[EGreg]

Quantum cryptography would be fullproof. Any attempt to view the algorithm instead of using it would render it useless.

[cyphar]

That's not how quantum crypto works (it's based on observation of state, not the algorithm). Further, we've had cases of quantum crypto that just wasn't good enough to stop an observer from MITMing the internal state.

[squidbidness]

The usual expression is "fool proof", rather than "fullproof".