Wiktionary
uncrackable
a. (context of a code English) That cannot be cracked; unbreakable.
Usage examples of "uncrackable".
Sometimes a little nudge brings an easy confession, sometimes it catalyzes uncrackable resolve.
The final southward flow crashed against that barrier line like the sea against an uncrackable breakwater.
The numbers were provided on demand from a central source, accessible by WormCam, rumored to be a random number generator buried in a disused mine in Montana, based on uncrackable quantum-mechanical principles.