Is Proton Drive Really Zero-Knowledge? An Honest, In-Depth Answer (2026)

Short answer: yes, mostly, and that already puts Proton Drive in a tiny minority of cloud storage services. Proton Drive is genuinely end-to-end encrypted by default, on the free tier too, and Proton's servers really cannot read your file contents, your file names, or your folder structure. That is the real, verifiable meaning of zero-knowledge, and Proton delivers it honestly. But 'zero-knowledge' is not a binary badge. Proton still sees metadata like file sizes and timestamps, the browser version relies on JavaScript that Proton itself serves to you every session, and an academic security analysis found weaknesses in how integrity checks were enforced. So the accurate answer is: Proton Drive is one of the few cloud services where zero-knowledge is real rather than marketing, with a handful of caveats worth understanding before you trust it with everything.

I build an encrypted workspace called Filarr, so I spend an unreasonable amount of my life reading other people's cryptography whitepapers. That means I have skin in this game, and I am going to be upfront about it: Filarr and Proton Drive are not the same kind of product, and for a lot of people Proton Drive is the correct answer. I am not here to tell you otherwise. What I am here to do is take the phrase 'zero-knowledge' seriously, because it gets thrown around so loosely that it has almost stopped meaning anything, and Proton Drive is one of the rare products that actually earns most of it.

The reason the question matters right now is that the cloud storage market has quietly split into two universes that look identical from the outside. On one side you have Google Drive, Dropbox, OneDrive, and iCloud, which encrypt your files at rest and in transit but hold the keys, which means they can read your documents, index them, scan them, hand them to a government, or leak them in a breach as plain readable files. On the other side you have a small cluster of services that promise the server literally cannot read your data. Proton Drive is the most famous name in that second universe, and it has grown fast enough that 'is it actually private, or is that just marketing' has become a genuinely common question. People have been burned before. MEGA promised zero-knowledge and researchers found serious flaws. Everyone remembers the services that said 'military-grade encryption' and turned out to hold a master key the whole time.

So let me walk through the whole thing properly. What zero-knowledge means, what Proton Drive actually does under the hood, where the phrase holds up and where it gets fuzzy, and then, because I would be lying if I pretended I did not have an opinion, how a local-first workspace like Filarr answers the same underlying worry from a completely different direction. If all you want is a private place to sync files across your laptop and phone, you may finish this article and go install Proton Drive, and that would be a perfectly good outcome. If what you actually want is for your data to never leave your own disk in a form anyone else controls, you might finish it wanting something else. Both of those are correct answers to different questions.

What zero-knowledge actually means, precisely

Before we can judge whether Proton Drive is 'really' zero-knowledge, we need to nail down what the term is supposed to guarantee, because the confusion in this whole category comes from people using three different words as if they were synonyms. Encrypted at rest means the provider scrambles your data on their disks but keeps the keys, so it protects you against a stolen hard drive in their datacenter and against nothing else, because the provider can decrypt at will. End-to-end encrypted means the data is encrypted on your device and only decrypted on your other devices, so the ciphertext that travels and sits on the server cannot be read by the server. Zero-knowledge is the architectural promise that the service provider has designed itself so that it never possesses the keys in the first place, cannot derive them, and therefore genuinely cannot read your data even if it wanted to, even if it were hacked, even if a court ordered it to. I wrote a longer breakdown of exactly where these three lines sit in a piece on the concrete differences between encrypted-at-rest, end-to-end, and zero-knowledge, because the distinction is the entire ballgame and most marketing pages blur it on purpose.

The practical test for zero-knowledge is brutally simple: if you forget your password, can the provider help you get your data back? If the answer is yes, they hold something that can decrypt you, and it is not zero-knowledge. If the answer is no, sorry, your data is gone unless you have a recovery mechanism you control, then the design is probably honest. This is the uncomfortable core of real encryption, and it is the single best lie detector you can carry into any privacy sales pitch. A company that promises both perfect zero-knowledge privacy and a friendly 'reset my password and restore my files' button is promising something mathematically incoherent, and one of the two claims is false.

There is a second, subtler layer that almost everyone forgets, and it is where 'really zero-knowledge' starts to wobble even for the good actors. Encryption hides content. It does not automatically hide metadata: the sizes of your files, the number of them, the times you uploaded them, the shape of your folder tree, who you shared a link with. A server can know a tremendous amount about you without ever decrypting a single byte, purely from the pattern of encrypted blobs flowing through it. So when we ask whether Proton Drive is 'really' zero-knowledge, we are actually asking two questions stacked on top of each other: can they read my file contents (the strong claim), and how much can they infer about me even when they cannot (the honest asterisk). Proton does well on the first and, like essentially every syncing cloud service, leaks some of the second.

The two histories: a Swiss privacy company and a solo-built local workspace

Proton started in 2014 as ProtonMail, born out of CERN and a very specific post-Snowden moment when a group of scientists decided that email should be encrypted in a way the provider could not undo. That origin story matters, because it shaped everything Proton built afterward. Proton Mail was designed around OpenPGP from the start, and when Proton expanded into a whole suite, Calendar, VPN, Pass, and eventually Drive in 2022, it carried that same cryptographic DNA forward. Proton Drive is the storage member of a mature, Swiss-based, audited, ISO 27001 and SOC 2 certified company with a real security team, a bug bounty program, and a habit of commissioning independent audits and even funding academic research into its own systems. When Proton says zero-knowledge, there is roughly a decade of institutional practice behind it, and that pedigree is a genuine and honest advantage that a younger project simply cannot fake.

Filarr's history is almost comically different in scale, and I am not going to pretend otherwise. I built it because I wanted one application that held my files, my notes, and a graph linking them together, all encrypted by default, all living on my own disk, with no account required to start. Nothing on the market did exactly that, so I wrote it. Filarr is a desktop app built on Electron and React, it runs on Windows, macOS, and Linux, a mobile version is in progress rather than shipped, and the whole thing is young: it is a 2026-era project, not a 2014-era institution. If you want the fuller version of that origin, I wrote it up in why I built Filarr. I lead with this contrast because it is the honest frame for everything that follows. Proton is a large, battle-tested privacy company that happens to offer storage. Filarr is a focused local-first workspace that happens to be encrypted. Those are different bets, and the differences run all the way down.

The reason these two histories are worth putting side by side is that they explain the philosophical fork we are about to walk into. Proton's answer to 'how do I keep the cloud from reading my data' is to build a better cloud, one that encrypts before upload so thoroughly that the cloud is blind. Filarr's answer is to question the premise: maybe the safest cloud is the one your data mostly never goes to. Neither of those is wrong. They are answers to slightly different fears, and which fear is yours determines which product you should be reading about.

The philosophical fracture: a blind cloud versus no cloud

Here is the fracture, and it is worth slowing down on because it is the thing people actually feel even when they cannot articulate it. Proton Drive is cloud-first done right. Your files live on Proton's servers in Switzerland, encrypted so that Proton cannot read them, and your devices sync down copies as needed. The cloud is the home base; your devices are windows onto it. Filarr is local-first, which means the opposite: your files live on your own disk, encrypted there, and the cloud, if you turn it on at all, is an optional mirror that only ever holds copies. Your device is the home base; the cloud is a convenience. I laid out the full definition and the seven properties that make software genuinely local-first in a separate explainer on local-first software, because the term gets misused almost as badly as zero-knowledge does.

Let me make it concrete with a scenario, because the abstraction hides the stakes. Imagine it is a Tuesday, you are on a train with no signal, and you need a document. On Proton Drive, if that file has been synced to your device or marked available offline, you have it; if it has not, you are looking at a spinner and a loading error until you get bars again, because the source of truth is a server you currently cannot reach. On Filarr, the file is already on your disk in full, because that is the only place it ever primarily lived, so the train, the tunnel, the dead airport wifi, none of it touches you. Now run the scenario forward six months. Proton has an outage, or you stop paying, or Proton as a company has a very bad year. On Filarr, none of that reaches your files, because they were never dependent on a server being alive. On Proton Drive, an outage means a bad afternoon and account termination means you had better have exported everything first. This is not a knock on Proton, whose uptime and longevity are excellent. It is a structural fact: a cloud-first product, no matter how well encrypted, ties your daily access to someone else's infrastructure in a way a local-first product does not.

The flip side of that fracture is just as real, and I will not skip it. A blind cloud is a wonderful thing when your laptop is stolen or your house floods, because your data is safe and complete somewhere else, encrypted, waiting for you to log in from a new machine. Local-first, by default, puts the burden of durability on you: if your disk dies and you never set up a backup or turned on sync, your data dies with it, and no company can bring it back precisely because no company ever had it. So the fracture is not 'one is safe and one is not.' It is 'one defaults to availability through the provider, the other defaults to sovereignty through you,' and each buys its safety by spending a different currency.

What each tool is really for

Proton Drive is, at its core, an encrypted Dropbox. It is built to store and sync files, share them via encrypted links, back up your phone's photos, and give you a private folder in the sky that follows you across devices. It is superb at exactly that. If your mental model is 'I have files, I want them everywhere, and I do not want Google reading them,' Proton Drive is aimed straight at you. It has recently grown document editing with Proton Docs, but the center of gravity is unmistakably file storage and sync, and it is designed to be the calm, encrypted replacement for the mainstream cloud drive you already understand how to use.

Filarr is not trying to be a drive. It is a workspace: notes and files and a graph view that links the two, organized into multi-profile workspaces, with search that reaches inside your documents. The center of gravity is thinking and organizing, not just parking files. It is closer in spirit to an encrypted Notion or a file-aware Obsidian than to a cloud drive, and I have written about that use case directly in pieces on building a genuinely private second brain from notes, files, and a graph and on keeping your whole digital life in one private workspace. The encryption is the floor, not the ceiling: the point of Filarr is what you do on top of it, which is connect ideas to documents and find things fast, all without the underlying data ever sitting in readable form on anyone's server.

So the honest one-line summary of intent is this. Proton Drive answers 'where do my files live safely and sync everywhere.' Filarr answers 'where do my notes, files, and the links between them live, privately, on my own machine.' You can absolutely use both, and plenty of privacy-minded people do: Proton Drive as the encrypted vault for family photos and tax PDFs, Filarr as the local brain for projects and knowledge. Framing them as rivals is a category error. They overlap only at the word 'encrypted,' and that overlap is exactly why the zero-knowledge question is worth untangling rather than hand-waving.

The encryption, in depth, and four threat models

Now the part I actually care about. Let me describe what Proton Drive does cryptographically, as precisely as the public documentation and the independent analysis allow, and then run both products through four concrete threat models so you can see where the guarantees bite. Proton Drive builds on OpenPGP. When you create an account, key pairs are generated on your device. Each file gets a unique AES-256 content key, the file is encrypted in blocks (4 MB blocks, each with its own nonce), and that content key is then wrapped using the key hierarchy tied to the parent folder's share key and ultimately to your account keys. File names and folder structure are encrypted too, not just contents. Your password authenticates via SRP, a protocol that lets the server verify you without ever receiving your actual password, which is a genuinely strong choice. The net effect is that what lands on Proton's servers is opaque ciphertext plus the minimum routing metadata needed to sync it.

Filarr's scheme is built on the same primitives but arranged for a local-first world. Every file is encrypted with AES-256-GCM, an authenticated cipher whose GCM mode gives you both confidentiality and tamper detection in one pass, which I unpacked in detail in what AES-256-GCM actually is and why it matters. Each file has its own File Encryption Key, and those FEKs are wrapped by a Key Encryption Key derived from your password. That two-layer split, per-file keys wrapped by a master key, is the same disciplined pattern that serious systems like Signal and Apple's file protection use, and I wrote up why one global key is dangerous and per-file keys are the correct design in an explainer on KEK and FEK. Key derivation uses PBKDF2-SHA512 at 600,000 iterations, matching the OWASP 2024 guidance, with Argon2id available as an optional stronger derivation. The crucial architectural difference from Proton is where all this happens: in Filarr the encryption runs on your machine against files that already live on your machine, and the cloud is an afterthought, whereas in Proton the encryption runs on your machine specifically so that files can be safely handed to Proton's cloud.

Threat model one: the malicious or compromised server. This is the headline scenario zero-knowledge is meant to defeat. If Proton's servers are breached, the attacker gets encrypted blobs and encrypted metadata, not your readable files, because Proton never held the keys. That is the real win, and it is genuine. For Filarr, the equivalent question only even applies if you turned on optional sync, and even then the backend (Cloudflare R2, or your own S3-compatible bucket if you use bring-your-own-storage) stores only opaque encrypted blobs, so a breach of that backend yields noise, exactly as I described in how Filarr's optional cloud sync stays zero-knowledge. On this threat model both products pass, and this is the model where 'zero-knowledge' most clearly earns the name. The difference is that Filarr's attack surface here is opt-in and can be zero if you never sync at all, while Proton's is always present because the cloud is the product.

Threat model two: the stolen or seized laptop. Your device is gone, physically, in someone else's hands. Here the picture inverts. Proton Drive on a logged-in device typically has cached, decrypted or decryptable content available for the convenience of the logged-in session, so a thief with an unlocked machine may reach your synced files just as they would with any cloud client; your protection leans heavily on your device's own lock screen and full-disk encryption. Filarr keeps files encrypted at rest on your disk by design, wrapped under your password-derived key, so a powered-off or locked Filarr vault is ciphertext even to someone holding the drive. This is the threat model where local-first encryption at rest quietly shines and where a cloud client's convenience caching can work against you. Neither is magic: if your machine is unlocked and the app is open, both are exposed, which is why device-level security still matters underneath everything.

Threat model three: the weak password. This is the one nobody wants to hear about. Zero-knowledge means the provider cannot help you, but it also means your password is very nearly the whole wall. If you choose 'summer2024,' no cipher on earth saves you, because an attacker who gets the ciphertext can grind guesses against the key derivation offline. Both Proton and Filarr mitigate this with slow, salted key derivation that makes each guess expensive, and Filarr's optional Argon2id specifically raises the cost of large-scale guessing with memory-hard work. But the honest truth for both products, and for every real zero-knowledge system, is that a weak password is the soft underbelly, and the encryption is only ever as strong as the secret feeding it. This is not a flaw in either design; it is the unavoidable tax of a system where no one can bail you out.

Threat model four: the legal request. A government or litigant serves the provider with a valid order to hand over your data. This is where zero-knowledge stops being a nerdy detail and becomes the entire point. Proton, subject to Swiss law, can be compelled to hand over what it has, but what it has for Drive is encrypted blobs and metadata, not readable contents, so it cannot produce your plaintext because it does not possess the means to decrypt it. It can, and does when legally forced, produce metadata. Filarr, in the local-only mode most people run, presents no provider to subpoena at all, because there is no company holding your data; a request would have to come to you and your device directly. On this model both offer real protection for content, and the local-first design offers the additional property that there may be no third party in the loop to compel in the first place. If your specific worry is 'who can be forced to give up my files,' this is the model to weigh most heavily.

Where 'zero-knowledge' gets an asterisk

So is Proton Drive really zero-knowledge? For file contents, file names, and folder structure, yes, and that is not a small thing. But intellectual honesty requires three asterisks. First, metadata: Proton, like any syncing service, sees file sizes, upload timestamps, the number of objects, and sharing activity, and that pattern data can be revealing even without decryption. Second, the browser problem: when you use Proton Drive in a web browser, the encryption runs in JavaScript that Proton's own servers deliver to you fresh each session, which means you are trusting Proton not to serve you a subtly malicious script, a trust you do not have to extend to a native app you installed once and can inspect. This is a well-known structural weakness of all browser-based end-to-end encryption, not a Proton-specific failing, but it is real, and it is why the native apps are cryptographically preferable to the web app. Third, and to Proton's enormous credit that we even know this, an ETH Zurich master's thesis by Léa Micheloud, supervised by the cryptographer Kenny Paterson, analyzed Proton Drive's OpenPGP design and found weaknesses, notably that failed signature checks did not always carry consequences, which could enable integrity or authenticity attacks by a malicious server. Proton engaged with that research rather than hiding from it, which is exactly what a trustworthy company does, and the confidentiality guarantee (the server cannot read your files) was not what was broken.

I raise these not to knock Proton off a pedestal but because 'really zero-knowledge?' deserves a real answer, and the real answer is 'yes on confidentiality, with honest limits on metadata, a browser-trust caveat, and a history of taking its own audit findings seriously.' That is a far better report card than almost any mainstream cloud can produce. It also, incidentally, illustrates why the local-first camp is nervous about the whole cloud-first model even when it is done well: the metadata leakage and the server-trust surface are inherent to putting your data on someone else's machine at all, however blind that machine is. Filarr is not immune to key-derivation weakness or a bad password, but it sidesteps the metadata and server-trust surfaces entirely in local-only mode, simply by not sending your data anywhere. That is the structural argument, and it is worth understanding on its own terms, which I made at length in how local encryption and classic cloud diverge the moment data leaks.

Sync architecture and multi-device reality

How syncing actually works determines a lot of your day-to-day experience, so let me be concrete. Proton Drive's model is the classic cloud hub: your files live on Proton's servers as encrypted blobs, and each device (desktop app, mobile app, web) pulls down and pushes up changes against that authoritative copy. Multi-device is effortless because the server is the single source of truth: log in on a new phone, and your whole encrypted drive is available to sync, no file shuffling required. Offline access works for whatever has been cached or marked for offline use, and when the server is unreachable you operate on that cached subset until connectivity returns. If Proton has an outage, syncing pauses and you keep working on local copies; when it comes back, changes reconcile. If you stop paying, your account moves to a restricted state and you retain access to get your data out, but you are on a clock and above the free limit you cannot add new files.

Filarr's model starts from the other end. The authoritative copy is on your disk, always, in full. If you never enable sync, there is no server in the picture at all: multi-device simply is not a feature you have turned on, and your data has a home of exactly one. If you do enable the optional sync, Filarr encrypts locally and pushes opaque blobs to Cloudflare R2 or your own bucket, and other devices pull them down and decrypt locally. The philosophical consequence is that a server outage is a non-event for your access, because you were never reading from the server to begin with; sync just catches up later. Account termination or a lapsed subscription cannot lock you out of your own files, because the files are yours on your disk and the subscription only ever bought you the mirror. The trade is honest and it cuts both ways: Filarr's multi-device story is younger and less turnkey than Proton's polished cross-platform sync, and with mobile still in progress, the seamless phone-and-laptop experience that Proton nails today is exactly where Filarr is still maturing.

The practical upshot for a multi-device household is that Proton Drive will feel more finished right now, full stop. It has native clients across Windows, macOS, Linux, Android, and iOS plus a capable web app, and the sync just works with the fit and finish of a company that has been shipping this for years. Filarr will feel more sovereign but less ubiquitous: rock-solid on the desktop you installed it on, with sync as a deliberate choice rather than an assumed backbone, and mobile arriving rather than arrived. If your life genuinely spans four devices and you need any file on any of them at any moment with zero friction, be honest with yourself that this is Proton's home turf today.

Recovery and losing access

This is the section that separates real encryption from theater, so let me be blunt. In a true zero-knowledge system, forgetting your password should be catastrophic unless you set up a recovery mechanism that you control, because if the provider could reset your way back in, they would by definition hold a key and the whole edifice would be a lie. Proton handles this with recovery methods you opt into: a recovery phrase and recovery file that you save, plus account recovery options. The critical nuance, and Proton is fairly upfront about it, is that resetting your login password is not the same as recovering your data encryption keys; without your recovery phrase or file, resetting access can leave previously encrypted data unreadable, precisely because the data keys were protected by the credential you lost. That is not Proton being cruel; that is Proton being honest about what zero-knowledge costs. Any service that promises effortless full recovery of encrypted data after a forgotten password is quietly telling you it can read your data.

Filarr's recovery is a 24-word BIP-39 phrase, the same standard used by cryptocurrency wallets, generated when you set up your vault. That phrase is the lifeboat: if you forget your password, the phrase can restore access to your keys, and if you lose both the password and the phrase, your data is unrecoverable by anyone, including me, because there is no server-side copy of your keys and no backdoor to insert one. I want to sit on that sentence for a moment, because it is the whole ethos: the same property that makes Filarr genuinely private also makes it genuinely unforgiving. Write down your recovery phrase, store it somewhere physical and safe, and treat it like the master key to your house, because that is exactly what it is. I wrote a full guide to doing backups without undermining the encryption in how to back up encrypted notes without breaking zero-knowledge, and the principles apply just as well to Proton's recovery file as to Filarr's phrase.

The death-of-the-account scenario is worth a sentence too, because people plan estates and forget their data. With Proton, a heir would need your credentials and recovery materials; Proton cannot simply hand your files over, again because it cannot read them. With Filarr, your files sit on your disk in your possession, so inheritance is a matter of someone gaining access to your device and your recovery phrase, which you can arrange deliberately through whatever secure means you use for other secrets. In both cases the lesson is identical and unavoidable: in a real zero-knowledge world, recovery is a responsibility that moves from the provider to you, and the price of nobody being able to read your data is that nobody can rescue it for you either.

The comparison, at a glance

The table below compresses the whole comparison, but read it with the prose in mind, because a checklist flattens exactly the nuances that matter. A row that says both products encrypt at AES-256 hides the fact that they are protecting different things in different places for different reasons, and a row about mobile that favors Proton today may read differently in a year as Filarr's mobile ships. Treat this as a map, not the territory.

	Proton Drive	Filarr
Core purpose	Encrypted cloud storage and file sync	Local-first encrypted workspace (notes, files, graph)
Primary data location	Proton's servers (Switzerland), synced to devices	Your own disk; cloud is optional mirror
Encryption	OpenPGP, per-file AES-256 content keys, encrypted names and folders	AES-256-GCM per file, per-file FEK wrapped by password-derived KEK
Key derivation	Password-derived key hierarchy, SRP authentication	PBKDF2-SHA512 600k iterations, optional Argon2id
Zero-knowledge on contents	Yes, by default, all tiers	Yes, and no server involved at all in local-only mode
Metadata exposure	Sizes, timestamps, structure visible to server	None in local-only mode; opaque blobs if sync enabled
Offline access	Cached or marked-offline files only	Everything, always, by design
Recovery	Recovery phrase and file (opt-in)	24-word BIP-39 phrase
Platforms	Windows, macOS, Linux, Android, iOS, web	Windows, macOS, Linux; mobile in progress
Independent audits	Yes (Securitum 2024 web client, ETH academic analysis)	Younger project, open source client (BSL 1.1)
Pricing	Free 5GB; Drive Plus about 3.99/mo; Unlimited 9.99/mo	Free forever local; sync from 4/mo
Open source	Web client open source, audited	Desktop client open source under BSL 1.1

Where Proton Drive genuinely wins

Let me be unambiguous, because a comparison where the author's product sweeps every category is a comparison you should not trust. Proton Drive wins on maturity, and it is not close. This is a decade-old company with certifications, audits, a bug bounty, and academic scrutiny it invited onto itself. When you hand files to Proton, you are trusting infrastructure that has been probed, attacked, and hardened for years, run by an organization whose entire business identity is privacy. Filarr is a young project, and no amount of clean cryptography substitutes for the institutional track record that Proton has earned the slow way. If your threat model includes 'I need to trust that the people who built this have survived real adversarial pressure,' Proton has a story Filarr cannot yet tell.

Proton Drive also wins decisively on cross-platform reach and sync polish. Native apps on five platforms plus a genuinely usable web client, seamless multi-device sync, phone photo backup, and encrypted sharing that your non-technical relatives can actually use: this is a finished, consumer-grade product. If you want any file on any device instantly, if you want to back up your phone's camera roll automatically, if you want to send a grandparent an encrypted link they can open without installing anything, Proton does all of that today, smoothly. Filarr's mobile is still in progress and its sync is a deliberate opt-in rather than an assumed backbone, so for the pure 'my files, everywhere, effortlessly' use case, Proton is simply the more complete tool right now.

And Proton wins on the suite effect. Proton Drive is one member of an ecosystem that includes encrypted Mail, Calendar, VPN, Pass, and Docs, often bundled at a single price. If you want your email, your passwords, your VPN, and your files all under one privacy-respecting Swiss roof with one login and one subscription, that integrated bundle is a real, tangible value that a single-purpose workspace cannot match. For a lot of people, 'move my whole digital life away from Google in one coherent step' is best answered by Proton, and I would not argue otherwise. Filarr does one category of thing; Proton does many, competently, together.

Where Filarr genuinely wins

Filarr wins on sovereignty, and it is the cleanest win in the whole comparison. Your data lives on your disk, encrypted, and it does not require any server to be alive, any subscription to be current, or any company to remain in business for you to open your files tomorrow morning. Proton is a blind cloud, which is excellent, but it is still a cloud, and your daily access is still mediated by their infrastructure and your account standing. Filarr's default is that nothing mediates your access to your own files except your own password. If the deepest version of your worry is not 'can the cloud read my data' but 'why is my data on someone else's computer at all,' Filarr answers the question Proton cannot, by removing the premise.

Filarr wins on the offline and metadata story that falls straight out of that architecture. Everything is available offline always, because local is the only place it fundamentally lives, so trains, tunnels, flights, and dead wifi are simply not your problem. And in local-only mode there is no server accumulating your file sizes, timestamps, and folder shapes, so the metadata leakage that even a perfect zero-knowledge cloud cannot avoid does not exist, because there is no server to leak to. Proton is honest and good about minimizing what it sees, but it cannot get to zero on metadata while being a syncing cloud, and Filarr can, simply by not being one unless you ask it to be.

Filarr wins on being a workspace rather than a drive. This is less a privacy point than a 'what is the product for' point, but it matters. Filarr links notes to files in a graph, searches inside your documents, and organizes everything into multi-profile workspaces, so it is a place to think and connect, not just a place to park bytes. If what you actually want is an encrypted brain, notes and PDFs and the web of links between them, all private by default, that is Filarr's core competency and it is squarely outside Proton Drive's mission. I compared these two products more narrowly, feature by feature, in a dedicated Proton Drive versus Filarr breakdown if you want the head-to-head without the zero-knowledge framing wrapped around it.

Migrating, in either direction

Moving from Proton Drive into Filarr, or the reverse, is mercifully undramatic, because at the end of the day both deal in ordinary files. To leave Proton Drive, you download your files through the app or web client, which decrypts them locally into normal files on your disk, and then you import that folder into a Filarr workspace, where Filarr re-encrypts each file under your own per-file keys as it ingests them. The friction is not technical so much as logistical: a large drive means a large download, and you will want to verify the copy landed intact before you delete anything on either side. What you gain in the move is local sovereignty and the notes-plus-graph layer; what you give up, if you were relying on it, is Proton's effortless multi-device sync and phone backup, so go in clear-eyed about the trade.

Going the other direction, from Filarr to Proton Drive, is equally straightforward: Filarr can export your files back into plain form on your disk, and you upload that folder to Proton Drive, which encrypts it into their scheme on the way up. The thing to understand in both directions is that there is a brief window where your data exists as decrypted files on your local disk between the two encrypted worlds, so do the migration on a trusted machine, ideally one with full-disk encryption, and clean up any intermediate plaintext copies when you are done. This is not a Filarr-specific or Proton-specific caution; it is true of moving between any two encrypted systems, because the only common format they both speak is the plaintext in the middle.

The honest meta-point about migration is that the ease of leaving is itself a privacy feature, and both products pass this test. Neither one locks your data in a proprietary format you cannot get out of; both let you walk away with your files as normal files. That is exactly how it should be, and it is worth rewarding with your trust, because a service confident enough to make leaving easy is usually a service that is not quietly depending on lock-in. If you are coming from a mainstream cloud instead and want a fuller walkthrough of doing this without losing anything, the mechanics generalize from my guide on moving a Notion workspace into an encrypted app.

Pricing, decoded, with real scenarios

Numbers first, honestly. Proton Drive is free for 5GB (you start at 2GB and unlock the rest by completing a few onboarding steps within your first month), with paid tiers rising from around 3.99 per month for Drive Plus at 200GB on annual billing, up to Proton Unlimited at about 9.99 per month, which bundles 500GB of storage together with Mail, VPN, Pass, and more. Filarr is free forever for local use, with no storage cap imposed by me because the storage is your own disk, and optional cloud sync starts at 4 per month. Those two pricing shapes are not really comparable line for line, because you are buying different things: with Proton you are largely buying storage space and a suite, and with Filarr you are buying an optional sync mirror on top of software that is fully functional and free without it.

Scenario one: the privacy-minded individual with a laptop and a phone, maybe 50GB of documents and photos, who wants them encrypted and synced everywhere. Proton Drive Free might just fit if you are frugal, but realistically you land on Drive Plus at roughly 3.99 per month for the headroom and the smooth multi-device sync, and that is genuinely good value for a polished encrypted cloud. On Filarr, the local workspace is free, and if you want cross-device sync you add it from 4 per month, but with mobile still in progress the phone half of that story is not fully there yet, so for this exact 'everywhere, now' profile Proton is both the more finished and the more sensible spend today.

Scenario two: the person who wants an encrypted second brain, lots of notes and project files linked together, living entirely on one main computer, with strong privacy and no interest in paying a monthly cloud bill. Filarr is free, full stop, and it does the notes-files-graph job that Proton Drive does not do at all, so your monthly cost is zero and you own everything locally. Proton Drive is the wrong tool for this profile regardless of price, because it is storage, not a workspace, so the comparison is less about euros and more about fit. If this is you, the cheapest correct answer and the best-fitting answer are the same answer, and it is not the cloud drive.

Scenario three: the household that wants to leave Google entirely, email and all, across several people and devices, with a real support burden if things go wrong. Proton Unlimited or a Family plan at the 9.99-and-up range is the coherent move, because you are buying a whole integrated, mature, supported ecosystem, and the per-euro value of collapsing Mail, VPN, Pass, and Drive into one trustworthy Swiss bundle is high. Filarr does not compete for this job and should not pretend to; it is one specialized instrument, not an orchestra. The pricing lesson across all three scenarios is the same: match the spend to the actual job, and do not let a low headline number tempt you into the wrong category of tool.

Open source and licensing, and what it means for you

Open source matters for encrypted software in a way it does not for most apps, because 'the server cannot read my data' is a claim you would ideally verify rather than trust. Proton has made real moves here: its web client is open source and was independently audited by Securitum in 2024, and Proton has actively supported academic scrutiny of its cryptography, including the ETH Zurich thesis I mentioned. That combination, published code plus commissioned audits plus welcomed outside research, is close to the gold standard for a company asking you to believe its zero-knowledge claims, and it is a big part of why the answer to 'is Proton really zero-knowledge' is 'yes, and you do not have to take their word for it.'

Filarr's desktop client is open source too, published on GitHub under the Business Source License 1.1, which I chose deliberately and wrote about in why Filarr went open source under BSL 1.1. BSL 1.1 is worth understanding precisely: it makes the source fully readable and inspectable, which is the property that matters for verifying encryption claims, while restricting certain commercial uses for a period before the code converts to a fully open license. For you as a user, the practical meaning is that you or anyone can read exactly how Filarr encrypts your files and confirm that the keys never leave your control, which is the whole point of publishing crypto code. One clarification I always insist on, because people conflate them: the Filarr desktop client is BSL 1.1, but the Filarr website is a separate repository under AGPL-3.0, and it is worth keeping the licence of the app you trust with your data distinct from the licence of the marketing site.

The honest comparison on this axis is that Proton's transparency is more established and more externally validated today, while Filarr's is younger but real and improving. Both publish code, which already puts them in a small and respectable minority; the mainstream clouds publish nothing and simply ask for faith. If you are the kind of person for whom 'show me the code or I do not believe the privacy claim' is non-negotiable, both of these products can look you in the eye, and that shared willingness to be inspected is, honestly, the strongest signal either of us can give you that our zero-knowledge claims are not marketing.

Which one is for you

If you are a privacy-conscious individual who mainly wants files encrypted and synced across a laptop and a phone, and you want it to just work today, choose Proton Drive. Your central need is availability everywhere with the server unable to read you, and Proton nails exactly that, on every platform, with the maturity and support to back it up. Filarr would ask you to wait on mobile and to think about sync as an add-on, which is the wrong set of trade-offs for your specific profile. Do not overthink it: Proton is aimed at you.

If you are a knowledge worker, developer, or writer who wants an encrypted second brain, notes and files and the links between them, living on your own machine and answerable to no server, choose Filarr. Your central need is a private workspace you own outright, not a drive, and Filarr's local-first architecture, per-file encryption, and graph-linked notes are built for precisely that. Proton Drive is a fine cloud but it is not a workspace, and forcing it into that role would leave you assembling something clumsy out of storage and Docs when a purpose-built tool exists. This is your fit.

If you are a self-hoster or a maximalist who does not want your data on anyone's server at all, choose Filarr in local-only mode, or Filarr with bring-your-own-storage pointed at a bucket you control. Your central need is that the premise of the blind cloud still bothers you, and only removing the cloud from the critical path answers it. Proton, however blind, is still a cloud you do not run, so for the true sovereignty maximalist it is one trust relationship too many, and Filarr's ability to simply not phone home is the feature you came for.

And if you are trying to move your entire family off Google, email, passwords, VPN, and files together, in one coherent, supported, mature step, choose Proton, on Unlimited or a Family plan. Your central need is an integrated ecosystem with institutional trust and real support, and that is Proton's greatest strength and the one thing a single-purpose workspace like Filarr explicitly does not offer. Use Filarr later, if you want, for the thinking-and-organizing layer on top; but the big migration is Proton's job.

Conclusion

So, is Proton Drive really zero-knowledge? Yes, in the way that counts most: the server genuinely cannot read your file contents, your file names, or your folder structure, on every tier, verified by open-source code and independent audits, backed by a decade-old privacy company that funds research into its own weaknesses rather than hiding them. That is a rare and real thing, and if you have been carrying a vague suspicion that it was too good to be true, you can mostly set that suspicion down. The asterisks, metadata visibility, the browser-JavaScript trust surface, and the ordinary reality that a weak password undoes any cipher, are honest limits, not disqualifications, and they apply in some form to every product in this space including mine.

The deeper thing I hope you take away is that 'zero-knowledge' is the right question but not the last question. Proton Drive answers it by building a cloud so blind it cannot betray you. Filarr answers the worry underneath it by mostly not sending your data to a cloud at all. Those are different philosophies serving different fears, and the mature move is to know which fear is actually yours before you pick. If you want your files safe and synced everywhere by a company you can trust, Proton Drive is one of the best answers on the market and I will happily say so. If you want your notes, files, and ideas encrypted and living on your own disk, sovereign and offline by default, that is what I built Filarr to be. Pick the one that matches the sentence you would actually say out loud about your data, and you will have picked correctly.

FAQ

Is Proton Drive really zero-knowledge, or is that marketing? It is genuinely zero-knowledge on file contents, file names, and folder structure, by default and on all tiers, which is verifiable through Proton's open-source web client and independent audits. The honest caveats are that Proton still sees metadata like file sizes and timestamps, the browser version relies on JavaScript Proton serves you each session, and no encryption survives a weak password. On the core claim, that the server cannot read your files, it holds up.

Can Proton Drive recover my files if I forget my password? Not fully, and that is actually the proof it is real zero-knowledge. Resetting your login password is not the same as recovering your data encryption keys; without your recovery phrase or recovery file, previously encrypted data can become unreadable. Any service promising effortless full recovery after a forgotten password is quietly admitting it can read your data.

How is Filarr different from Proton Drive if both are encrypted? Proton Drive is an encrypted cloud drive: your files live on Proton's servers, encrypted so they cannot read them, and sync to your devices. Filarr is a local-first encrypted workspace: your notes and files live on your own disk, encrypted there, with cloud sync as an optional mirror. Proton is storage and sync; Filarr is a place to think, organize, and link notes to files, that happens to be encrypted by default.

Does Filarr's optional sync stay zero-knowledge? Yes. Files are encrypted on your device before upload with per-file AES-256-GCM keys, and the backend (Cloudflare R2, or your own S3-compatible bucket) stores only opaque encrypted blobs. Your key never reaches the server in cleartext, so a breach of the sync backend yields unreadable noise. In local-only mode there is no server involved at all.

What encryption does each one use? Proton Drive builds on OpenPGP with per-file AES-256 content keys, encrypting file contents plus names and folder structure, and authenticates your password via SRP. Filarr uses AES-256-GCM per file, with each file's key wrapped by a Key Encryption Key derived from your password using PBKDF2-SHA512 at 600,000 iterations, with optional Argon2id. Both are sound modern designs; the main difference is where the encryption happens and where your data primarily lives.

Which is better for using my files offline? Filarr, by design. Everything is on your disk in full, so offline access is total and permanent regardless of any server. Proton Drive gives you offline access only to files that are cached or explicitly marked for offline use, because its source of truth is the cloud, so a tunnel or an outage limits you to whatever your device happens to be holding.

Is Proton Drive's web app as secure as the native apps? Slightly less so in principle, for a structural reason shared by all browser-based end-to-end encryption: the web app runs cryptography in JavaScript that Proton's servers deliver each session, so you are trusting Proton not to serve a malicious script. The native desktop and mobile apps, which you install once, do not carry that per-session trust in the same way. For maximum assurance, prefer Proton's native clients over the browser.

Should I use both Proton Drive and Filarr? Plenty of privacy-minded people do, and it can be a sensible split. Use Proton Drive as the mature, cross-device encrypted vault for things like family photos and tax documents that you want synced everywhere and backed up off your machine. Use Filarr as the local, sovereign workspace for your notes, projects, and the graph of links between your files and ideas. They overlap only at the word encrypted, so they complement each other more than they compete.