One very "brave," very dead bird from the Second World War has been trying to tell a story for almost 70 years. Yet some of today's sharpest mathematical minds are finding it impossible to decode the message.

This enigma of a spy story started years ago, after a British citizen on the outskirts of London renovated an unused fireplace. Inside, he found the bones of a military carrier pigeon, one with a red aluminum spool still strapped to its leg.

During the 1940s, most likely on D-Day, the exhausted bird had journeyed from Europe's battlefields before the chimney had somehow become his final resting place. Inside the pigeon's red spool was a letter scrawled on very thin paper, written on British military letterhead, and signed by one "Sjt. W Stot."

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The sergeant's coded message contains 27 five-character sequences – "AOAKN HVPKD FNFJW YIDDC …" – that would seem to be complete gibberish, but which were actually an encrypted message for military commanders.

Once passed along to government authorities, the message ended up in the hands of an ultra-secretive British spy agency for analysis. Last month, this agency publicized the case with a rare public statement – including an admission that it was completely stumped by the correspondence and needed help figuring it out.

"Without access to the relevant code books and details of any additional encryption used, it will remain impossible to decrypt," Britain's Government Communications Headquarters (more familiarly, GCHQ) said in a November statement.

"… Although it is disappointing that we cannot yet read the message brought back by a brave carrier pigeon, it is a tribute to the skills of the wartime code-makers that, despite working under severe pressure, they devised a code that was undecipherable both then and now."

Many observers took the admission as a challenge. One Canadian senior citizen has, in particular, garnered publicity for claiming he cracked the code.

"It annoyed me when they said it's too complicated to figure out," Gord Young, a 70-year-old military buff from Peterborough, Ont., said in an interview. "All these people saying it can't be cracked. Dammit it all, it can be cracked."

Mr. Young claims he managed the feat inside of 17 minutes – but this is highly contentious. GCHQ will not endorse his findings, nor any of the dozens of other submissions it has received from the public in recent weeks.

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GCHQ (like the U.S. National Security Agency and Communications Security Establishment Canada) is a spy agency that employs scores of PhD-calibre mathematicians and computer scientists. These career code-crackers have access to unfathomably powerful computers as they work to crunch numbers during complex calculations.

Governments pay handsomely for this "signals-intelligence" or "SigInt" security work, which dredges up deeper meaning from the ceaseless chatter of the digital world.

"SigInt" can guard against foreign hackers who, while working for hostile states, have emerged as an espionage threat to Western governments and corporations. "SigInt" agencies also work to mine and map out torrents of telecommunications, including encrypted e-mails, in order to help governments forecast terrorist threats.

Yet there is apparently no modern algorithm that can decode a message from an ossified pigeon. In the 20th century, soldiers often used "one-time pads" to encrypt their messages. The only people who could read the correspondence were fellow soldiers, who also had ciphers for the one-off codes.

During the Second World War, the British enlisted some 250,000 carrier pigeons to cart coded messages from continental Europe to London and back – an effective end run around the electronic eavesdropping the Nazis were conducting against any radio signals.

Countermeasures for this, too, emerged over time. "Hawk patrols," for example, are said to have pitted peregrines against pigeons in this unheralded aerial battle in Europe.

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Affiliated with a group of Peterborough volunteers known as Lakefield Heritage Research, Mr. Young was feted in the British papers this month for allegedly one-upping GCHQ. His work was first profiled in the Peterborough Examiner late last month.

Mr Young has since written to the Canadian War Museum and even to British Prime Minister David Cameron to tell them he had figured out the message.

He was never himself a military man. But he did dig out his great uncle's First World War code book, to help understand a series of possible acronyms used in the Second World War's carrier-pigeon correspondence.

By his reasoning, "AOAKN" in the coded message means "Artillery Observe At K [Sector] Normandy," and "HVPKD" means "Have Panzers in K [Sector] Determined," and so on.

By his logic, the message amounts to a 1944 battlefield warning to British commanders about a powerful tank assault in Normandy. He did more digging, and figures the message was sent by British Fusilier William Stott, a 27-year-old from Lancashire killed in 1944 – just a few weeks after the message was sent to England.

"This guy was a damn hero," said Mr. Young, who thinks the soldier deserves a medal.

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He's also in awe of the pigeon. How would a bird that had never been to France know to take a message back to England?

Scientists say that bird brains have the power to navigate the Earth by picking up on variations in magnetic fields. It's a powerful ability. Just imagine your own brain had a built-in precursor to today's geolocating global-positioning system (GPS), where satellites tell your smartphone precisely where you are at any given moment.

These days, GCHQ and other "SigInt" spy services routinely tap into satellite signals, smartphones and Internet infrastructure to crack codes in hopes of pinpointing precisely where the biggest threats to national security may lie.

But no electronic eavesdropping can answer the riddle posed by a bird that collapsed into a chimney almost 70 years ago.

"GCHQ has followed with interest the media reporting on the possible solutions to the encoded message found on the dead pigeon," a spokesman for the agency told The Globe and Mail on Monday.

Speaking from London, he declined to give his name and said he would not comment on any individual effort to crack the code – except to say that all submissions received by GCHQ to date are wrong.

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"Hundreds of those proposed solutions, we've carefully examined them, by our expert cryptanalysts. And so far none of them have proved credible," he said.

The mystery of the pigeon remains.