BitSeal — proof the file is unchanged
What the BitSeal badge on the download page means, and what it doesn't protect against.
BitSeal is a Pro feature. Every file in a transfer gets a sealed fingerprint, and the recipient sees a BitSeal badge next to the file on the download page.
What happens when you send
While the file is being encrypted on our server, we calculate a SHA-256 fingerprint of its content. The fingerprint is sealed with a key only our servers hold, and stored with the transfer.
What the recipient sees
When the download page opens, we check the seal. If it holds, the BitSeal badge appears next to the file. If it doesn't — for example because someone changed the fingerprint in the database without the key — the badge is not shown.
The file itself is also encrypted in parts with authenticated encryption (AES-256-GCM). If any of the stored bytes have been changed, the download stops instead of delivering altered content.
What BitSeal doesn't protect against
- Changes before the file reached us. The fingerprint is calculated on our server after upload, not on your machine.
- Someone with full control of our servers. With both the database and the key, a seal can be made again.
- Harmful content. BitSeal says the file is the same one that was uploaded, not that it is safe. Virus scanning checks that, and it applies to every transfer.