In room-size metal boxes, secure against electromagnetic leaks, the US National Security Agency is racing to build a computer that could break nearly every kind of encryption used to protect global banking, medical, business and government records. According to documents provided by former NSA contractor Edward Snowden, the effort to build "a cryptologically useful quantum computer" - a machine exponentially faster than classical computers - is part of a US$79.7 million research programme entitled "Penetrating Hard Targets". The development of a quantum computer has long been a goal of many in the scientific community. It would have revolutionary implications for fields such as medicine as well as for the NSA's code-breaking mission. With such technology, all forms of public key encryption would be broken, including those used on secure websites and those used to protect state secrets. Although the full extent of the NSA's research remains unknown, the documents provided by Snowden suggest that it is no closer to success than others in the scientific community. "It seems improbable that the NSA could be that far ahead of the open world without anybody knowing it," said Scott Aaronson, an associate professor of electrical engineering and computer science at the Massachusetts Institute of Technology. The NSA appears to regard itself as neck and neck with labs sponsored by the EU and the Swiss government, with steady progress but little prospect of an immediate breakthrough. "The geographic scope has narrowed from a global effort to a discrete focus on the European Union and Switzerland," one NSA document states. The documents indicate that the NSA carries out some of its research in large, shielded rooms known as Faraday cages, which are designed to prevent electromagnetic energy from coming in or out. Those, according to one brief description, are required "to keep delicate quantum computing experiments running". Quantum computers have many applications for today's scientific community, including the creation of artificial intelligence. But the NSA fears the implications for national security. "The application of quantum technologies to encryption algorithms threatens to dramatically impact the US government's ability to both protect its communications and eavesdrop on the communications of foreign governments," according to a document provided by Snowden.