When you store files in Google Drive, Dropbox, or iCloud, the provider holds the encryption keys. That means they can decrypt your files — to power search features, train AI models, or comply with law-enforcement requests. For everyday photos and grocery lists that's probably fine. For passports, medical records, tax returns, and signed contracts, it's a meaningful privacy risk.
This guide covers the best zero-knowledge encrypted document storage apps in 2026 — services where only you hold the key, and the provider genuinely cannot read your files even if it wanted to. If you're new to the concept, our explainer on how zero-knowledge encryption works breaks down exactly why that matters.
What to look for in encrypted document storage
- Zero-knowledge architecture — encryption happens on your device before upload. The provider never sees your key.
- Strong encryption standard — AES-256 (preferably in GCM mode, which also detects tampering) is the current benchmark.
- Secure key storage — your key should live in your device's hardware security module: iOS Keychain, Android Keystore, or Windows DPAPI — not just software memory.
- Recovery option — a well-designed recovery password lets you restore access on a new device without giving the provider your key.
- Document-specific features — storage alone may not be enough. Signing, scanning, and AI analysis built on top of encrypted storage gives you a complete secure document workflow.
1. PrimeDocu — Best for sensitive document storage with built-in tools (free 1 GB)
PrimeDocu is built specifically for sensitive documents. Every file is encrypted on-device using AES-256-GCM before upload, with the key stored in iOS Keychain, Android Keystore, or Windows DPAPI. The result is true zero-knowledge storage — PrimeDocu staff cannot read your documents even if compelled.
What makes PrimeDocu stand out from generic encrypted storage services is the document-specific feature set: you can sign PDFs, scan paper documents with your phone camera, get AI-powered summaries, and extract key dates for smart reminders — all with encryption built in at the core.
- Encryption: AES-256-GCM, on-device before upload
- Key storage: iOS Keychain / Android Keystore / Windows DPAPI (hardware-backed)
- Free tier: 1 GB encrypted storage, unlimited PDF signing — free forever
- Paid plans: Pro ($9.99/month, 5 GB), Premium ($19/month, 25 GB)
- Recovery: Optional recovery password (strongly recommended)
- Compliance: GDPR and CCPA compliant
Best for: contracts, passports, medical records, NDAs, tax returns, and any document you sign or scan on a regular basis.
2. Tresorit — Best for business teams requiring zero-knowledge compliance
Tresorit is a well-established zero-knowledge cloud storage service based in Switzerland. It uses AES-256 encryption with keys held client-side and has strong compliance credentials for GDPR, HIPAA, and ISO 27001. The product is polished and the service has an excellent track record.
- Encryption: AES-256, client-side (zero-knowledge)
- Free tier: None — 14-day free trial only
- Paid plans: From $12/user/month (annual billing)
- Best for: law firms, healthcare providers, finance teams with compliance requirements
Limitation: no free tier makes it inaccessible for personal use; higher price point than most alternatives.
3. ProtonDrive — Best for users in the Proton ecosystem (free 1 GB)
Proton — the company behind ProtonMail — launched ProtonDrive as a zero-knowledge cloud storage product. Files are end-to-end encrypted before upload using PGP-based encryption, and the 1 GB free tier is generous for a privacy-first service.
- Encryption: End-to-end (OpenPGP + AES-256)
- Free tier: 1 GB (shared across Proton services)
- Paid plans: From $3.99/month (Proton Unlimited includes 500 GB)
- Best for: users who already use ProtonMail and want a unified privacy-first suite
Limitation: pure storage — no document signing, scanning, or AI features; 1 GB is shared with ProtonMail.
4. Internxt — Best open-source zero-knowledge option (free 1 GB)
Internxt is an open-source, decentralised cloud storage provider with zero-knowledge encryption. Files are encrypted client-side using AES-256 and the code is publicly auditable on GitHub. The free 1 GB tier requires no credit card.
- Encryption: AES-256, client-side, open source
- Free tier: 1 GB free forever
- Paid plans: From around $1.99/month for 20 GB (annual)
- Best for: technically-minded users who want independently auditable code
Limitation: no document-specific features; the product is primarily storage.
Comparison: encrypted document storage at a glance
| App | Zero-knowledge | Free storage | Doc features | Starting price |
|---|---|---|---|---|
| PrimeDocu | ✅ AES-256-GCM | 1 GB | ✅ Sign, scan, AI | Free / $9.99/mo |
| Tresorit | ✅ AES-256 | ❌ Trial only | Basic sharing | $12/user/mo |
| ProtonDrive | ✅ AES-256 + PGP | 1 GB (shared) | ❌ Storage only | $3.99/mo |
| Internxt | ✅ AES-256 | 1 GB | ❌ Storage only | ~$1.99/mo |
| Google Drive | ❌ Google holds keys | 15 GB | Basic | Free / $1.99/mo |
What about Google Drive and Dropbox?
Both Google Drive and Dropbox encrypt files in transit and at rest — but they hold the encryption keys. This means they can decrypt your files to power full-text search, AI assistants, and content scanning. They must also comply with valid legal requests for your data. For personal documents and work files that aren't sensitive, this trade-off is reasonable. For passports, medical records, legal documents, or anything you'd keep in a locked safe — zero-knowledge storage is the right choice.
Frequently asked questions
What is zero-knowledge encrypted storage?
Zero-knowledge means the storage provider cannot read your files. Encryption happens on your device before upload, and the key stays on your device. Even a hacked provider — or a court order — cannot expose your documents.
Is Google Drive encrypted?
Yes, but Google holds the encryption keys. It is not zero-knowledge. Google can read your files for search, AI features, and legal compliance. For truly private documents, use a zero-knowledge service like PrimeDocu or ProtonDrive.
What if I lose my phone — can I recover my files?
With PrimeDocu, yes — if you set a recovery password during setup. The password encrypts a backup of your device key. On a new device, enter your recovery password to restore full access to all your documents. We strongly recommend setting one.