In which disciplinary category can cryptography be put?
It is multidisciplinary because it's a branch of mathematics and freely borrows from other branches such as statistics or algorithms.

I'm not so sure if it's cross-disciplinary. Although companies that make secure products (ie. products that use crypto facilities) employ cryptographers, cryptography in itself is a purely theoretical discipline that doesn't concern itself with implementation details that much (but Crypto.SE often does).

You could say it's interdisciplinary because it is a parent of quantum cryptography but I can't think of a justification for calling it cross-disciplinary.