote control is a feature for Firefox OS on TV. After Send tab to TV, user can easily extend browsing experience on TV via Firefox on Android, using virtual touchpad to control TV.

Meta Bug: bug 1205939

Prototype Demo Video: http://bit.ly/1Fa2ST1

UX & Visual Spec

UX Spec: http://bit.ly/1jrWqgn

Visual Spec: http://bit.ly/1jrWQU3

Architecture Designs

Remote Control Service: Entry point of remote control feature. Control service related logic and data in runtime.
TLS server: Serves connections from user.

User interaction of remote control is divided into two parts:

Peer authentication
Control event processing

Peer authentication

Remote control is designed to protect data transmitted between client and server, for example: user input string may contains privacy data. The connection is based on self-signed TLS server. To prevent man in the middle(MITM) attack, we adopt J-PAKE to exchange symmetric key for peer authentication. Following describes how it works:

The user opens the URL in the client (e.g. mobile browser).
Client requests the page without a valid UUID.
Server responses the content of the "secure.html" as the requested page for key exchange.
Client requests the RSA public key from "secure.sjs" via AJAX. (Detail)
"Secure.sjs" responses the public key (RSA-OEAP, exported by SPKI) in base64. (source)
Client imports the RSA public key (source), generates a symmetric key (AES-GCM) (source) and wraps it by the public key (RSA-OEAP) (source).
Client sends the wrapped symmetric key to "secure.sjs" in base64 via AJAX. (Detail)
"Secure.sjs" generates a ticket number (a random number for polling only) and responses it to the client immediately.
"Secure.sjs" asynchronously unwraps the symmetric key with the private key (RSA-OEAP). (source)
"Secure.sjs" saves the symmetric key along with a corresponding UUID generated by Remote Control Service.
Remote Control Service encrypts the UUID with its symmetric key, binds it with the ticket number and waits for polling. (The encrypted UUID makes the client be able to confirm if the server stores the symmetric key correctly.) (source)
Client keeps polling the encrypted UUID from "secure.sjs" with the ticket number. (Detail)
Once receiving the encrypted UUID, the client decrypts it and stores it in the cookie.
Client reloads the URL with the valid UUID in the cookie.

PIN code pairing

PIN code is a mechanism to ensure the device connects to TV is physical near TV. While connects to TV, user needs to enter 4 digits PIN code on TV screen. After pass pairing, user is redirected to control page and not need to enter PIN code until: 1) 90 days, pairing expired or 2) user revokes all pairing in remote control app. Pairing can be turned off in remote control app. Following describes how PIN code pairing is done:

User opens the URL.
Client requests page with UUID requires pairing.
Server get the UUID and generate a PIN code.
Remote control service sends PIN code to Gaia system app to trigger pairing notification on screen. (send chrome event)
Server returns pairing.html as requested page for PIN code pairing.
User enter PIN code on screen.
Client encrypts PIN code.
Client sends PIN code to pairing.sjs. Detail
Pairing.sjs replies a ticket number.
Pairing.sjs decrypts PIN code using symmetric key received in establish secure connection. source
Pairing.sjs confirms PIN code correct from remote control service and delete pending PIN code.
Pairing.sjs requests Gaia system app to dismiss pairing notification on screen. (send chrome event)
Client queries PIN code pairing result from pairing.sjs by ticket number. Detail
Client reloads the URL with UUID.

After PIN code pairing, client reloads the URL with a valid UUID and get control page.

Control event processing

Control page provides: 1) a virtual touchpad, 2) a virtual vertical scrollbar, 3) 3 function keys. Every touch, swipe or click will be generated to an event in JSON format, encrypted and send to TV. Following describes how control event is sent and processed:

User opens the URL.
Client requests page with UUID can access control page.
Server returns client.html as requested page for remote control.
User operates control page.
Client generates an event and encrypts the event using symmetric key. source
Client sends encrypted event.
Client.sjs responses with latest event result.
Client.sjs decrypts event with symmetric key received in establish secure connection. source
Client.sjs parses event and dispatch to Gecko or Gaia system app.

Data encryption/decryption

There are three kinds of data are encrypted while tranmission:

Client polls UUID in establish secure connection stage
Client sends PIN code in pin code pairing
Client sends event in control event processing

As data are encrypted by symmetric key, AES-GCM, there are two things need noticed:

AES-GCM need initialization vector(IV) to encrypt/decrypt. Currently, IV is random value for each data, length is 12 bytes. Encrypted data is appended after IV. Receiver needs to slice first 12 bytes as IV to decrypt.
Each message type is string, use TextEncoder.encode() to encode as an UInt8Array, then encrypt to ArrayBuffer. Vice versa.
Data encryption/decryption is asynchronous but HTTP request need response immediately. For UUID and PIN code case, remote control uses a ticket number to get status after decryption. But for event, we reduce polling result but use latest event's result instead.

Ajax Protocol

RSA public key exchange

Request

 {
   action: 'require-public-key'
 }

Response

 {
   publicKey: <RSA-OEAP SPKI in base64>
 }
 {
   error: <reason>
 }

Send symmetric key

Request

 {
   action: 'send-symmetric-key',
   wrappedSymmetricKey: <AES-GCM wrapped by RSA-OEAP in base64>
 }

Response

 {
   ticket: <ticket>
 }
 {
   error: <reason>
 }

Poll UUID

Request

 {
   action: 'poll-uuid'
   ticket: <ticket>
 }

Response

 {
   done: true,
   encryptedUUID: <IV + UUID encrypted by AES-GCM, in base64>,
 }
 {
   done: true,
   error: <reason>
 }
 {
   done: false // Symmetic key unwrapping or encrypting UUID
 }

Pair PIN code

Request

 {
   action: 'pair-pincode'
   encryptedPIN: <IV + PIN encrypted by AES-GCM in base64>
 }

Response

 {
   ticket: <ticket>
 }

Poll pair result

Request

 {
   action: 'poll-pair-result'
   ticket: <ticket>
 }

Response

 {
   done: true
   verified: <boolean>
   reason: <reason>
 }
 {
   done: false
 }

Encrypted control events

Client sends encrypted event in query string as:

 <IP_Address>:<Port>?message=<IV + encrypted event by AES-GCM in base64>

Response

 {
   verified: <boolean>
 }

After decrypted, following are control events:

Touch Events

 {
   type: 'touchstart',
   detail: {
     width: <touch panel width, integer, in pixels>,
     height: <touch panel height, integer, in pixels>,
     identifier: <A simple unique identifier for server to distinguish touch events between different clients, string>
   }
 }

 {
   type: 'touchmove',
   detail: {
     dx: <dx between current point and starting point, integer, in pixels>,
     dy: <dy between current point and starting point, integer, in pixels>,
     identifier: <should be identical with "touchstart">,
     duration: <duration from "touchstart", integer, in milliseconds>
   }
 }

 {
   type: 'touchend',
   detail: {
     dx: <same as "touchmove">,
     dy: <same as "touchmove">,
     identifier: <should be identical with "touchstart">,
     duration: <same as "touchmove">,
     swipe: <the gesture within this touch, string, should be "left", "right", "up" and "down">
   }
 }

Scroll Events

There are "scrollstart", "scrollmove" and "scrollend" events which details are all identical with corresponding touch events above.

Key Events

 {
   type: 'keypress',
   detail: <KeyEvent constant, string, sush as "DOM_VK_RETURN">
 }

Input Events

 {
   type: 'textinput',
   detail: {
     clear: <whether to clear the entire string in the current focused input field, boolean>,
     string: <new string to append, string>,
     keycode: <a specified key to be pressed after the string inputted, integer>
   }
 }

Custom Events

 {
   type: 'custom',
   detail: {
     action: <custom action name, string>,
     ...
   }
 }

Pairing (Full version, without secure connection)

Meta Bug: bug 1207996

Flowchart

First Time Connection (deprecated in secure connection)

Enter PIN Code (deprecated in secure connection)

Resume Connection (deprecated in secure connection)

Dismiss Pairing

Protocol

from client to server via AJAX (deprecated in secure connection)

 {
   pincode: <pincode>
 }

response when success (deprecated in secure connection)

 {
   verified: true,
   uuid: <uuid>
 }

reponse when error

 {
   verified: false,
   reason: 'expired' / 'invalid'
 }

internal events at server side

 {
   type: 'mozChromeRemoteControlEvent',
   detail: {
     action: 'pin-created',
     pincode: <pincode>
   }
 }

 {
   type: 'mozChromeRemoteControlEvent',
   detail: {
     action: 'pin-destroyed'
   }
 }

 {
   type: 'mozContentEvent',
   detail: {
     type: 'remote-control-pin-dismissed',
     detail: {
       reason: 'timeout' / 'manually'
     }
   }
 }

Secure Connection (deprecated)

To protect private data between user and TV, we provide a secure connection which refers to SSL and jCryption. Here is the concept:

Client requests RSA public key from TV.
Client sends symmetric key and PIN code (if any) to TV, encrypted with public key.
TV decrypts symmetric key with private key
TV generates an UUID, encrypts with symmetric key then sends 2 UUIDs to client, one is encrypted the other is not.
Client decrypts UUID with symmetric key, confirm UUID
Begin remote control with symmetric key.

Goal of Remote Control is to create an easy to use way for every device, we hide public key exchange at the background. User doesn't need to input a long URL with public key nor scan QRCode. Everything is done automatically without interrupting user experience.