Why Classical Certification is Impossible in a Quantum World
  We give a simple proof that it is impossible to guarantee the classicality of inputs into any mistrustful quantum cryptographic protocol. The argument illuminates the impossibility of unconditionally secure quantum implementations of essentially classical tasks such as bit commitment with a certified classical committed bit, classical oblivious transfer, and secure classical multi-party computations of secret classical data. It applies to both non-relativistic and relativistic protocols. 
Adrian Kent (Centre for Quantum Information and Foundations, DAMTP,   University of Cambridge and Perimeter Institute)