Blue Bossa is in the key of C minor.
The main chords Cminor9 and Fminor9 and the jazz cadence Dm7(b5) to G7 are all diatonic chords. The melody is also a simple sequence of notes from the minor scale, brought to life primarily by its rhythmic properties.
The exception is a brief shift in the chord progression to Db major in bars 9-13.