The US government is looking at ways to prevent anyone spying on its own surveillance of Americans' phone records.
As the Obama administration considers shifting the collection of those records from the National Security Agency (NSA) to requiring that they be stored at phone companies or elsewhere, it is quietly funding research to prevent phone company employees or eavesdroppers seeing who the US is spying on, the Associated Press reports.
The Office of the Director of National Intelligence has paid at least five research teams to develop a system for high-volume, encrypted searches of electronic records kept outside the government's possession.
The project is among several ideas that would allow the government to no longer store Americans' phone records but still search them as needed.
Under the research, US data mining would be shielded by secret coding that could conceal identifying details from outsiders and even the owners of the targeted databases, according to public documents and AP interviews with researchers, corporate executives and government officials.
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The administration has provided only vague descriptions about changes it is considering to the NSA's daily collection and storage of Americans' phone records, which are presently kept in NSA databanks.
President Barack Obama this month ordered the attorney general and senior intelligence officials to recommend changes by March 28 that would allow the US to identify suspected terrorists' phone calls without the government holding the phone records itself.
One federal review panel urged Obama to order phone companies or an unspecified third party to store the records; another panel said collecting the phone records was illegal and ineffective and urged Obama to abandon the program entirely.
Internal documents describing the Security and Privacy Assurance Research project do not cite the NSA or its phone surveillance program.
But if the project were to prove successful, its encrypted search technology could pave the way for the government to shift storage of the records from NSA computers to either phone companies or a third-party organisation.
The NSA's surveillance program collects millions of Americans' daily calling records into a central agency database.
When the agency wants to review telephone traffic associated with a suspected terrorist - the agency made 300 such queries in 2012 - it then searches that data bank and retrieves matching calling records and stores them separately for further analysis.
