The Australian Royal Mint has released a new batch of 50 cent coins with something of a secret mission.

These coins are being used to communicate an encrypted message, written in a code inspired by the Cold War events that led to the establishment of the Australian Security Intelligence Organisation (ASIO) 70 years ago.

The US Army Signals Intelligence Service was tasked with decoding encrypted Soviet diplomatic communications during the Second World War, as part of Operation Venona, which continued into the Cold War.

The Soviet intelligence service, the KGB, used a one-time pad system to code their messages, which should have been indecipherable.

But poor encryption practices meant some of the messages were able to be decoded.

Australia infiltrated by spies

While deciphering communications between KGB headquarters and their officers, US agents discovered a network of spies was running out of Australia.

It was a shock development which saw the US and Britain temporarily cut intelligence communications with Australia.

The UK urged the Australian government to form a national security service similar to its M15 to foil the Soviet espionage operation.

Prime minister Ben Chifley gave Justice Geoffrey Reed, a Supreme Court judge from South Australia, the first ASIO mission.

Mr Reed oversaw the drafting of a charter to specify the role and functions of what was to become ASIO, which was given special powers to protect Australia against espionage, sabotage and subversion.

In July 1949, a team of 15 were recruited as the first ASIO officers, being a group of legal experts, ex-military intelligence officers and former Commonwealth and state police personnel.

Their biggest priority was to eliminate the espionage threat — namely, to identify the members of the Soviet spy network.

Most of the work for the mission, which became known as "the Case", was done from the first ASIO headquarters in Potts Point, Sydney.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 3 minutes 8 seconds 3 m 8 s Australia infiltrated by Soviet spies 'without question', says academic given archive access

Cracking the code

Now, 70 years later, everyday Australians are being challenged to crack a code just like something those Cold War espionage agents would have grappled with.

The Mint has dubbed the mission Coincryption, which coincides with the release of the 2019 50c Uncirculated Coin, which is available in a limited mintage of 20,000.

Code breakers are being asked to decipher the message using a one-time pad system. ( US National Security Agency )

Code breakers have until December 2 to decipher the message using the one-time pad and conversion table included with the coin.

If they manage to decode the message, they submit their answer to the competition website to go in the draw to win.

The prize is the only proof commemorative coin in existence that features the 70th Anniversary of ASIO coin design.

The coin can be purchased from the Mint's website or by calling 1300 652 020.