How WhatsApp enables multi-device capability

https://engineering.fb.com/2021/07/14/security/whatsapp-multi-device/

by mseri • 5 years ago

151 138 5 years ago

engineering.fb.com

senectus1• 5 years ago

WhatsApp uses the Signal encryption subsystem and they only allow one other machine.

What is FB doing that allows this on Whatsapp but not Signal.

What a WhatsApp users opening themselves up for here?

bool3max• 5 years ago

Maybe read the article?

blowski• 5 years ago

HN Guidelines:

Please don't comment on whether someone read an article. "Did you even read the article? It mentions that" can be shortened to "The article mentions that."

ikawe3• 5 years ago

The Signal app never did the "primary device serves message contents to companion devices" like WhatsApp did.

Ever since Signal introduced the desktop client, its multidevice functionality has involved fully fledged signal-protocol sessions between each device.

It sounds like WhatsApp is now adding something like this to their client, though it sounds like some of the details of the scheme differ.

In principal the signal protocol works fine for a multidevice scenario.

david_arcos• 5 years ago

The WhatsApp server maintains a mapping between each person’s account and all their device identities. When someone wants to send a message, they get their device list keys from the server.

Oh, no...

alfongj2• 5 years ago

What's your concern?

Malakun• 5 years ago

But only one phone, yeah...

p4bl0• 5 years ago

Can anyone with good knowledge of the protocol explain the differences between what WhatsApp is rolling out now and what Signal has been doing for a long time now?

fsflover• 5 years ago

Why does it matter if WhatsApp is closed and non-auditable?

Upd. See also:

WhatsApp whitepaper removed sentence about never having access to private keys (twitter.com/shiftreduce)

491 points by Aissen 8 months ago | 106 comments

https://news.ycombinator.com/item?id=25685446

nicce• 5 years ago

Indeed. Signal client at least on Android uses reproducible builds.

ChuckNorris892• 5 years ago

This feature (or lack thereof) is pretty much my biggest gripe against Signal. I still don't understand why they won't let you use the same account in paralel on an Android tablet. And the weird part is they provide no explanation for this limitation while this limitation does not exist for iPad users.

If this new feature proves to work as advertised, I might as well sell my soul to the Facebook devil and go back to WhatsApp full time due to how frictionless the experience is (and everyone in the EU already being on it), and leave Signal only for private info sharing, as I grew tired of convincing people in my circles to move to Signal for privacy only to receive complaints that X,Y, Z features from WhatsApp are either missing, buggy or super frustrating to use on Signal. Oh, and receiving calls on Signal for Android is a mess (known bugs for years) where some calls just won't come through to my phone even if the desktop client is ringing, only to have it show up as a missed call notification on my phone a few minutes later. Unacceptable.

I do support the Signal team for their work and what they stand for, but my patience (and that of those around me I convinced to switch from WhatsApp) is wearing thin.

dannyw2• 5 years ago

Signal's refusal to allow me to export message backups is also unbelievably frustrating.

phaer2• 5 years ago

...on iOS that is? At least on Android, exporting backups seems to work fine (for me).

NilsIRL2• 5 years ago

Signal does have this feature. It's just that their mobile clients do not support it (as a "slave" device), from what I understand this is no different than WhatsApp multi device feature

shawnz3• 5 years ago

This article is regarding a new beta feature in which you can have multiple "host" devices connected to the same WhatsApp account. It's not the same as the previous "WhatsApp Web"/"Signal desktop" experience.

emptysongglass2• 5 years ago

This is why I use Telegram as a "good-enough" alternative to the tech monopolies. No, you don't get E2EE without opting in (and Secret Chats don't exist at all for groups) but it's one of those products that makes joy in the hearts of anyone, enthusiast or no, who uses it. Its clients are fully open-source and the man behind it, Pavel Durov, is truy a hero in my book for his consistent stance against big powers, from state actors to tech giants.

I also selfhost a Matrix homeserver and bridge all-the-things to it, possibly its finest feature but there's no way any of its client implementations is going to spark joy in the hearts of the mainstream.

It's important, much like in our politics, to find the fine line between the extremes so that we can leverage and exploit good-enough choices for more freedom for everyone. I use Linux but for most people it's enough to at least get them to consider some FOSS alternatives in their Windows or macOS environments. We can use these small victories to chip away at the mortar of surveillance.

I will never, ever, return to Facebook products. The global damage wrought by that company will go down in the history books, I'm sure. So let's pick those things that are "good enough" as our chisels for a better future for all.

EDIT: Telegram has a chat export feature if you're a WhatsApp user considering the switch [1].

[1] https://telegram.org/blog/move-history

5e92cb50239222b• 5 years ago

Pavel Durov, is truy a hero in my book for his consistent stance against big powers, from state actors to tech giants.

Oh yeah, especially the recent Smart Voting fiasco. A true hero.

bmarquez2• 5 years ago

I've used the chat export feature of Telegram before deleting my WhatsApp account. It works well and convinced me to use Telegram over Signal in cases where I had contacts on both platforms.

(Personally, I'm also bitter that Signal Android supports backup while Signal iOS doesn't...and transferring from one iOS device to another isn't considered backup).

discobot• 5 years ago

telegram is certainly non a tech-giant with 500M users

trabant00• 5 years ago

This comment proves that convenience trumps security and explains WhatsApp's success.

I also want to note that you can use them in parallel, no need to switch or convince other people to do so.

nindalf2• 5 years ago

convenience trumps security

Your comment implies that security is being traded off in favour of convenience. Could you explain how?

cheschire2• 5 years ago

I'm confused by your post. I use signal seamlessly between my desktop, iphone, and ipad using the same account. I can take photos with my phone, post them to a chat, then go back to my desktop to type longer messages more easily.

Is your problem that a phone is required to be the primary device when doing this?

petemir• 5 years ago

His problem is that he has Android.

ChuckNorris892• 5 years ago

Then you clearly haven't read my post thoroughly. I repeatedly mentioned my issues being with Signal not allowing multiple instances on Android devices using the same account, while you're talking about Signal on Apple devices.

up6w6• 5 years ago

Can anyone explain to me the main obstacles for Signal to succeed ? I keep thinking about how strange is that we can maintain complex open-source projects like linux but we cannot join forces and create a good open-source messaging app, which is a thing almost everyone with a smartphone uses, I know its not the same thing and you need someone to take care of infrastructure etc, but I still think its strange.

MomoXenosaga2• 5 years ago

Because getting to 1 billion users is hard. Google tried it.

Basically people have been using their favourite messaging apps for years now and if they're satisfied they aren't going to switch.

kubanczyk• 5 years ago

Lack of federation. Maybe "we" can maintain some complex free software, but it is them who cannot grow their userbase.

edwnj• 5 years ago

Its very hard to do this without opening up to a lot of potential fuckups and exploits.

The way e2e works is by exchanging public keys (kinda like a cryptographic username), imagine having multiple devices and verifying + keeping track of the keys from each device.

This is why im not surprised fb was the first to come out with this feature, you need fb level resources to get this out first and from a quick look at the article it seems like they're not using centralization to solve the problem.

"WhatsApp multi-device uses a client-fanout approach, where the WhatsApp client sending the message encrypts and transmits it N number of times to N number of different devices — those in the sender and receiver’s device lists."

ignoramous• 5 years ago

Whitepaper: https://web.archive.org/web/20210922105222/https://www.whats...

tasogare• 5 years ago

Crazy that an application is proud, in 2021, to be usable on multiple devices.

hnick• 5 years ago

All that and we still can't use it on 2 phones, or even migrate history between Android/iOS when you change phones.

artiszt2• 5 years ago

for your security, ofc, only for the sake of your security [irony-off]

phaer2• 5 years ago

A feature like that tends to become quite a bit more complicated with e2e encryption and and the kind of (potential) adversaries WhatsApp attracts due to its size.

This would be much easier for an application where all state is stored in clear-text on servers.

And even harder for services which are trying to avoid storing metadata on servers as much as possible, such as Signal.

nicoburns5• 5 years ago

If they're requiring a QR code scan to add new devices (reasonable IMO), couldn't they just use that to sync the encryption keys?

einpoklum• 5 years ago

Let's remind ourselves of a few facts:

Facebook takes part in the US government's mass surveillance operations, granting wide, possibly complete, access to users' communications. This was revealed by whistle-blower Edward Snowden and the documents he had released. Facebook's interaction with the NSA or other government agencies is kept secret, and will not be admitted, so when Facebook tells you your communications via its applications and services are secure, that is certainly not wholly the case, and quite possibly not at all the case.

Additionally, Facebook uses your communications for its own business interests, e.g. to manipulate you into paying for services or products whose providers pay Facebook, or for other kinds of social engineering. It stands to reason that this includes the information Facebook gathers about you from your WhatsApp conversations.

There are other messaging applications with multi-device capabilities - better or worse - and we should strive to use those with open source code, well-established algorithms, and transparent, robust and trustworthy governance as projects.

----

So - please do not use WhatsApp and try to get your friends and family to switch to alternative applications. Signal and Telegram seem to be the popular alternatives, even if they each have their own shortcomings and flaws.

artiszt2• 5 years ago

quite right and this is HN. and one may well wonder in how far FB does NOT seriously interfer with discussions here [and elsewhere, ofc too, for that matter]

nindalf2• 5 years ago

Are you implying that Facebook moderates discussions here? I believe @dang is employed directly by YCombinator and is independent of any other tech company.

As for commenting, I can’t speak for other Facebook employees but I made it a point to never comment on Facebook related discussions while I was still employed there. Frankly I didn’t see the point. Most threads would get so vitriolic and emotional that there wasn’t any space to have a discussion. There would be people spouting conspiracy theories like “Facebook controls discussions on HN”. No real point in engaging in such discussions, I figured.

Gualdrapo• 5 years ago

Can't agree more, it was kind of funny reading they were so worried about "user's privacy" while what you state is now common knowledge.

satyanash• 5 years ago

Signal and Telegram seem to be the popular alternatives

taking your own argument into account, using "popular alternatives" is probably not the right criteria here.

Telegram is not E2E by default, so the name shouldn't even appear in any list of recommendations.

YarickR2• 5 years ago

Don't you think many/most users dgaf about e2e ?

greiskul2• 5 years ago

It stands to reason that this includes the information Facebook gathers about you from your WhatsApp conversations.

It stands to reason that they miraculously break the end to end encryption of Whatsapp?

marderfarker2• 5 years ago

Exfiltration via side channel exists. For instance, Facebook will upload your conversations when you report abuse/block a contact, and this is behaviour they decided to publicise, who knows what else they collect.

nicoburns5• 5 years ago

My phone having recently died, I've recently discovered a number of very annoying limitation to WhatsApp that are making me question my use of it:

1. It's impossible to export your chat history, except for one conversation at a time. The only exception to this is if you root an android phone which gives you access to the raw database.

2. It's impossible to move chat history from an android device to an iOS device. And moving from ios to android is only possible with certain samsung phones.

3. It's impossible to access WhatsApp from more than one phone at once. This is mostly still true with this update. You cannot use the mobile app as a "companion device".

Do people not consider their chat histories valuable? I have my SMS history going back to 2011 (when I first got an android phone). Email can be archived. Facebook messenger keeps messages in perpetuity. WhatsApp is a frustrating outlier here.

illyism• 5 years ago

No, I clear my history from time to time manually. It is very useful at times (to search through) but also not something I want to stick around.

bennyp1012• 5 years ago

"Do people not consider their chat histories valuable?"

Personally, no. I treat it like a real life conversation, if it's something I need to note later on, then I'll make a note of it outside of the chat app

stavros• 5 years ago

I go one step farther and have conversations auto-expire after a certain amount of time (e.g. a week) for both parties. Scripta volent.

mikro2nd• 5 years ago

"Do people not consider their chat histories valuable?"

No, I consider them a positive liability and delete messages/conversations as soon as they're done/actioned.

When the Brown Shirts come to get you, it'll be your own message history they hang you with. (Only slightly :))

Question: You have your SMS history going back a decade. How many times has that proven useful?

I, too, used to keep messages & emails "forever" until I realised that it was doing nothing for me but becoming a maintenance burden. Now I have "max 24 months" retention policy and have never once needed to retrieve an email older than that.

alksjdalkj• 5 years ago

When the Brown Shirts come to get you, it'll be your own message history they hang you with. (Only slightly :))

There are certainly some countries where this isn't a hyperbole. But in all others, suggesting that Nazis might come take you away because of messages you've written in the past is in pretty bad taste, IMO.

intricatedetail• 5 years ago

No, I consider them a positive liability and delete messages/conversations as soon as they're done/actioned.

Does other side delete it too? Otherwise if you delete you create a bigger liability in case the other side start claiming things that have not happened. For that reason it's vital to keep an audit trail and of course you need to have good op sec with that.

bobsil1• 5 years ago

I save love letters / emails / texts, tax docs

All else, purge every year

rimliu• 5 years ago

Same. After reading the first point my reaction was "Why would I want that?" Of course, people are different, but I think in digital world there are much more hoarders than in physical.

j3th9n2• 5 years ago

To answer your question: I don't value chat histories that much. In the early days people didn't walk around with tape recorders to record everything everybody was saying either. If there is something really important said in a chat, you could make a screenshot, the same way you would take a note on paper with a pencil in pre-digital times, but how often did that happen? To write down an address for example, but you could put that in the digital equivalent of the rolodex, like Contacts.app or Notes. You could even go as far as to save information in a personal CRM like Monica.

nicoburns5• 5 years ago

People did used to write each other letters though, which they would often keep. I definitely have some correspondence over chat that falls in that category. Perhaps I should go back to writing such messages on physical media.

sharikous• 5 years ago

You can transfer your chat history if you back it up on Google Drive and pull it from the new device.

I suppose you don't want to do that, maybe because it gives a third party access to your history (although it should be E2EE), but I am writing this for readers who may stumble upon this

shawabawa3• 5 years ago

iOS don't let you backup or restore from google drive, only iCloud

Android only let you use google drive. There's no way to transfer between the two

er4hn2• 5 years ago

A lot of the replies I see to this are people talking about their personal chat histories. For various reasons the trend these days is to not consider those valuable*

Where chat histories are valuable and where you see a "store and index it all" approach is enterprise chat. Slack, Google Hangouts Chat, etc, store and archive all the data because that is the collective wisdom of past and present employees and it is valuable to search through. Depending on the industry (i.e. Finance requires this via FINRA) it may even be mandatory to record all communications.

* unless you are moving to a new device, but even then it is rare to search that far back in history.

torben-friis• 5 years ago

2. It's impossible to move chat history from an android device to an iOS device. And moving from ios to android is only possible with certain samsung phones.

It is possible to do this with third party apps. Incredibly sketchy looking apps I should add, but they do work. I've done it several times both ways.

sizzle2• 5 years ago

Same I paid $20 for some software recommended on Reddit. No clue what it did or exploited but it transferred everything including media from android —> iOS. Best $20 I ever spent, had a lot of chats with info I search for periodically.

MomoXenosaga2• 5 years ago

Moving from Android to iOS and vice versa has been a nightmare since forever and I don't blame WhatsApp for that.

nicoburns5• 5 years ago

Pretty much everything else has transferred over very smoothly for me so far. My passwords are all in Bitwarden so I had instant access to those. And my contacts are all in Google Contacts which transferred similarly easily. I've had to log in to a lot of apps, but other than that it's been pretty easy apart from whatsapp.

gorgoiler• 5 years ago

I’ve not looked, but is there no GDPR style “download your data” tool?

I used that effectively to keep long term archives of all my Facebook conversations. Critical for remembering what happened when and cat photos.

ajvs3• 5 years ago

Conversations are E2EE encrypted so their tool doesn't work for those.

tinus_hn3• 5 years ago

WhatsApp on iOS does backup all history, allowing you to transfer it to a new iOS device.

Transferring history between iOS and Android is a work in progress, it works now from iPhone to Samsung devices (for reasons I don’t really understand), general support is supposed to be rolled out the coming months.

miohtama• 5 years ago

This is ok, but competing apps like Telegram had had this for ages. Hopefully the best app wins and capitalism does its trick.

kelnos• 5 years ago

I also consider my chat history valuable. Is there a reason why you don't use WhatsApp's built-in backup mechanism? On Android it backs up to Google Drive, I believe. But yeah, moving history backups between Android and iOS isn't possible, which is pretty lame.

ajvs3• 5 years ago

1) It seems the raw databases are encrypted in `/storage/emulated/0/Android/media/com.whatsapp/WhatsApp/Databases` so even being rooted isn't sufficient to dump them.

sizzle2• 5 years ago

I paid $20 for some software reviewed on Reddit I found searching “transfer WhatsApp messages from android to iOS”, no root needed. It somehow transferred everything including media, like magic. It’s a black box and who knows what exploits they are using in the background, but just wanted to chime in and let you know it’s possible but not out of the box.

If anyone is interested, I can dig up and share the software/company I purchased from.

rd07• 5 years ago

End-to-end encryption on multi-device? I think Matrix and Element solved this before.

heeen2• 5 years ago

verifying between all parties involved is incredibly clunky though

vurpo• 5 years ago

Getting the full benefits of E2EE (that is, protection against active attacks and not only passive eavesdropping) requires verification out-of-band in any case. Verifying is entirely optional on both Matrix and WhatsApp (not verifying doesn't affect the functionality of the chat), but gives you the same benefit on both platforms.

But then again, WhatsApp actively hides the feature away behind menus and pretends it's not really a thing, while Element is a bit more pushy about telling you about it.

bennyp1012• 5 years ago

Hopefully this will make using the WhatsApp bridge on Matrix much easier - one of the reasons I haven't gone all in on Matrix. If I can have a device setup that is linked, then I don't have to run a VM or (hopefully) have it even installed on my phone.

2T1Qka0rEiPr• 5 years ago

Perhaps this is an odd question - but can someone comment on why this was posted today? The blog post is from July, so I'm wondering whether it's past the initial experimentation phase or something?

rPlayer6554• 5 years ago

WhatsApp only just recently told me this was a feature. So yea I assume it was only fully rolled out around now.

vdfs• 5 years ago

Still in Beta, I've been using it for ~3 weeks

londons_explore• 5 years ago

With more and more services going e2e encrypted, the application servers no longer have any special role or logic. All data they store is no longer privacy or security critical, and they no longer need ACL's.

I'd therefore like to see future chat services like this to just have one big S3 backend (or similar).

SMAAART• 5 years ago

It has been a while.

Also now, when a conversation is archived it remains archived even if someone in that group posts something. Before when someone in an archived conversation posted something the conversation would be unarchived.

gregoriol• 5 years ago

Does anyone with knowledge on the subject know how different it is from what Matrix/Element does? or any other implementation?

nicoco4• 5 years ago

ctrl+F "XMPP"… No? OKay, I'll be that guy.

Multiple devices, multiple platforms, E2EE, gateways to other networks... my XMPP server handles all of that, and I convinced non-tech users to use it mainly because of the great Android client Conversations.

Yes, there are some rough edges because there isn't a iOS client that matches Conversations in terms of user friendliness. But siskin-im in on its way there.

I also have had complaints from friends but mainly because I am a shitty admin...

Oh, and having your phone number as your username is something that really is important for you? Use Quicksy then.

dmitriid3• 5 years ago

and I convinced non-tech users to use it mainly because of the great Android client Conversations.

And that's the only client in existence that supports the XEPs required for XMPP to be a viable alternative in the modern world.

What about iOS? What about desktop?

I also have had complaints from friends but mainly because I am a shitty admin

What if I don't want to run my own XMPP server? How do I find the one that supports message carbons, file uploads, encryption, push notification, client state indications...

MattJ1002• 5 years ago

And that's the only client in existence that supports the XEPs required for XMPP to be a viable alternative in the modern world.

That's not true, but admittedly that information is not trivial to find right now for end users. It's a known problem, and people are working on a nice comparison of XMPP client capabilities so people can make a more informed choice.

What if I don't want to run my own XMPP server? How do I find the one that supports message carbons, file uploads, encryption, push notification, client state indications...

https://compliance.conversations.im/ or for something less overwhelming, https://joinjabber.org/

nicoco4• 5 years ago

What about iOS?

Siskin [1] seems to be the best client for iOS right now. It's not as good as Conversations.

What about desktop?

I am pretty happy with beagle (OSX) [2], Dino (Linux) [3] and Gajim (linux, windows, OSX) [4]. If in-browser is your thing, converse.js [5] or movim [6] come to mind.

What if I don't want to run my own XMPP server?

Use quicksy.im?

[1] https://siskin.im

[2] https://beagle.im

[3] https://dino.im

[4] https://gajim.org

[5] https://conversejs.org/

[6] https://movim.eu/

f1refly3• 5 years ago

While I'm with you on xmpp, calling Conversations "great" is dishonest. While the foundation is good and the xep support is great, the developer refuses to adapt the client to any conventional design standard, requiring the users to use either blabber or monocles to achieve some familarity. Besides that, message search is not able to link the message into context, while showing both timestamp and associated chat, requiring the user to go into the chat himself and scroll up until the message in question shows up.

nicoco4• 5 years ago

I never use the search feature, so I believe you if you think it's bad.

What are blabber's or monocles' selling points compared to Conversations? I couldn't find with a quick search, but I'm open to suggesting them instead of Conversations if their UI is better.

gefhfff• 5 years ago

Multiple devices... without sync

Multiple platforms... but iOS a night mare with E2EE

Gateways to other networks... Honestly I couldn't find working ones

Why would you want to make a phone number your user ame - this way you are sharing it with almost everyone...

nicoco4• 5 years ago

without sync

My message history in sync'ed between Conversations (Android), Dino (Linux), Gajim (also Linux) and beagle-im (Mac OS X). Not sure what you are referring to.

Gateways to other networks... Honestly I couldn't find working ones

Anything supported by pidgin can be used as a gateway through spectrum2. I use telegram and mattermost this way. I admit that spectrum2 is a bit confusing to set up, but it works!

Why would you want to make a phone number your user ame - this way you are sharing it with almost everyone...

I am with you on this! But to many non tech user, this seems to be important. Some get the feeling that they don't "create an account" when they use whatsapp or similar.

saurik• 5 years ago

With this new capability, you can now use WhatsApp on your phone and up to four other nonphone devices simultaneously — even if your phone battery is dead.

Does "non-phone" here at least include "iPad"? The use case of "if your phone battery is dead" is just such a non-issue for me, as I have a million other critical reasons to keep my phone charged and online... but having the WhatsApp external client--the one you install on laptops--available for iPads and even other phones would actually open up new use cases for me.

RMPR• 5 years ago

That's an interesting and long awaited update. But there's no mention of a new desktop app, or new web app. I wonder how users in the beta will be able to test this.

Aardwolf• 5 years ago

I could run chat programs on multiple computers in the 90s, so today we're in a worse state than then. What gives?

skymt• 5 years ago

Did those chat programs encrypt messages end-to-end while syncing message history across devices?

tinus_hn3• 5 years ago

With no encryption so the network, the servers and basically anyone who cares to look can see your private messages. If you don’t care about that, indeed it’s easy to implement things.

er4hn2• 5 years ago

Something that is interesting here is on-boarding new devices. Since all the encryption is done by each message being sent to the {all sender devices (M), all receiver devices (N)} you end up with M+N encryptions.

When onboarding a new device, it needs some amount of state in order for conversations to have a useful context. So the new sender device gets a bundle of recent conversations from who-ever onboarding it. I'm not clear on how you could control the amount of context or add more state, but that is off-topic.

What I'm wondering is: Does this have a race condition? Say that you have:

Sender A knows about receivers {B,C,D} Sender A sends message Foo to {B,C,D} Receiver E is onboarded at the same time Foo is sent. Is there no state where E does not receive the message?

I'm sure that this is accounted for and out of scope in a high level blog post, but I am curious how that part works.

greggman3• 5 years ago

Now if they'd just stop the spam and get rid of the phone numbers! There is ZERO good reason to require a phone number in 2021 nor to access my contact list of which the majority fo the people I talk do I don't have their number.

throwawaybutwhy• 5 years ago

The ship has sailed. While we endure incessant 'we want you to bend backwards and agree to our new TOS' in WhatsApp, Telegram keeps being friggin' awesome and getting better every fortnight or so.

baby2• 5 years ago

isn't Telegram unencrypted?

AlexanderTheGr8• 5 years ago

by default. But you can change it to encrypted in settings.

It would be nice if it was the other way around - encrypted by default and unencrypted using settings

Apofis• 5 years ago

Smells of NSA.

jwogrady• 5 years ago

Don't worry, we will store those keys nice and safe.... In case we get subpoenaed. Just scan you retina.

How WhatsApp enables multi-device capability

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