  Mistrustful cryptography includes important tasks like bit commitment,
oblivious transfer, coin flipping, secure computations, position
authentication, digital signatures and secure unforgeable tokens. Practical
quantum implementations presently use photonic setups. In many such
implementations, Alice sends photon pulses encoding quantum states and Bob
chooses measurements on these states. In practice, Bob generally uses single
photon threshold detectors, which cannot distinguish the number of photons in
detected pulses. Also, losses and other imperfections require Bob to report the
detected pulses. Thus, malicious Alice can send and track multiphoton pulses
and thereby gain information about Bob's measurement choices, violating the
protocols' security. Here, we provide a theoretical framework for analysing
such multiphoton attacks, and present known and new attacks. We illustrate the
power of these attacks with an experiment, and study their application to
earlier experimental demonstrations of mistrustful quantum cryptography. We
analyse countermeasures based on selective reporting and prove them inadequate.
We also discuss side-channel attacks where Alice controls further degrees of
freedom or sends other physical systems.
