Where does “ke- -an” come from?

ke- -an (Malay) comes from Proto-Malayic *kə- -an, from Proto-Austronesian *ka- -an.

ke- -an (Malay): ness; appended to adjectives to form nouns meaning "the state of (the adjective)", "the quality of (the adjective)", or "the measure of (the adjective)"