Searching for a “secure file sharing service” returns dozens of options, all claiming to protect your data. But security claims are easy to make and hard to verify. Here are the specific features to look for — and the red flags that indicate a service is not as secure as it claims.

Must-Have Features

End-to-End Encryption

The single most important feature. Your files should be encrypted on your device before upload, with the decryption key shared only with the recipient. If the provider holds the keys, they can access your files — and so can anyone who breaches their servers.

Zero-Knowledge Architecture

This means the provider structurally cannot access your file contents. Not “we choose not to” — but “we are unable to.” This protects you from insider threats, legal compulsion, and server breaches simultaneously.

No Recipient Account Required

Every account a recipient creates is another credential that could be compromised. The most secure approach for external sharing is link-based downloads that work in any browser without sign-up.

Encryption Key in the URL Fragment

Look for services that embed the decryption key in the URL fragment (after the #). By HTTP specification, URL fragments are never sent to the server, which means the server never receives the key.

Nice-to-Have Features

• Download tracking — know when and whether a recipient accessed the file
• Link revocation — ability to disable a share link after the recipient has downloaded
• No file size limits — avoid services that cap uploads at 2GB or force file splitting
• Transparent documentation — the provider publishes details about their encryption implementation

Red Flags

Red Flag	What It Means
”Military-grade encryption” with no specifics	Marketing over substance
Provider can preview your files	They have access to unencrypted content
Password reset preserves file access	Provider holds your encryption keys
Files are searchable on the server	Server has access to file contents
Free tier requires extensive personal information	Your data may be the product

Frequently Asked Questions

Is open-source encryption software more secure?

Open source allows independent security researchers to audit the code, which builds trust. However, open source alone does not guarantee security — the implementation must also be correct and the software regularly maintained.

Do I need a VPN in addition to encrypted file sharing?

A VPN protects your network traffic. E2E encryption protects your files. They serve different purposes. If you are on public Wi-Fi, a VPN adds a useful layer of protection for your overall connection, but E2E encryption already protects the file contents regardless of network security.

Can the government force a provider to decrypt my files?

If the service uses true E2E encryption with zero-knowledge architecture, the provider cannot comply with decryption requests even if legally compelled — they do not possess the keys. This is by design, not defiance.