Rust at Scale: An Added Layer of Security for WhatsApp
(engineering.fb.com)264 points by ubj 4 days ago
264 points by ubj 4 days ago
Did they say anywhere what they did? Rebuilding the stdlib as part of your build can shrink it a lot depending on how much of it you use, but that is still nightly only. Maybe they went no_std or created their own?
They didn't but keep in mind that the app is currently 170MiB. The standard library shouldn't have added more than a few hundred kilobytes. They already likely pay similar costs for c++, but it's more worthwhile as they have a lot more c++ code total.
Also note that if you statically link to the rust std library, lto will excise the majority of it anyways, no need to rebuild it.
The default hello world stripped with one codegen unit and panic=abort was 342kB both nightly and stable. Adding lto dropped it 42kB in stable and 40kB in nightly. Adding build-std and only building core did not reduce it any further in size.
> We believe that this is the largest rollout globally of any library written in Rust.
I think that crown currently goes to https://github.com/googlefonts/fontations which is included in Chromium, not sure if it's on all platforms yet. Moreover, the translative dependencies of Fontations (click through https://crates.io/crates/fontations/0.3.0/dependencies) should have an even (slightly) larger install-base.
EDIT: from the quote you can also gather that they don't use https://github.com/signalapp/libsignal
Just a few more Rust libraries we've shipped in Chromium:
- https://github.com/image-rs/image-png
- https://github.com/webmproject/CrabbyAvif
> over 3 billion people to message securely each and every day.
Whatsapp is a chat application with 3 billion daily active users.
For those of you in the US (where Whatsapp is seldom used), this is a fact worth remembering.
If you want to build products for the rest of the world, you need to know how those users think and breathe - and for 3 billion of them, Whatsapp is how they talk.
What one should do about this? I mean, beside working on lowering that number.
(Asking as a European who quite stubbornly refuses to install it - there are dozens of us. Dozens!)
Edit: please don't participate in making WhatsApp even more inescapable as it is today.
As a developer, I tried building an app that needs to use Whatsapp for communication. Unfortunately my phone number got blocked by the second test message. No Spam. Not marketing, just a test message to my own number. Along with it, they blocked my entire business, my LLC, and anything tied to it.
I have been trying to get hold of anyone or anything at Whatsapp. I've spent 6 months trying to navigate the bureaucracy. Facebook support claims they can't touch WhatsApp; WhatsApp support ignores the Facebook side. If you're building on WA, have a backup plan.
If any Whatsapp employee reading this can look into my WBA Account 1117362643780814
The number is only checked at login, and after that you can now create a WebAuthn passkey (iCloud Keychain/Google Passwords synced to your next phone) for future sign-ins so it's actually only needed for first sign up. So just get a prepaid SIM or eSIM and make another account unless your business is so large that tons of people know your number.
Sorry I am confused. I have a "WhatsApp Business Account", tied to an "Business" (verifications all done). What I am talking about is registering a phone number that acts as the "Sender/Responder" of the messages from my customers. I am not trying to use WhatsApp from my phone manually, but have my app communicate with my customers programatically. Hope this is clear.
I can't do any of the above,
1. Requesting a new test number. Test numbers are placeholder 555 number that works only within WhatsApp test network. Can't get one.
2. Registering a new, real phone number (SIM obtained from a regular tele provider)
3. Disconnecting the WhatsApp product from the Facebook App to reset the integration.
Although the FB app is being used, I don't have any WhatsAppp users (because I have not even made the product), so wiping out any WBA accounts and starting fresh is also okay, if someone can do this.
You're supposed to go to a local WhatsApp partner instead of contacting WhatsApp directly if you want to get API access for sending messages.
I guess if you want to lower that number, you'd need to build something better, in some way. Answered as another European who've had Whatsapp forever, as some stubborn people refuse to move away from it, and also bunch of businesses use it.
Network effect is killer. "better" would include having more than 3 billion people already on it.
Maybe the EU or China will crack down on it. A single company shouldn't decide who gets to talk to half the world. If that company is American they will not tolerate it for long.
Personally DeltaChat is my new favorite Thing but it falls afoul of Zooko's Triangle - A WhatsApp number or POTS number is short because it's centrally controlled and you have to pay for each one. DeltaChat has public keys, so I have 20 of them, and nobody can control who gets one, but they're incredibly long... the QR codes are nightmares.
Make your customer support on whatsapp. "Drop us a message to change your order". Allow ordering/enquiries over whatsapp.
Send 2 factor verification pins over whatsapp - it is more reliable than SMS and generally there is a better 1:1 mapping between whatsapp accounts and real humans than phone numbers, so it is a good anti-spam or good way to distribute "first month free" type deals whilst keeping abuse low.
Obviously make sure all URL's have info cards properly rendered in Whatsapp for good share-ability.
Force interoperability one way or another. WhatsApp is a closed system, if I want to use an alternative I'm stuck with adversarial interoperability, so stuff like Beeper (which is great, but...) which might get my account banned. Or waiting for some legislation to force WhatsApp to open it's API and let me interact with my contacts there without being locked into their apps
There is legislation in the EU, and BirdyChat announced compatibility.
https://www.birdy.chat/blog/first-to-interoperate-with-whats...
> What one should do about this? I mean, beside working on lowering that number.
Every business in Brazil has an whatsapp to talk to their clients. Sometimes this whatsapp goes into the phone or computer of a real human being. Other times, it's manned by a bot (usually a dumb choose-your-own-adventure bot - I don't see business using LLMs for this here)
Indeed I use food delivery apps (ifood here) only to check out the menu of delivery restaurants, then I search for them in Google so I can order directly from them through whatsapp. This won't work for some dark kitchens, but other than that it's pretty reliable and avoid the middleman
Well, you now have the right to use third-party apps to exchange messages with WhatsApp users, but apparently your law only covers it if the other user is in the EEA. So you are back to square one when communicating with India, Pakistan, and much of SE Asia, Africa, and MENA.
Can you describe your reasons? I haven't developed an opinion as no one here uses it.
I refuse to use proprietary software as much as I can, especially when it has a strong network effect where it encourages others to join.
Meta is also a despicable company, they don't need my help to succeed.
(edit: and I haven't abandoned the idea to switch back to a Linux mobile OS at some point, and WhatsApp would be a pain)
Where I come from (Malawi, Africa), WhatsApp is so widespread that most people prefer it over email - to the extent that people don't really check their e-mails unless it's required for work or they are applying for something. For most people, WhatsApp is the de-facto communication channel.
I help moderate a community of developers and we hit the whatsapp group limit of 1024 members and sometimes have to wait for someone to leave (intentionally or accidentally) before we can add new members. We've tried to move people onto "better" platforms like Discord or Slack but we always end up coming back to WhatsApp which is subsidized via MNOs (mobile network operators) social media data/internet bundles and for the fact that most people are just stuck on whatsapp.
Yeah and we know it is over 3 billion because security researchers from the university of Vienna could read that in one go from one source ip address without encountering any rate limiting:
"phone number, public keys, timestamps, and, if set to public, about text and profile picture. From these data points, the researchers were able to extract additional information, which allowed them to infer a user's operating system, account age, as well as the number of linked companion devices."
See: https://www.univie.ac.at/en/news/press-room/press-releases/d...
In markets where Whatsapp is entrenched, it’s already begun to enshittify.
They have ads and spam already (sorry, no-consent messages from businesses). This isn’t even new. [0]
There’s a clear pattern, say “we’ve rolled out strict policies”[1] and then… nothing changes on the ground, and TechCrunch writes another “they’ve fixed it” article a year later.[2]
Also their Communities feature has pretty crap UX.
Yes WhatsApp’s pervasive. But if pervasive was the end of the story, we’d all be using ICQ and AOL. The last thing any country needs is to hand over more of their lives to Facebook [sic].
[0] https://techcrunch.com/2022/10/10/in-india-businesses-are-in...
[1] https://techcrunch.com/2024/11/20/whatsapp-will-finally-let-...
[2] https://techcrunch.com/2025/10/17/whatsapp-will-curb-the-num...
Honestly? That claim seems a bit(read A LOT) exaggerated. I haven't had whatsapp in a decade and none of my friends(scattered all over Europe) or family uses it. Viber used to be a big deal and to an extent still is in some areas of Europe. Personally I think I've talked almost everyone into migrating to Signal.
No one I know in the UK seriously uses signal. If I'm asking for a phone number from a neighbour it's going to be WhatsApp
Doesn't this description describe Facebook itself? Should we make apps more like that as well? Because they could not be more polar opposite each other.
The hardest part of a rewrite like this is usually maintaining bug-for-bug compatibility with the legacy parser rather than the actual Rust implementation. Most real-world media files are malformed in some way that the C++ code implicitly handled, so if you write a strict parser you end up breaking valid user data. Differential fuzzing seems like the only practical way to map that behavior without manually reviewing millions of edge cases.
I suspect it is actually about maintaining permissiveness for malformed inputs rather than keeping security bugs. I ran into this building ingestion for a print-on-demand service where users upload technically broken PDFs that legacy viewers handle fine. If the new parser is stricter than the old one you end up rejecting files that used to work, which is a non-starter for the product.
Not AI. Anyway, the real issue is permissiveness vs strict parsing—real-world files are messy.
> We believe that this is the largest rollout globally of any library written in Rust.
I suppose this is true because there's more phones using WhatsApp than there are say Windows 11 PCs.
Given that WhatsApp uses libsignal, is it safe to assume that they haven't been using the Rust library directly?
WhatsApp doesn't use libsignal, and Android is already pretty Rusty and deployed more than WhatsApp around the world (not just smartphone. Tons of "embedded" use cases also run on custom Android)
>deployed more than WhatsApp
If you count old Android versions before Rust was added.
Like our gym devices that have a full tablet to run a basic application to control weights, talk about wasting money.
It doesn't make sense for that device alone, but the vendor probably supplies all the different equipment in the gym. Using a tablet simplifies their supply chain, deployment, debugging/repair, app update process and simply supports more features. There are probably some connectivity features on the device, for example. When you look at all of that together, it's hard to argue it's wasting money.
It's like complaining about Electron apps. For sure I love small native apps like everyone else. But, if Electron enables a company to ship cross-platform apps and iterate faster, who am I to say no?
(I happen to have seen some of those tablets in diagnostic mode and poked around a bit. These things are much more complicated than you think.)
If you watch "Microsoft is Getting Rusty: A Review of Successes and Challenges" it appears the whole effort is more on the Azure side, and besides some timid adoption like GDI regions, there is a lukewarm adoption of Rust on Windows side, still pretty much a C and C++ feud.
> Two major hurdles were the initial binary size increase due to bringing in the Rust standard library [...].
They don't say what they did about it, do they? Did they just accept it?
I suspect they just use no_std whenever its applicable
https://github.com/facebook/buck2/commit/4a1ccdd36e0de0b69ee...
https://github.com/facebook/buck2/commit/bee72b29bc9b67b59ba...
Turn out if you have strong control over the compiler and linker instrumentations, there are a lot of ways to optimize binary size
Probably yes. It's ~300KB per binary, and it's a one-time cost.
It can be avoided entirely by disabling the standard library, but that's inconvenient, and usually done only when writing for embedded devices.
Usually the problem isn't the size directly, but duplication of Rust dependencies in mixed C++/Rust codebases.
If you end up with a sandwich of build systems (when you have library dependencies like C++ => Rust => C++ => Rust), each Rust/Cargo build bundles its copy of libstd and crates. Then you need to either ensure that the linker can clean that up, or use something like Bazel instead of Cargo to make it see both Rust and C++ deps as part of a single dependency tree.
Posted elsewhere but The default hello world stripped with one codegen unit and panic=abort was 342kB both nightly and stable. Adding lto dropped it 42kB in stable and 40kB in nightly. Adding build-std and only building core did not reduce it any further in size.
Can it do lto on stdlib even without the nightly build-std flag?
I mean you get one upfront cost for things like allocators, common string manipulation and std::fmt, std::{fs, io, path} helper functions, and gathering of pretty backtraces for panics (which is a surprisingly fiddly task, including ELF+DWARF parsers and gzip to decompress the debug info).
A println!("hello world") happens to pull in almost all of it (it panics if stdout is closed).
Later code growth is just obviously proportional to what you're doing, and you're not getting a whole new copy of std::fmt every time you call print.
We invested a lot into build system optimizations to bring this number down over time, although we did accept on the order of 200 KiB size overhead initially for the stdlib. We initially launched using a Gradle + CMake + Cargo with static linking of the stdlib and some basic linker optimizations. Transitioning WhatsApp Android to Buck2 has helped tremendously to bring the size down, for instance by improving LTO and getting the latest clang toolchain optimizations. Buck2 also hugely improved build times.
Who knows what they did, but there are things which can be done: https://github.com/johnthagen/min-sized-rust
> "WhatsApp provides default end-to-end encryption for over 3 billion people".
Wasn't there news lately that they can still read your messages somehow?
I don't trust un-auditable client applications...
If you want to assure me your e2e is secure, there must be at least two clients implemented by different people, with at least one of them opensource.
Whatsapp used to have this, but lately they have cracked down on third party clients.
> Whatsapp used to have this, but lately they have cracked down on third party clients.
Blame spammers on that. The amount of scammers and spammers on Whatsapp is unreal.
If there is a 2nd opensource client written by someone else, you would hope they would raise the alarm when asked to implement "feature flag 437 means send all the crypto keys to the server".
Every encryption is end to end if you're not picky about the ends, or metadata.
Do you trust facebook (excuse me, meta) to not snoop on your messages, and to not share them with the "intelligence" agencies ?
This is not true. The IETF draft is explicit that E2EE means that the message cannot be read by any party other than the sender and the intended receiver. When companies like Meta claim they support E2EE, this is what they claim. There are no tricky semantics or legalese at play here.
Speaking of Zoom and encryption, its crazy that they bought Keybase (I think they basically said it was largely an acquihire) years ago, and have neither shut it down as everyone thought, nor materially changed it in any way. Unless they changed something it even gives 200GB cloud storage (KBFS) iirc.
It's not entirely accurate to say "any party other than the sender and the intended receiver," since the messaging app running on the user's device can read the messages. Something like "any third party (other than the app vendor)" would be more accurate. Without actually analyze app behavior, it comes down to trusting that the vendor doesn't do anything nefarious.
> When companies like Meta claim they support E2EE, this is what they claim.
Well, that statement can only resolve to true.
These requests of data collection are perfectly legal. FBI DITU gives an order: give me all chats from *@banana.com and they receive banana.com.
From there, two choices from the perspective of a tech provider:
a) You accept. You get paid.
You can always claim you had been coerced / are a victim, and that everything has been done by the law.
You take the risk to lose over 250K per day (!) in fines, some other court scandals that will come to you, some shady private stuff (what if we learn about your secret jacuzzi ?), harassement of the team, be publicly shamed that you supported terrorists who caused actual death of Americans, etc.
In addition, nobody will know that you are the privacy hero and you are not even sure that the data is not exfiltrated another way.
Yes, we looked carefully and decided we won't enjoy losing 100M USD and go to jail.
The trick is that the identifier / wildcard can be very vague and wide. Or there can be multiple of them, each of them are narrow, but put one of top of the other they are super wide.
> Do you trust facebook (excuse me, meta) to not snoop on your messages
No, but I trust some nosy German guy at TU Whatever to spend hours poking at the assembly, find that hidden flag and proudly present it at 40C3.
With enough eyeballs, all source is open (and AI will give us far more eyeballs than we have any idea what to do with).
Sure, you can have different builds distributed to different people, but the NSA can also just do that with Signal, Signal being open source makes it that much easier. FDroid mitigates this somewhat, but it's not like the NSA can't get a fake TLS certificate for their domain and MITM your communications.
I love how Meta will do anything but prevent phishing and prepaid credit card scams in Whatsapp/Messenger
Just like Google’s Rust-in-Android blogs this reads like a PR piece (and in the case of facebook also recruitment piece) with some technical words sprinkled in for effect. The overall communication quality is that of a random startup’s “look what we did” posts.
The interesting aspects, such as how they protect against supply-chain attacks from the dependency-happy rust toolchain or how they integrated the C++ code with the Rust code on so many platforms - a top challenge as they said - remain a mystery.
Would also be interesting to hear how much AI-driven development they used for this project. My hope’s that AI gets really good at Rust so one doesn’t have to directly interact with the unergonomic syntax.
The point of articles like this is to help build credibility for rust adoption. Rust is still not very widely adopted industry wide, and a lot of smaller players only use established technologies that bigger firms have shown works well. Rust is not inevitable, and articles like this are necessary for its future industry adoption.
PR makes it sound like it only benefits the company. It benefits the broader rust community as well. Where was it established that the article must provide you some technical knowledge to learn? I sure didn't go into reading it with the expectation it would.
> The interesting aspects, such as how they protect against supply-chain attacks
There are standard techniques to help manage this that apply across languages, there's no reason to reinvent that wheel.
> My hope’s that AI gets really good at Rust so one doesn’t have to directly interact with the unergonomic syntax.
"Unergonomic syntax" is the battle cry of many people resisting learning a new language. AIs have progressed far enough that they can help you in that learning process, though.
The dependency management and complexity/poor ergonomics are the two major technical problems with Rust. Normally the first one’s ignored while the second is downplayed, so it would have been interesting to see what (if anything) Facebook have done about them.
Not only can AIs help, but they can write most if not all the code and spare the human from learning all the intricacies of individual programming languages. Problem is, reports are contradictory on compatibility with Rust. We know they work great with simpler/friendlier languages like Go or Python.
Quite impressive, I did not know so many bugs were due to memory access.
To be fair the increased reliability of Rust code over C++ isn't just because of memory errors (out-of-bounds accesses, use-after-free, type confusion, etc). You also get:
* No undefined behaviour (outside `unsafe`, which is quite easy to avoid). In C++ there are many many sources of UB that aren't really memory errors directly, e.g. signed integer overflow or forgetting to `return` from a function.
* A much stronger type system.
Those two things have a really significant impact on reliability.
Rust's "A language empowering everyone..." tagline also helps justify the heavy lifting needed to prevent you shooting yourself in the foot, because we're all able to imagine a hypothetical less experienced programmer who might make a mistake even as we swear that we'd never make it ourselves.
Cool - now we only need to get selling-you-out-for-profit-Zuckerberg out of WhatsApp to make it really trustworthy.
That's right, Signal (https://kerkour.com/signal-app-rust), Proton (https://kerkour.com/proton-apps-rust), Matrix, Wire and many more are using a share, cross-platform Rust core and a platform-dependent UI layer.
But it's not only the security-critical paths, but also most of the business logic (see the 2 posts above).
I agree with everything you say. But wow, does that comment sound like AI. Probably Grok?
Not saying you are AI, you might just be a heavy user who picked up the same patterns
If it were an old account I might have given them the benefit of the doubt, but they literally just joined to make this comment. There's so many green accounts popping up which reek of AI now, like I've seen ones where all of their comments are almost exactly the same length.
It's a brand new account that reads 100% like a ChatGPT response where the author just swapped out the em dashes for hyphens when posting, knowing it's a common "indicator" people look for.
It's more surprising to me that it seems to have already fooled a bunch of people looking at their replies to you.
The "is key - ", is a key giveaway.
EDIT to expand the evidence: It's placing unnecessary emphasis on a one off mention in the article (differential fuzzing) and then writes a bunch of bullshit around what it thinks it means (it's wrong, differential fuzzing isn't running them both in parallel during a transition, it's a testing methodology based on inputs/outputs).
Oh come on, that was funny. It also highlights a problem with the way people write rust. If your app panics it has a bug. People throw panics in cases that can absolutely happen, a file isn't there or fails to parse, some set of inputs is mutually inconsistent these are things for error checking. Even if the correct way to handle an error you detect is to stop the app, do that instead of panicking. Panics are for things that should be impossible. Ideally they even get optimized out.
The differential fuzzing approach is clever — way safer than a big-bang rewrite. Running both versions in parallel to catch edge cases before switching over is how you actually ship rewrites without breaking production. The 160k to 90k LOC drop is impressive, but the real engineering win is the validation strategy.
On binary size, static linking with LTO should handle most of the bloat without needing custom stdlib builds.
A comment like this works as well, let the community do its thing.
There are a couple of bots here.
Quoting a user:
keeping it simple: a flat $15,000 to get you on the front page of Hacker News.
[...] contact e-mail below
Spend a week to do a bot, get 10'000 USD of ARR for your B2B tech SaaS, and applause from your investors.
And a week is probably exaggerated, 2 days max
Do you have any actual evidence that these types of services are being offered for that type of price point, though?
The reason I'm asking is that I actually believe the price point is much lower. It's probably much easier to get on the front page of HN of you time the submission + upvotes well enough.
The 160k → 90k LOC reduction is nice, but the parallel rollout is the more interesting part. Running Rust alongside the C++ version and using differential fuzzing to check equivalence is a lot more realistic than “rewrite and pray.” You get incremental validation with the old system as a fallback. Curious how long they ran both before cutting over.
Binary size is a real concern on the client side. On servers the Rust stdlib overhead usually doesn’t matter, but when you’re shipping to billions of mobile devices, every KB counts. Good to see they invested in build tooling instead of just accepting the bloat.