How to send large files securely (without WeTransfer)

The two problems in one task Sending a 40 GB master involves two separate problems. Reliability: the upload has to finish over an imperfect connection. Confidentiality: the file should not be readable by the service in the middle. Most tools solve one and ignore the other.

Step 1 — Stop using email attachments Attachments create permanent, readable copies on mail servers, in backups and in the recipient's client, and they cannot be withdrawn. For anything confidential, a revocable link beats an attachment every time, regardless of size.

Step 2 — Encrypt before the upload, not after "Encrypted transfer" usually describes TLS, which protects the network path and nothing else. What matters is whether the file is encrypted on your device before the first byte leaves it. If key generation happens on a server, the server can read the file.

Step 3 — Use a resumable, chunked upload Large transfers fail for mundane reasons: a lift, a hotel network, a laptop lid. Chunked resumable uploads let the transfer continue where it stopped. This is a security control as much as a convenience one, because a failed transfer at 11pm is what makes someone upload the master to a personal cloud account.

Verification after upload matters too: authenticated chunks are checked so you know the stored copy matches what you sent.

Step 4 — Split link and passphrase across channels Send the link by email and the passphrase by phone, SMS or a different chat app. An attacker who reads one mailbox then has half of nothing. It takes ten seconds and removes most realistic interception paths.

Step 5 — Keep the exposure window short Set the shortest expiry that works for the recipient. Public links here expire within 24 hours at most and can be revoked instantly. Cap the number of views when you can, and use one link per recipient so revocation is surgical and the access log means something.

Step 6 — Watermark review material When the recipient needs to read the file rather than keep it, per-viewer watermarking makes a screenshot traceable to a person. It does not prevent capture; it changes the incentive.

Step 7 — Decide where the file lives afterwards Transfer services forget. If the file will be needed again, put it in an encrypted drive and re-share from there instead of re-uploading a 40 GB master.

A checklist you can reuse - Encrypted on the device before upload - Chunked, resumable, verified upload - Passphrase on a separate channel - One link per recipient, shortest workable expiry - Watermark for review-only material - Revoke when the project closes - Archive the file somewhere encrypted