Conjugate variables in Quantum Key Distribution? According to Heisenberg's Uncertainty Principle, it is impossible to measure the values of conjugate variables simultaneously as measuring one accurately would make the other equally corrupt.

So in QKD, there's a thing that states that Eve can't eavesdrop as the very act would change it's quantum state(Heisenberg's principle). I would like to know the measurement of which conjugate pair is being referred to here. Do answer fast as I'll need to do a seminar on this topic tomorrow :)
In the simple BB84 protocol, Alice prepares a state in either the Hadamard or the Standard basis. In order to measure Eve need to choose a basis to measure in. The problem for Eve is these two are two orthogonal basis or in a sense "Conjugate". This however is not the same as the conjugate variables you mention in your question. 

Measuring in the one of the bases, collapses the state onto a vector in that basis. Measuring in an orthogonal basis would result in a truly random collapse onto a vector in this basis. Hence, no new information is gained about the original state. Thus Eve's choice of basis and the basis which Alice used to encode her bit in must match if Eve hopes to reliably learn Alice's bit.