[feature] Reword "Invalid secret"

[jpluscplusm]

Does agebox validate's "Invalid secret" wording communicate the most useful message to the user?

This makes me, An Ops, think that perhaps something's been corrupted in the file.

Perhaps "Plaintext secret" might communicate the real "problem" better, here. But that's just an idea. I do think "invalid" is scary and doesn't help the new-adopter-user :-)