Yes — Internxt is zero-knowledge. Files are encrypted on your device with AES-256 before they reach Internxt's servers, so Internxt only ever holds ciphertext and cannot read them. It is based in Valencia, Spain, stores files across European data centres under GDPR, publishes its client applications as open source, and has had those applications and its cloud services penetration-tested by Securitum, a European security firm. If you came here to find out whether the claim survives inspection, it does. What follows is how to check it yourself, what zero-knowledge does not cover, and the narrow axes on which Internxt and other zero-knowledge providers actually differ once they have all cleared that bar.
What "zero-knowledge" means, and what Internxt does
Zero-knowledge storage means the provider has no knowledge of your file contents. Encryption happens on your device, the key never reaches the provider in a form it can use, and what arrives at the server is ciphertext the provider cannot decrypt. "End-to-end encrypted" describes the same property from the other direction.
The consequence is the part that matters: there is no plaintext on the server to read, hand over, scan, or train a model on. That is a stronger guarantee than a privacy policy, because it is a property of the architecture rather than a promise about behavior. A policy can be rewritten; a server that only ever receives ciphertext cannot quietly begin reading files.
Internxt implements this with AES-256 applied client-side, and the scope extends past the file bytes: filenames and folder structure are encrypted too, so the directory tree is not a plaintext index sitting beside the encrypted contents. That scope is worth checking explicitly for any provider, because "encrypted files" and "encrypted files, names and structure" are different products.
How to verify the claim yourself
You do not have to take a zero-knowledge label on faith, and Internxt is one of the providers where you genuinely do not have to. Three things back the claim.
- Open-source clients. Internxt publishes the source for its desktop, web, mobile and CLI applications: the web and mobile apps under AGPL-3.0, the desktop app, SDK and CLI under MIT. The encryption happens in code you can read, so the claim is inspectable rather than asserted. This is the check that matters most: the client is where the key is derived and where plaintext either does or does not leave your machine.
- An independent penetration test. Internxt has had its web, mobile and desktop applications and its cloud services penetration-tested by Securitum, a European security firm. That is a third party looking for the gap between the architecture as described and the system as built.
- An ISO/IEC 27001:2022 certification. Independently verified, covering the organization's information-security management rather than the cryptography specifically — a different kind of assurance from the pen test, and worth counting separately rather than collapsing the two into "audited".
Read together, those are stronger evidence than most storage products offer. On the question this page exists to answer, there is no hedge to add: Internxt is zero-knowledge, and the claim is checkable.
What zero-knowledge does not cover
Zero-knowledge is necessary, not sufficient, and a fair answer has to name what it leaves open — for Internxt and for other providers making that claim.
- A compromised device. If your own machine is infected, an attacker reads plaintext before encryption happens. No server-side property fixes that.
- Account compromise. Someone with your password and second factor is you, as far as the system is concerned. Zero-knowledge protects you against the provider, not against a stolen credential.
- Some metadata. Contents, filenames and folder structure being encrypted still leaves observable facts — file sizes, timestamps, upload patterns. How much of that is protected varies by product and is worth checking rather than assuming.
- The quantum horizon. Classical zero-knowledge encryption is not automatically post-quantum. Under "harvest now, decrypt later" — an adversary copying ciphertext today to decrypt once a quantum computer exists — the relevant question is not whether the file is encrypted now but whether the key exchange that protects it survives. Zero-knowledge alone does not answer that.
Compare the authentication trust model as well as the encryption format; a cipher choice alone does not establish zero-knowledge architecture.
Where Internxt and ShieldFive actually differ
ShieldFive encrypts files on the device, and the password never reaches its servers: the browser sends only an Argon2id-derived login value, and the vault key is derived separately on the device. The web app’s code is served by ShieldFive, so the client delivered on each visit stays part of the trust boundary. This is not an absolute guarantee that the provider cannot decrypt files.
Internxt's post-quantum layer is a hybrid of Kyber-512 — security category 1, the lowest of the three standardized levels, from a pre-standard round-3 library — and elliptic-curve keys. It wraps account and sharing keys, not the per-file content keys. Internxt's newer Mail product uses ML-KEM-768. ShieldFive web uploads default to ML-KEM-1024/XChaCha20-Poly1305 with AES-GCM fallback. Android also defaults to the hybrid format, with the same AES-GCM fallback, and reads both formats; post-quantum protection does not apply to every upload.
| Capability | Internxt | ShieldFive |
|---|---|---|
| Zero-knowledge | Yes — every file, client-side | Client-side encryption with authentication-service trust |
| File-content cipher | AES-256 | Web and Android: XChaCha20-Poly1305 or AES-GCM |
| Post-quantum strength | Hybrid Kyber-512 (NIST level 1, pre-standard) | ML-KEM-1024 (NIST level 5, FIPS 203), hybrid |
| Post-quantum scope | Account and sharing keys, not per-file content keys | Hybrid default on web and Android, AES-GCM fallback |
| EU data residency | Yes (Spain / EU data centres) | Yes |
| Open source | Clients — web, mobile (AGPL-3.0); desktop, SDK, CLI (MIT) | Crypto core (Apache-2.0), public spec + vectors |
| External assessment | Securitum penetration test, ISO/IEC 27001:2022 | None completed — published internal review |
| Free tier | 1 GB | 10 GB, no card |
One row in that table points away from ShieldFive — external assessment — and it is not a footnote.
Where Internxt is ahead
A completed independent assessment. Internxt has been penetration-tested by Securitum and holds an independently verified ISO/IEC 27001:2022 certification. ShieldFive has neither. Its crypto core is open, with a public specification and test vectors, and it has published an internal security review — but an internal review is not an external audit and should not be counted as one. If a completed third-party assessment is a hard requirement, Internxt is ahead of ShieldFive today, and no amount of parameter-set comparison changes that.
Copyleft licensing. Internxt's web and mobile clients are AGPL-3.0, which obliges downstream modifications to stay open; its desktop app, SDK and CLI are MIT. ShieldFive's crypto core is Apache-2.0, which is more permissive. Neither is better in the abstract; if copyleft is what you want, Internxt's choice fits it.
Track record. Internxt has shipped this architecture for longer than ShieldFive has existed. Maturity is a real property and Internxt has more of it.
If you are comparing, not just checking
Many people search this question mid-comparison — confirming Internxt is legitimate before weighing it against something else. It is legitimate. If the next question is how it stacks up, the Internxt alternative comparison puts the two products side by side in more detail, ten zero-knowledge providers rated honestly places Internxt in the wider field, and post-quantum encrypted cloud storage explains why the ML-KEM parameter set matters for files with a long confidentiality lifetime and why it matters very little for files without one. If the term itself is what you are pinning down, what zero-knowledge cloud storage means is the definition page.
For a large class of buyers, an EU-hosted, open-source, independently tested, zero-knowledge product with hybrid Kyber-512 on its account and sharing keys is the right answer, and Internxt is that product.
Frequently asked questions
Can Internxt read the files I upload?
No. Files are encrypted on your device with AES-256 before upload, so Internxt receives ciphertext and holds no key that decrypts it. This is a property of how the system is built, not a policy commitment — there is no plaintext on the server to read.
Has Internxt's zero-knowledge claim been independently tested?
Yes. Internxt's web, mobile and desktop applications and its cloud services have been penetration-tested by Securitum, a European security firm, and Internxt holds an independently verified ISO/IEC 27001:2022 certification. Combined with open-source clients, that is a stronger evidence base than most storage products publish.
Does Internxt encrypt filenames and folder structure too?
Yes. Internxt applies zero-knowledge encryption to every file along with the filename and folder structure, so the directory tree is not left as a plaintext index next to encrypted contents. Some observable metadata — file sizes, timestamps — remains outside what any provider's content encryption covers.
Is Internxt zero-knowledge on the free plan?
Yes. Internxt's zero-knowledge encryption applies on the free tier, which its pricing page lists at 1 GB. It is not an add-on or a paid folder, which is the pattern some other providers use. Free-tier sizes change, so verify current terms before relying on the number.
Is Internxt's Kyber-512 enough for long-lived confidential files?
Internxt's hybrid Kyber-512 sits at NIST security category 1 and wraps account and sharing keys, not the per-file content keys. Cipher parameters are only one part of a storage security assessment. ShieldFive web uploads default to ML-KEM-1024/XChaCha20-Poly1305 with AES-GCM fallback. Android also defaults to the hybrid format, with the same AES-GCM fallback, and reads both formats; post-quantum protection does not apply to every upload. Review the authentication trust model, recovery process and audit evidence as well.
How does ShieldFive’s trust model differ from Internxt’s?
ShieldFive encrypts files on the device, and the password never reaches its servers: the browser sends only an Argon2id-derived login value, and the vault key is derived separately on the device. The web app’s code is served by ShieldFive, so the client delivered on each visit stays part of the trust boundary. This is not an absolute guarantee that the provider cannot decrypt files. ShieldFive web uploads default to ML-KEM-1024/XChaCha20-Poly1305 with AES-GCM fallback. Android also defaults to the hybrid format, with the same AES-GCM fallback, and reads both formats; post-quantum protection does not apply to every upload. ShieldFive stores encrypted file data in the EU, publishes its crypto core under Apache-2.0, and has no completed external security audit. Its applications are not fully open source.
Internxt's details on this page restate the fact-checked comparison in the Internxt alternative article, which reflects Internxt's public documentation as of 22 September 2026. Both will be updated as the products change.