Is it possible to run a "reverse" cryptcheck?

[nielash (Niel)]

Not exactly, but there are several pretty good workarounds to accomplish something similar:

1. Hasher backend -- effectively allows crypt to support checksums. See these recent threads for some tips and tricks.

2. rclone hashsum --download --output-file command, combined with check --checkfile. See this post.

3. The latest beta of rclone bisync has a new --download-hash feature that may be of interest.

4. The chunker backend can be used creatively as an alternative to hasher.

5. I actually built the exact feature you're talking about one time... but kind of abandoned the experiment after seeing how slow it would be to use!

@nielash

A few months ago I experimented with making a --crypt-sum flag to force crypt checksum support by generating them on the fly. It worked, but I didn't submit a PR because I figured the Hasher workaround was close enough, and also this would be impractical if you have several TBs of crypted data on cloud remotes (as I do). But your point about the decrypted filenames with hasher is a good one, and perhaps it's enough of a reason to revisit crypt providing hashes itself instead of requiring a (second) overlay. If you're interested, here was my branch that implements this. It is essentially the reverse the approach of "cryptcheck" (instead of re-encrypting the source, it decrypts the dest) which also means it still works when you don't have the source (like if you wanted to compare two different crypt remotes with different passwords.)

(6. I am also now working on something new which could be an interesting solution for this use case, when it's finished.)