A couple of thoughts, the first of which was that he meant a toothed key. I looked up the word rasp, and the following could be interpreted to give some credence to this idea:
Part of Speech noun
Definition 1. a coarse file with conical teeth.
Similar Words file [2]
Definition 2. the act of rasping, esp. the act of scraping wood with a coarse file.
Synonyms scrape (1) , filing {file [2] (vt) }
Crossref. Syn. scratch , scrape
Similar Words excoriation {excoriate} , abrasion , gnash , scratch , grind
Definition 3. a rough, grating sound.
Synonyms scrape (1) , grating {grate [2] (vi 1)} , scratch (3)
Crossref. Syn. scratch , scrape , grind
Similar Words screech , creak , squawk , stridulation {stridulate} , squeak , croak , grind
Related Words gnash , creak , abrasive wordsmyth My other thought was that if arruginated means raspy, maybe it could have been intended as a kind of synonym for rusty; that is, it would seem to make sense that if a key is rusty, it will make a rasping sound in the lock. [shrug]
