Law enforcement agencies like the FBI have long complained about what they call the "going dark" problem — the assertion that encrypted communications hamstring their efforts to catch criminals and terrorists. But US officials are only now reporting, for the first time, that encryption has managed to stop government wiretaps dead in their tracks.

Of the 3,395 wiretaps authorized by federal and state judges in 2012, investigators only failed to circumvent encryption in 4 of the 15 cases where they encountered it. The figures come from a new annual report to Congress from the US Administrative Office of the Courts, which has been tracking the use of encryption since 2000.

Previously, in the 109 reported cases between 2000 and 2011 where encryption was encountered, it had not fazed government wiretaps even once. It should be noted that the figures do not include any wiretaps authorized under foreign intelligence laws, which have been at the heart of the recent controversy over the NSA's ability to spy on innocent Americans.

The report comes as law enforcement officials continue to lobby for new legislation that would require internet communications software to be "wiretap-ready," a plan which security experts warn will force developers to intentionally make their software less secure. The new figures will likely renew calls to push the plan forward, but they are still a drop in the bucket when set against the dire warnings of law enforcement and the comparatively large number of cases where encryption was either ineffective or non-existent.