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WhatsApp Web reverse engineered

Introduction

This project intends to provide a complete description and re-implementation of the WhatsApp Web API, which will eventually lead to a custom client. WhatsApp Web internally works using WebSockets; this project does as well.

Trying it out

Before you can run the application, make sure that you have the following software installed:

  • Node.js (at least version 8, as the async await syntax is used)
  • the CSS preprocessor Ruby Sass (which in turn you need Ruby for)
    • gem install sass for Windows and sudo gem install sass for Linux and OSX.
  • Python 2.7 with the following pip packages installed:
    • websocket-client and git+https://github.com/dpallot/simple-websocket-server.git for acting as WebSocket server and client.
    • curve25519-donna and pycrypto for the encryption stuff.
    • pyqrcode for QR code generation.
    • protobuf for reading and writing the binary conversation format.
  • Note: On Windows curve25519-donna requires Microsoft Visual C++ 9.0 and you need to copy stdint.h into C:\Users\YOUR USERNAME\AppData\Local\Programs\Common\Microsoft\Visual C++ for Python\9.0\VC\include.

Before starting the application for the first time, run npm install to install all Node and pip install -r requirements.txt for all Python dependencies.

Lastly, to finally launch it, just run npm start on Linux based OS's and npm run win on Windows. Using fancy concurrently and nodemon magic, all three local components will be started after each other and when you edit a file, the changed module will automatically restart to apply the changes.

Decryption routine reimplementations

JavaScript

A recent addition is a version of the decryption routine translated to in-browser JavaScript. Run node index_jsdemo.js (just needed because browsers don't allow changing HTTP headers for WebSockets), then open client/login-via-js-demo.html as a normal file in any browser. The console output should show decrypted binary messages after scanning the QR code.

Application architecture

The project is organized in the following way. Note the used ports and make sure that they are not in use elsewhere before starting the application. whatsapp-web-reveng Application architecture

Login and encryption details

WhatsApp Web encrypts the data using several different algorithms. These include AES 256 CBC, Curve25519 as Diffie-Hellman key agreement scheme, HKDF for generating the extended shared secret and HMAC with SHA256.

Starting the WhatsApp Web session happens by just connecting to one of its websocket servers at wss://w[1-8].web.whatsapp.com/ws (wss:// means that the websocket connection is secure; w[1-8] means that any number between 1 and 8 can follow the w). Also make sure that, when establishing the connection, the HTTP header Origin: https://web.whatsapp.com is set, otherwise the connection will be rejected.

Messages

When you send messages to a WhatsApp Web websocket, they need to be in a specific format. It is quite simple and looks like messageTag,JSON, e.g. 1515590796,["data",123]. Note that apparently the message tag can be anything. This application mostly uses the current timestamp as tag, just to be a bit unique. WhatsApp itself often uses message tags like s1, 1234.--0 or something like that. Obviously the message tag may not contain a comma. Additionally, JSON objects are possible as well as payload.

Logging in

To log in at an open websocket, follow these steps:

  1. Generate your own clientId, which needs to be 16 base64-encoded bytes (i.e. 25 characters). This application just uses 16 random bytes, i.e. base64.b64encode(os.urandom(16)) in Python.
  2. Decide for a tag for your message, which is more or less arbitrary (see above). This application uses the current timestamp (in seconds) for that. Remember this tag for later.
  3. The message you send to the websocket looks like this: messageTag,["admin","init",[0,2,7314],["Long browser description","ShortBrowserDesc"],"clientId",true].
    • Obviously, you need to replace messageTag and clientId by the values you chose before
    • The [0,2,7314] part specifies the current WhatsApp Web version. The last value changes frequently. It should be quite backwards-compatible though.
    • "Long browser description" is an arbitrary string that will be shown in the WhatsApp app in the list of registered WhatsApp Web clients after you scan the QR code.
    • "ShortBrowserDesc" has not been observed anywhere yet but is arbitrary as well.
  4. After a few moments, your websocket will receive a message in the specified format with the message tag you chose in step 2. The JSON object of this message has the following attributes:
    • status: should be 200
    • ref: in the application, this is treated as the server ID; important for the QR generation, see below
    • ttl: is 20000, maybe the time after the QR code becomes invalid
    • update: a boolean flag
    • curr: the current WhatsApp Web version, e.g. 0.2.7314
    • time: the timestamp the server responded at, as floating-point milliseconds, e.g. 1515592039037.0

QR code generation

  1. Generate your own private key with Curve25519, e.g. curve25519.Private().
  2. Get the public key from your private key, e.g. privateKey.get_public().
  3. Obtain the string later encoded by the QR code by concatenating the following values with a comma:
    • the server ID, i.e. the ref attribute from step 4
    • the base64-encoded version of your public key, i.e. base64.b64encode(publicKey.serialize())
    • your client ID
  4. Turn this string into an image (e.g. using pyqrcode) and scan it using the WhatsApp app.

Requesting new ref for QR code generation (not implemented)

  1. You can request up to 5 new server refs when previous one expires (ttl).
  2. Do it by sending messageTag,["admin","Conn","reref"].
  3. The server responds with JSON with the following attributes:
    • status: should be 200 (other ones: 304 - reuse previous ref, 429 - new ref denied)
    • ref: new ref
    • ttl: expiration time
  4. Update your QR code with the new ref.

After scanning the QR code

  1. Immediately after you scan the QR code, the websocket receives several important JSON messages that build up the encryption details. These use the specified message format and have a JSON array as payload. Their message tag has no special meaning. The first entry of the JSON array has one of the following values:
    • Conn: array contains JSON object as second element with connection information containing the following attributes and many more:
      • battery: the current battery percentage of your phone
      • browserToken: used to logout without active WebSocket connection (not implemented yet)
      • clientToken: used to resuming closed sessions aka "Remember me" (not implemented yet)
      • phone: an object with detailed information about your phone, e.g. device_manufacturer, device_model, os_build_number, os_version
      • platform: your phone OS, e.g. android
      • pushname: the name of yours you provided WhatsApp
      • secret (remember this!)
      • serverToken: used to resuming closed sessions aka "Remember me" (not implemented yet)
      • wid: your phone number in the chat identification format (see below)
    • Stream: array has four elements in total, so the entire payload is like ["Stream","update",false,"0.2.7314"]
    • Props: array contains JSON object as second element with several properties like imageMaxKBytes (1024), maxParticipants (257), videoMaxEdge (960) and others

Key generation

  1. You are now ready for generating the final encryption keys. Start by decoding the secret from Conn as base64 and storing it as secret. This decoded secret will be 144 bytes long.
  2. Take the first 32 bytes of the decoded secret and use it as a public key. Together with your private key, generate a shared key out of it and call it sharedSecret. The application does it using privateKey.get_shared_key(curve25519.Public(secret[:32]), lambda a:a).
  3. Extend sharedSecret to 80 bytes using HKDF. Call this value sharedSecretExpanded.
  4. This step is optional, it validates the data provided by the server. The method is called HMAC validation. Do it by first calculating HmacSha256(sharedSecretExpanded[32:64], secret[:32] + secret[64:]). Compare this value to secret[32:64]. If they are not equal, abort the login.
  5. You now have the encrypted keys: store sharedSecretExpanded[64:] + secret[64:] as keysEncrypted.
  6. The encrypted keys now need to be decrypted using AES with sharedSecretExpanded[:32] as key, i.e. store AESDecrypt(sharedSecretExpanded[:32], keysEncrypted) as keysDecrypted.
  7. The keysDecrypted variable is 64 bytes long and contains two keys, each 32 bytes long. The encKey is used for decrypting binary messages sent to you by the WhatsApp Web server or encrypting binary messages you send to the server. The macKey is needed to validate the messages sent to you:
    • encKey: keysDecrypted[:32]
    • macKey: keysDecrypted[32:64]

Restoring closed sessions (not implemented)

  1. After sending init command, check whether you have serverToken and clientToken.
  2. If so, send messageTag,["admin","login","clientToken","serverToken","clientId","takeover"]
  3. The server should respond with {"status": 200}. Other statuses:
    • 401: Unpaired from the phone
    • 403: Access denied, check tos field in the JSON: if it equals or greater than 2, you have violated TOS
    • 405: Already logged in
    • 409: Logged in from another location

Resolving challenge (not implemented)

  1. When using old or expired serverToken and clientToken, you will be challenged to confirm that you still have valid encryption keys.
  2. The challenge looks like this messageTag,["Cmd",{"type":"challenge","challenge":"BASE_64_ENCODED_STRING=="}]
  3. Decode challenge string from Base64, sign it with your macKey, encode it back with Base64 and send messageTag,["admin","challenge","BASE_64_ENCODED_STRING==","serverToken","clientId"]
  4. The server should respond with {"status": 200}, but it means nothing.
  5. After solving challenge your connection should be restored.

Logging out

  1. When you have an active WebSocket connection, just send goodbye,,["admin","Conn","disconnect"].
  2. When you don't have such connection (for example your session has been taken over from another location), sign your encKey with your macKey and encode it with Base64. Let's say it is your logoutToken.
  3. Send a POST request to https://dyn.web.whatsapp.com/logout?t=browserToken&m=logoutToken
  4. Remember to always clear your sessions, so sessions list in your phone will not grow big.

Validating and decrypting messages

Now that you have the two keys, validating and decrypting messages the server sent to you is quite easy. Note that this is only needed for binary messages, all JSON you receive stays plain. The binary messages always have 32 bytes at the beginning that specify the HMAC checksum. Both JSON and binary messages have a message tag at their very start that can be discarded, i.e. only the portion after the first comma character is significant.

  1. Validate the message by hashing the actual message content with the macKey (here messageContent is the entire binary message): HmacSha256(macKey, messageContent[32:]). If this value is not equal to messageContent[:32], the message sent to you by the server is invalid and should be discarded.
  2. Decrypt the message content using AES and the encKey: AESDecrypt(encKey, messageContent[32:]).

The data you get in the final step has a binary format which is described in the following. Even though it's binary, you can still see several strings in it, especially the content of messages you sent is quite obvious there.

Binary message format

Binary decoding

The Python script backend/decoder.py implements the MessageParser class. It is able to create a JSON structure out of binary data in which the data is still organized in a rather messy way. The section about Node Handling below will discuss how the nodes are reorganized afterwards.

MessageParser initially just needs some data and then processes it byte by byte, i.e. as a stream. It has a couple of constants and a lot of methods which all build on each other.

Constants

  • Tags with their respective integer values
    • LIST_EMPTY: 0
    • STREAM_8: 2
    • DICTIONARY_0: 236
    • DICTIONARY_1: 237
    • DICTIONARY_2: 238
    • DICTIONARY_3: 239
    • LIST_8: 248
    • LIST_16: 249
    • JID_PAIR: 250
    • HEX_8: 251
    • BINARY_8: 252
    • BINARY_20: 253
    • BINARY_32: 254
    • NIBBLE_8: 255
  • Tokens are a long list of 151 strings in which the indices matter:
    • [None,None,None,"200","400","404","500","501","502","action","add", "after","archive","author","available","battery","before","body", "broadcast","chat","clear","code","composing","contacts","count", "create","debug","delete","demote","duplicate","encoding","error", "false","filehash","from","g.us","group","groups_v2","height","id", "image","in","index","invis","item","jid","kind","last","leave", "live","log","media","message","mimetype","missing","modify","name", "notification","notify","out","owner","participant","paused", "picture","played","presence","preview","promote","query","raw", "read","receipt","received","recipient","recording","relay", "remove","response","resume","retry","s.whatsapp.net","seconds", "set","size","status","subject","subscribe","t","text","to","true", "type","unarchive","unavailable","url","user","value","web","width", "mute","read_only","admin","creator","short","update","powersave", "checksum","epoch","block","previous","409","replaced","reason", "spam","modify_tag","message_info","delivery","emoji","title", "description","canonical-url","matched-text","star","unstar", "media_key","filename","identity","unread","page","page_count", "search","media_message","security","call_log","profile","ciphertext", "invite","gif","vcard","frequent","privacy","blacklist","whitelist", "verify","location","document","elapsed","revoke_invite","expiration", "unsubscribe","disable"]

Number reformatting

  • Unpacking nibbles: Returns the ASCII representation for numbers between 0 and 9. Returns - for 10, . for 11 and \0 for 15.
  • Unpacking hex values: Returns the ASCII representation for numbers between 0 and 9 or letters between A and F (i.e. uppercase) for numbers between 10 and 15.
  • Unpacking bytes: Expects a tag as an additional parameter, namely NIBBLE_8 or HEX_8. Unpacks a nibble or hex value accordingly.

Number formats

  • Byte: A plain ol' byte.
  • Integer with N bytes: Reads N bytes and builds a number out of them. Can be little or big endian; if not specified otherwise, big endian is used. Note that no negative values are possible.
  • Int16: An integer with two bytes, read using Integer with N bytes.
  • Int20: Consumes three bytes and constructs an integer using the last four bits of the first byte and the entire second and third byte. Is therefore always big endian.
  • Int32: An integer with four bytes, read using Integer with N bytes.
  • Int64: An integer with eight bytes, read using Integer with N bytes.
  • Packed8: Expects a tag as an additional parameter, namely NIBBLE_8 or HEX_8. Returns a string.
    • First reads a byte n and does the following n&127 many times: Reads a byte l and for each nibble, adds the result of its unpacked version to the return value (using unpacking bytes with the given tag). Most significant nibble first.
    • If the most significant bit of n was set, removes the last character of the return value.

Helper methods

  • Read bytes: Reads and returns the specified number of bytes.
  • Check for list tag: Expects a tag as parameter and returns true if the tag is LIST_EMPTY, LIST_8 or LIST_16 (i.e. 0, 248 or 249).
  • Read list size: Expects a list tag as parameter. Returns 0 for LIST_EMPTY, returns a read byte for LIST_8 or a read Int16 for LIST_16.
  • Read a string from characters: Expects the string length as parameter, reads this many bytes and returns them as a string.
  • Get a token: Expects an index to the array of Tokens, and returns the respective string.
  • Get a double token: Expects two integers a and b and gets the token at index a*256+b.

Strings

Reading a string needs a tag as parameter. Depending on this tag, different data is read.

  • If the tag is between 3 and 235, the token (i.e. a string) of this tag is got. If the token is "s.whatsapp.net", "c.us" is returned instead, otherwise the token is returned as is.
  • If the tag is between DICTIONARY_0 and DICTIONARY_3, a double token is returned, with tag-DICTIONARY_0 as first and a read byte as second parameter.
  • LIST_EMPTY: Nothing is returned (e.g. None).
  • BINARY_8: A byte is read which is then used to read a string from characters with this length.
  • BINARY_20: An Int20 is read which is then used to read a string from characters with this length.
  • BINARY_32: An Int32 is read which is then used to read a string from characters with this length.
  • JID_PAIR
    • First, a byte is read which is then used to read a string i with this tag.
    • Second, another byte is read which is then used to read a string j with this tag.
    • Finally, i and j are joined together with an @ sign and the result is returned.
  • NIBBLE_8 or HEX_8: A Packed8 with this tag is returned.

Attribute lists

Reading an attribute list needs the number of attributes to read as parameter. An attribute list is always a JSON object. For each attribute read, the following steps are executed for getting key-value pairs (exactly in this order!):

  • Key: A byte is read which is then used to read a string with this tag.
  • Value: A byte is read which is then used to read a string with this tag.

Nodes

A node always consists of a JSON array with exactly three entries: description, attributes and content. The following steps are needed to read a node:

  1. A list size a is read by using a read byte as the tag. The list size 0 is invalid.
  2. The description tag is read as a byte. The value 2 is invalid for this tag. The description string descr is then obtained by reading a string with this tag.
  3. The attributes object attrs is read by reading an attributes object with length (a-2 + a%2) >> 1.
  4. If a was odd, this node does not have any content, i.e. [descr, attrs, None] is returned.
  5. For getting the node's content, first a byte, i.e. a tag is read. Depending on this tag, different types of content emerge:
    • If the tag is a list tag, a list is read using this tag (see below for lists).
    • BINARY_8: A byte is read which is then used as length for reading bytes.
    • BINARY_20: An Int20 is read which is then used as length for reading bytes.
    • BINARY_32: An Int32 is read which is then used as length for reading bytes.
    • If the tag is something else, a string is read using this tag.
  6. Eventually, [descr, attrs, content] is returned.

Lists

Reading a list requires a list tag (i.e. LIST_EMPTY, LIST_8 or LIST_16). The length of the list is then obtained by reading a list size using this tag. For each list entry, a node is read.

Node Handling

After a binary message has been transformed into JSON, it is still rather hard to read. That's why, internally, WhatsApp Web completely retransforms this structure into something that can be easily processed and eventually translated into user interface content. This section will deal with this and awaits completion.

Binary conversation format

When a node has been read, the contents of messages that have been actually sent by the user (i.e. text, image, audio, video etc.) are still not directly visible or accessible via the JSON. Instead, they are kept in a protobuf message. See here for the definitions. The "wrapper" message type is WebMessageInfo.

WhatsApp Web API

WhatsApp Web itself has an interesting API as well. You can even try it out directly in your browser. Just log in at the normal https://web.whatsapp.com/, then open the browser development console. Now enter something like the following (see below for details on the chat identification):

  • window.Store.Wap.profilePicFind("49123456789@c.us").then(res => console.log(res));
  • window.Store.Wap.lastseenFind("49123456789@c.us").then(res => console.log(res));
  • window.Store.Wap.statusFind("49123456789@c.us").then(res => console.log(res));

Using the amazing Chrome developer console, you can see that window.Store.Wap contains a lot of other very interesting functions. Many of them return JavaScript promises. When you click on the Network tab and then on WS (maybe you need to reload the site first), you can look at all the communication between WhatsApp Web and its servers.

Chat identification

The WhatsApp Web API uses the following formats to identify chats with individual users and groups of multiple users.

  • Chats: [country code][number]@c.us, e.g. 49123456789@c.us when you are from Germany and your phone number is 0123 456789.
  • Groups: [phone number of group creator]-[timestamp of group creation]@g.us, e.g. 49123456789-1509911919@g.us for the group that 49123456789@c.us created on November 5 2017.

WebSocket messages

There are two types of WebSocket messages that are exchanged between server and client. On the one hand, plain JSON that is rather unambiguous (especially for the API calls above), on the other hand encrypted binary messages.

Unfortunately, these binary ones cannot be looked at using the Chrome developer tools. Additionally, the Python backend, that of course also receives these messages, needs to decrypt them, as they contain encrypted data. The section about encryption details discusses how it can be decrypted.

Dealing with E2E media

Encryption

TBD

Decryption

  1. Obtain mediaKey and decode it from Base64 if necessary.
  2. Expand it to 112 bytes using HKDF with type-specific application info (see below). Call this value mediaKeyExpanded.
  3. Split mediaKeyExpanded into:
    • iv: mediaKeyExpanded[:16]
    • cipherKey: mediaKeyExpanded[16:48]
    • macKey: mediaKeyExpanded[48:80]
    • refKey: mediaKeyExpanded[80:] (not used)
  4. Download media data from the url and split it into:
    • file: mediaData[:-10]
    • mac: mediaData[-10:]
  5. Validate media data with HMAC by signing iv + file with macKey using SHA-256. Take in mind that mac is truncated to 10 bytes, so you should compare only the first 10 bytes.
  6. Decrypt file with AES-CBC using cipherKey and iv, and unpad it. Note that this means that your session's keys (i.e. encKey and macKey from the Key generation section) are not necessary to decrypt a media file.

Application info for HKDF

Depending on the media type, the literal strings in the right column are the values for the appInfo parameter from the HKDF function.

Media Type Application Info
IMAGE WhatsApp Image Keys
VIDEO WhatsApp Video Keys
AUDIO WhatsApp Audio Keys
DOCUMENT WhatsApp Document Keys

Extending the web app's capabilities

Adding own commands

The message forwarding procedures are rather complex, as there are several layers of websockes involved in the process. For adding your own commands, follow these steps.

  1. First, decide on what the final destination of your command shall be. To be consistent with the other, please prefix it with backend_ if it's meant to be received by the Python backend or use api_ if the command is directed to the NodeJS API.

  2. Now, look at client/js/main.js. In line 214, you can see an instantiation of the BootstrapStep JavaScript class. It needs the following information:

    • websocket: is probably always the same
    • request.type: should generally be call, as this allows a response to be passed back to the command's sender
    • request.callArgs: an object which has to contain a command attribute specifying the name of your command and as many additional key-value-pairs as you want. All of these will be passed to the receiver.
    • request.successCondition: on receiving a response for a call, this shall be a function returning true when the response is valid/expected. Use the next attribute for specifying code to be executed when the response is valid.
    • request.successActor: when the success condition evaluated to true, this success actor function is called

    When the BootstrapStep object has been constructed, call .run() for running indefinitely or .run(timeout_ms) for failing when no response has been received after a specific timeout. The run function returns a Promise.

  3. Next, edit index.js. It contains a couple of blocks beginning with clientWebsocket.waitForMessage. You can copy one of these blocks and edit the parameters. The waitForMessage function needs the following attributes:

    • condition: when a message is received and this condition evaluates to true on it, the message will be processed by the following .then(...) block
    • keepWhenHit: it is possible for a message handler to be detached immediately after it receives its first fitting message. Control this here. The returned promise's then block finally handles a received message. It gets a clientCallRequest you can call .respond({...}) on to send a JSON response to the caller. If the NodeJS API is not the message's final destination, you need to instantiate a new BootstrapStep here which will contact to the Python backend and, after it receives its response, will return it to the original caller.
  4. Thus, when you want a message for the backend, now edit backend/whatsapp-web-backend.py. In the if-else-compound starting in line 88, add your own branch for the command name you chose. Then, edit backend/whatsapp.py and add a function similar to generateQRCode in line 223. Just using something like in getLoginInfo may not be enough, as your command may require an asynchronous request to the WhatsApp Web servers. In this case, make sure to add an entry to self.messageQueue with the message tag you chose and send an appropriate message to self.activeWs. The servers will respond to your request with a response containing the same tag, thus this is resolved in line 134. Make sure to eventually call pend["callback"]["func"]({...}) with the JSON object containing your response data to resolve the callback.

Tasks

Backend

  • More and more errors start to occur in the binary message decoding. Update this documentation to resemble the changes, then implement them.
  • Allow sending messages as well. Of course JSON is easy, but writing the binary message format needs to start being examined.

Web frontend

  • Allow reusing the session after successful login. Probably normal cookies are best for this. See #9 for details.
  • An UI that is not that technical, but rather starts to emulate the actual WhatsApp Web UI.

General development

  • Allow usage on Windows, i.e. entirely fix #16.

Documentation

  • The Node Handling section. Could become very long.
  • Outsource the different documentation parts into their own files, maybe into the gh-pages branch.

Legal

This code is in no way affiliated with, authorized, maintained, sponsored or endorsed by WhatsApp or any of its affiliates or subsidiaries. This is an independent and unofficial software. Use at your own risk.

Cryptography Notice

This distribution includes cryptographic software. The country in which you currently reside may have restrictions on the import, possession, use, and/or re-export to another country, of encryption software. BEFORE using any encryption software, please check your country's laws, regulations and policies concerning the import, possession, or use, and re-export of encryption software, to see if this is permitted. See http://www.wassenaar.org/ for more information.

The U.S. Government Department of Commerce, Bureau of Industry and Security (BIS), has classified this software as Export Commodity Control Number (ECCN) 5D002.C.1, which includes information security software using or performing cryptographic functions with asymmetric algorithms. The form and manner of this distribution makes it eligible for export under the License Exception ENC Technology Software Unrestricted (TSU) exception (see the BIS Export Administration Regulations, Section 740.13) for both object code and source code.