Clearsigned against detached
An announcement arrives in one of two shapes, and the verification command differs slightly between them. Knowing which you are holding avoids most of the confusion at this step.
Clearsigned
The message and the signature travel together in one block, with the readable text in the middle between two markers. This is the common form for a rotation post, because it can be read by somebody who never verifies anything and still checked by somebody who does.
Detached
The signature lives in a separate small file alongside whatever it signs. This is the form used for downloads, where you do not want a signature block wrapped around a binary. Verifying it means naming both files in the command.
The copy and paste trap
A clearsigned block is verified byte for byte, including the whitespace. Anything that reflows lines, converts straight quotes into typographic ones, strips trailing spaces or adds a wrapper will break a perfectly valid signature. Messaging clients and rich text editors all do at least one of those.
- Save the block to a plain text file rather than pasting it through anything clever.
- Include the marker lines at the top and the bottom, both of them.
- Do not correct spacing that looks wrong, because it is not wrong.
A broken signature is not the same as a bad one
A failure caused by mangled whitespace and a failure caused by a forged message look similar at a glance and mean completely different things. Before concluding an announcement is fake, fetch the block again cleanly and verify the fresh copy. Most first failures are transport damage.
What each form proves
Both prove the same two things: the message came from the holder of a specific private key, and not one byte has changed since it was signed. Neither proves the contents are true, which is a separate question a signature was never designed to answer.