The U.S. National Security Agency will reportedly build a supercomputer that theoretically could crack most keys used for encrypted communications. According to documents provided by former NSA contractor Edward Snowden to The Washington Post, the effort to build "a cryptologically useful quantum computer" - a machine exponentially faster than classical computers - is part of a $79.7 million research program titled "Penetrating Hard Targets." Much of the work is hosted under classified contracts at a laboratory in College Park, Md., the report added.

The NSA declined to comment.

The basic principle underlying quantum computing is known as "quantum superposition," the idea that an object simultaneously exists in all states. A classical computer uses binary bits, which are either zeroes or ones. A quantum computer uses quantum bits, or qubits, which are simultaneously zero and one.

While a classical computer must do one calculation at a time, a quantum computer can sometimes avoid having to make calculations that are unnecessary to solving a problem.