Cryptomator holds a narrow lead over Sync as a client-side tool for adding encrypted vaults to existing cloud accounts. When buyers ask for client-side encryption where the provider cannot know their password, Proton Drive is the usual answer.
Since July, AxCryptrising has become one of the most named choices for encrypting files before emailing clients, while VeraCryptfalling is named occasionally. Across the market, SpiderOakfalling, VeraCryptfalling, and GnuPGfalling have seen reduced visibility.
Latest insights
Week of Sep 21–27 · Since Jul 5
Proton Drive Gap between platforms: Proton Drive's Mentioned in is higher on ChatGPT Search than on Google AI Mode in Secure Encrypted Cloud Storage: 62.6% vs 43.6%
pCloud Gaining: pCloud moved up 1 place to rank #2 of 72 in Secure Encrypted Cloud Storage
Dropbox Gap between platforms: Dropbox's platform gap in Secure Encrypted Cloud Storage widened: ChatGPT Search 39%, Google AI Mode 26.5%
Dropbox Slipping: Dropbox dropped 1 place to rank #3 of 72 in Secure Encrypted Cloud Storage
Dropbox Slipping: Dropbox now trails pCloud in Secure Encrypted Cloud Storage, #3 to #2
If your main requirement is that the cloud storage provider must never have access to your decryption keys, look for a service with true zero-knowledge, end-to-end encryption (E2EE). That means your files are encrypted on your device before upload, and the provider stores only encrypted data—not a usable key to read your files.
My top recommendations are Proton Drive for personal use and Tresorit for business or sensitive documents. Both explicitly document zero-knowledge encryption.
Best cloud storage providers for zero-knowledge encryption
For a firm storing sensitive files in the cloud, which encryption and key management solutions are practical without enterprise budgets?
What's a good, easy-to-use tool for encrypting sensitive files before we email them to clients?
1. Proton Drive
(Best overall for personal use)
Files and filenames are protected by end-to-end encryption. Proton says it cannot read your files, and its apps are open source, allowing independent inspection.
Best for: documents, photos, personal backups and everyday file sharing.
Key consideration: account recovery and key management still matter; don't assume the provider can recover every lost encryption secret.
Website:
2. Tresorit
(Best for business)
Tresorit encrypts files on your device and says encryption keys remain under user control, not accessible to its servers. It also emphasizes secure collaboration and business compliance.
Best for: confidential business files, client documents and team collaboration.
Key consideration: compare plan pricing and administrative features before committing.
Website:
3. Sync.com
A strong alternative to compare if you want private cloud storage with file synchronization and sharing. Its zero-knowledge model is designed to prevent the provider from reading file contents.
Best for: cloud backup, file sharing and everyday storage.
Key consideration: check recovery, sharing and device-support details against your workflow.
Website:
What to check before choosing
Security requirement
What to look for
Provider cannot decrypt files
End-to-end encryption by default
Provider does not hold your keys
Keys generated and used on your device
Filenames are private too
Encrypted filenames and folder metadata
Protection against account takeover
Two-factor authentication or security keys
You can recover your files
Documented recovery process that doesn't give the provider decryption access
One important caution: zero-knowledge encryption does not necessarily hide all metadata, such as access times or account details. Also, losing your recovery information can mean permanently losing access to your files.
My recommendation: Start with Proton Drive if you're an individual who wants strong privacy without having to manage encryption manually. Choose Tresorit if you need more business-oriented controls.
To narrow this down, how much storage do you need?
What you're looking for is zero-knowledge cloud storage with client-side encryption. Your files are encrypted on your device before being uploaded, and the provider doesn't have the keys needed to read them. Ideally, the provider also cannot recover your encryption keys using your account password.
My first recommendation is Proton Drive. It encrypts files on your device, uses end-to-end encryption, and says that even Proton cannot decrypt your stored files.
Best cloud storage options
1. Proton Drive — Best overall
(Best starting point)
Client-side, end-to-end encryption by default.
Proton cannot decrypt your stored files.
Open-source apps and published security audits.
Free plan with 5 GB of storage.
Best for everyday file storage, documents, photos, and backups.
There are two different things a provider might mean by "password":
Account login password: used to authenticate you.
Encryption key or recovery secret: used to decrypt your files.
Your requirement is that the provider cannot access your files even if it has your account records or a copy of its server database. A zero-knowledge design helps achieve this. However, account recovery features, compromised devices, and malicious or modified client software are still worth considering.
My recommendation: Start with Proton Drive for simplicity, or use Cryptomator with a cloud provider you already have if you want independent control over encryption.
One question to narrow this down: Do you want automatic syncing across your computer and phone, or is this mainly for securely storing files and accessing them occasionally? That makes a meaningful difference in which service I'd choose.
When you need true zero-knowledge privacy—meaning files are encrypted client-side on your device and the provider never sees your password or keys —you must avoid mainstream options like Google Drive, Dropbox, or OneDrive.[](https://shieldfive.com/resources/best-zero-knowledge-cloud-storage)
The top cloud storage providers that use out-of-the-box client-side zero-knowledge encryption (where losing your password means losing access to your data forever, as they cannot reset it) include:
Sync.com : Features zero-knowledge encryption by default on all plans. Files are encrypted locally before they leave your device, and the company has no technical means to read your files or recover your password.[](https://shieldfive.com/resources/best-zero-knowledge-cloud-storage)
Proton Drive : Built with zero-access architecture from the team behind Proton Mail. It provides end-to-end client-side encryption for files, file names, and folder structures, backed by strict Swiss privacy laws.[]()
What you're looking for is a zero-knowledge, end-to-end encrypted (E2EE) file-syncing service. The key requirement is that files are encrypted on your device before upload, and the provider cannot access the decryption keys or read your stored files.
One important distinction: encryption in transit and encryption at rest aren't enough. Many cloud-storage providers encrypt files on their servers but retain the keys themselves. You want client-side encryption, with keys controlled by you.
Here are the services I'd investigate first, with an emphasis on genuine privacy rather than just secure file transfers.
My top recommendations
1. Proton Drive
(Best overall starting point)
A good choice if you want a straightforward cloud drive with automatic desktop syncing and end-to-end encryption. Proton says files are encrypted on your device before syncing, so Proton itself cannot read their contents.
Best for: personal files, documents, and everyday multi-device use.
A mature file-syncing and sharing service built around zero-knowledge encryption. Its documentation says encryption keys stay under user control, and desktop sync keeps local folders synchronized with the cloud.
Best for: confidential documents, business files, and controlled sharing.
A cloud storage service advertising end-to-end encryption, zero-knowledge protections, automatic syncing, and file recovery. It's worth comparing if you want a conventional cloud-drive experience.
Best for: everyday cloud storage, backups, and sharing.
Rather than being a cloud provider, Cryptomator encrypts files locally in a vault that you can store in Dropbox, OneDrive, Google Drive, or another syncing folder. It encrypts file contents and names before the cloud provider receives them.
Best for: keeping your existing cloud service while adding a separate layer of client-side encryption.
Trade-off: you manage the vault and its password, and some workflows are less seamless than an integrated encrypted drive.
Recovery: If you lose your password or recovery key, can you recover your files? Strong zero-knowledge systems may be unable to help.
Metadata: File contents may be encrypted while some information, such as account details, file sizes, or access times, remains visible.
Sync behavior: Confirm the desktop app supports the folders and operating systems you need.
Independent verification: For especially sensitive files, look for independent security audits and transparent encryption documentation.
Let me narrow it down
1. Which devices do you need to sync?
Windows + Android
Windows + iPhone
Mac + iPhone
Linux + other devices
Multiple computers
2. How much storage do you need?
Under 100 GB
100–500 GB
500 GB–2 TB
Over 2 TB
3. What's your budget?
Free only
Under $10/month
$10–20/month
Flexible for stronger privacy
4. What's most important?
Easy automatic sync that just works
Maximum control over encryption keys
Open-source software
Secure sharing with other people
[Find my best fit]
My initial shortlist would be Proton Drive for simplicity, Tresorit for security-focused collaboration, and Cryptomator if you want more direct control over the encryption layer.
The key is to find a service that meets both requirements:
Block-level sync: When you change a small part of a large file, only the changed blocks are uploaded, rather than the entire file.
No content scanning: The provider cannot inspect your files for their contents, ideally because files are encrypted on your device with keys the provider doesn't possess.
These requirements can conflict. End-to-end encryption can prevent a cloud provider from reading your files, but some privacy-focused services sacrifice block-level sync because of their encryption architecture.
Best options to consider
1. Dropbox + Cryptomator
My first option to investigate if you need both features. Dropbox is known for block-level synchronization; Cryptomator encrypts files locally before they enter the cloud, so Dropbox receives encrypted data instead of readable document contents. This can give you a practical combination of efficient sync and privacy, though you should test how your specific large files behave.
Trade-off: two applications, and Dropbox still sees some account and file-transfer metadata.
A better fit if privacy is the priority. Sync.com advertises end-to-end encryption designed to prevent the provider from reading your files. However, it does not offer block-level deduplication, so it does not satisfy both requirements.
A strong alternative for private storage. Proton says files are encrypted on your device and cannot be read by Proton. It splits large files into 4 MB chunks for encrypted transfer, but that is not proof of block-level delta sync—only changed blocks being uploaded after an edit.
Start by evaluating Dropbox with a Cryptomator vault, but verify that it transfers only changed blocks for the specific file types and applications you use. Dropbox documents delta sync, while Cryptomator encrypts file contents and names locally.
One important caveat: encryption alone does not guarantee efficient delta sync. If an application rewrites an entire large file, many or all encrypted blocks may change, increasing upload traffic.
One question to narrow this down: Do you need block-level sync mainly for large files that change slightly (such as virtual-machine disks, databases, or Outlook PST files), or for ordinary documents and photos? That distinction can change the best recommendation.
To perform block-level sync , a cloud provider's server or sync algorithm must inspect, compare, and index the internal chunk hashes or byte-segments of your files to figure out what changed. If the provider cannot read or look inside your files because they are encrypted client-side with a key they don't possess (zero-knowledge), they cannot mathematically calculate or perform block-level deduplication/syncing on those chunks.[](]()](]()]()
NordLocker : Focuses entirely on local and cloud-based zero-knowledge encryption using AES-256 and XChaCha20 algorithms before files sync to their servers.
If you want to use standard cloud storage (like Google Drive or Dropbox) or local networks while maintaining absolute key ownership, use these client-side tools:
Cryptomator: Free, open-source tool that creates a transparent client-side encrypted vault inside your existing cloud sync folder (Dropbox, Google Drive, iCloud, etc.) using AES-256.
Proton Drive: Focuses heavily on open-source, zero-knowledge architecture with end-to-end encryption for files, though it uses traditional file sync/upload mechanisms rather than delta block-level sync.
pCloud: Supports efficient block-level data syncing (uploading only changed parts of a file). Standard pCloud storage does not encrypt data client-side by default. However, you can add pCloud Crypto , a paid add-on that creates a client-side, zero-knowledge encrypted folder on top of their infrastructure. Keep in mind that applying zero-knowledge encryption to specific folders restricts how block-level delta sync behaves on those specific secure compartments.[](https://cloudstorageinfo.org/tresorit-review)[[2](https://cloudstorageinfo.org/block-level-file-sync)](https://gizmodo.com/best-cloud-storage/pcloud-vs-sync)
Would you prefer to lean toward strict zero-knowledge privacy (and compromise on file-level syncing), or do you have a specific file size/workflow issue (like syncing large databases or disk images) that makes block-level sync mandatory?
