Verify and integrity

A file is complete only when it is proven complete

When the last block arrives, Rapidly does not just trust the byte count. It checks the file again from the disk, and compares it with a checksum if you gave one (or the server gave one). Only then does the download show as complete.

Checksums

In Advanced you can paste the expected checksum (MD5, SHA-1, SHA-256 or SHA-512). If the finished file does not match, the download is marked "Needs attention" and the file is kept so you can look at it. Rapidly never silently deletes a file that failed a check.

The integrity root

For every download Rapidly also keeps a short fingerprint built from the fingerprint of every block (a Merkle root). Two copies of the same file give the same root, and a change in any single block changes it. This is what lets Rapidly find exactly which block is damaged instead of downloading everything again.

Integrity proof export

On a finished download you can export an integrity proof: a small file that records the address, the size, the checksum and the integrity root. Anyone can use it to check that a copy of the file is the same.

Portable bundles: resume on another PC

You can export an unfinished download as a bundle and import it on another computer. The new computer asks the server whether the file is still the same one, and continues from the blocks that are in the bundle.