furtive

Synonyms: artful calculating cautious circumspect clandestine cloaked conspiratorial covert crafty creepy cunning disguised elusive evasive foxy guileful hidden hush-hush insidious masked scheming shifty skulking slinking sly stealthy subrosa surreptitious tricky undercover underhand underhanded under-the-table under wraps wily

Antonyms: aboveboard forthright honest open truthful