A private download URL can keep strangers from finding a file, yet the storage provider may still be able to read its contents. That is not the same promise as end-to-end encryption. If you are sending a medical record, unreleased design or sensitive contract, the difference matters more than a colorful “secure” badge.
I checked the current security documentation for two practical options on 25 September 2026. This is a comparison of documented encryption models and workflows, not an independent cryptographic audit or a large-file speed test.
What end-to-end encryption means
With a properly implemented end-to-end encrypted service, the file is encrypted on the sender's device and decrypted on an authorized recipient's device. The service handles encrypted data but should not have the content-decryption key. The exact claim depends on how link secrets, account recovery and browser code are implemented.
TLS protects data while traveling between your browser and a server. Ordinary at-rest encryption protects a storage system against certain disk risks. Neither alone means the provider cannot access a file. I would read the product's security design, not infer E2EE from a padlock icon.
Wormhole for a short-lived send
Wormhole describes client-side encryption for its transfer flow. Its FAQ says files up to 5 GB are stored for 24 hours, while files above 5 GB use peer-to-peer delivery. The public uploader says “send up to 10 GB.” Those two thresholds describe different mechanisms, not a 5 GB contradiction.
For a time-sensitive handoff, I would test the exact link with the recipient before shutting the sending device. Peer-to-peer delivery of a larger file may need both parties online together. The 24-hour server deletion window is useful, but it also means a late recipient can miss the transfer.
Proton Drive for ongoing access
Proton Drive describes end-to-end encrypted storage. Its sharing guide explains public links, viewer or editor permissions, optional link password and expiry. A recipient can open a public link without a Proton account, but the link is still associated with the sender's account.
This fits a file that needs to stay available or a folder that may change. Storage quota matters: a maximum supported file size is not your free storage allowance. For a sensitive link, I would set an expiry and send an optional password by a separate channel rather than put the link and password in the same message.
Where this site fits
Big File Sharing uses TLS in transit and private, non-public transfer links, as described on our security page. We do not claim the current transfer system provides end-to-end encryption or zero-knowledge storage. If only the intended recipient must be able to decrypt file contents, choose an E2EE product or encrypt the file yourself before uploading.
Our guest upload is convenient for a first short-lived private handoff, and later temporary sends remain free with an account. It is not a substitute for a provider whose cryptographic design meets your threat model.
How to choose safely
First decide who you must protect the file from: casual link guessing, a forwarded email, a compromised service account or the service operator. Then inspect where encryption happens, who holds the key, whether links carry a secret, and what recovery options exist. Strong encryption cannot fix sending the link to the wrong person.
Second, test the receiver workflow. Open the link on a separate device, verify expiry and password behavior, and download the original file. Compare a SHA-256 hash if byte integrity matters. I also check whether the recipient needs a new account, because signup friction can derail an urgent handoff.
Common questions
Is a password-protected link E2EE?
Not automatically. A password can restrict access while the provider still holds the file's decryption key. Look for a clear, current explanation of client-side encryption and key handling, not just a password field.
Can I email an encrypted file link?
Yes, but anyone with the full link and any required password may be able to open it. For sensitive files, confirm the recipient address, limit link lifetime and send a separately chosen password through another channel.
Does E2EE guarantee anonymity?
No. A service may still know account identity, IP addresses, timing, file sizes or who shared a link. Proton explicitly notes that its public sharing is not anonymous. Read each provider's privacy details if metadata exposure is part of your concern.
