David Huerta, an artist and software engineer has sent an encrypted mixtape to the NSA which he says they will never be able to crack. Huerta made the tape as a response to the NSA's publishing of Edward Snowden's documents online and after the NSA's surveillance programs and their attempts to weaken encryption were revealed in 2013. Huerta's mixtape apparently includes musical tributes to Laura Poitras and Glenn Greenwald, who were instrumental in helping to publish Snowden's documents.

Read more: NSA successfully targets anyone with a passing interest in TOR

To record his mixtape, Huerta covered an Arduino electronics board in transparent acrylic - perhaps symbolic of the actions that lead him to be called a whistleblower - and stored the music on an encrypted SD card, which only he has the password for. He then sent the package to the NSA's headquarters in Fort Meade, MD.

Revealing his motives, Snowden supporter Huerta wrote a post on his blog in May: "Encryption is the blind spot to the NSA's all-seeing eye," he said. "Math doesn't need an information dominance center to enforce its rules. Math is the legal framework which the universe can only obey and will trump and outlast the rules of any human state."

Traditionally, the NSA have worked around encrypted documents by finding a weak link elsewhere in the system and working from there.

Read more: The year the NSA hacked the world: A 2013 PRISM timeline

Though Huerta has kept the tracklist and musical direction on his encrypted mixtape close to his chest, he had one last message for the NSA on his blog. "The NSA can read my stupid Facebook updates but without my consent it will never be able to listen to my kick-ass mixtape," he wrote.