uncheatable

un- +‎ cheat +‎ -able.

uncheatable (not comparable)

1. Not subject to cheating, impossible to cheat (at).
   • 2002, George W. Barlow, The Cichlid Fishes: Nature’s Grand Experiment In Evolution, Da Capo Press, →ISBN, page 100:

     Amoz Zahavi^[sic] argued, however, that natural selection should favor signals that cannot be cheated.³² Uncheatable signals carry a cost, a handicap.

   • 2005, Song Han, Elizabeth Chang, Jie Wang, “Attack on Undeniable Partially Blind Signatures”, in Andrew Blyth, editor, EC2ND 2005: Proceedings Of The First European Conference on Computer Network Defence, School Of Computing, University of Glamorgan, Wales, UK, Birkhäuser, published 2006, →ISBN, page 143:

     We show that the signer can disavow any valid signature to the verifier. In other words, we show that the disavowal of their scheme is not uncheatable.

• unteachable