The best of the British code breakers have apparently met their match in a WWII-era secret message recently discovered attached to the leg of a long-dead pigeon.

Cryptographers at Britain's Government Communications Headquarters (GCHQ), the spy agency in charge of signals intelligence, have been analyzing the short handwritten message for weeks but threw up their hands Friday, saying it will be impossible to decode "without access to the original cryptographic material."

The note, written on official stationary with the heading "Pigeon Service," was discovered in a red canister attached to the skeletal leg of a pigeon in a chimney in Surrey. The message is made up of 27 seemingly random five-letter blocks and though it's undated, government analysts believe the pigeon met his end while on a secret mission during the Second World War. The note is signed "Sjt W Stot" and was intended for the destination "XO2."

In a statement released overnight, the GCHQ said that during the war, secret communications would often utilize specialized codebooks "in which each code group of four or five letters had a meaning relevant to a specific operation, allowing much information to be sent in a short message." The GCHQ said that those messages may have been put through an additional layer of security by being re-coded with what's known as a one-time pad.

One-time pads make up a theoretically uncrackable secret communications system in which an agent could encode a message using a key that uses truly random numbers to translate plain text into what looks like jibberish. The recipient of the coded message would then only be able to decode the message if they possessed an identical key. After a single use, both keys would be destroyed.

"This means that without access to the relevant codebooks and details of any additional encryption used, it will remain impossible to decrypt," the GCHQ said.

Nearly a quarter million carrier pigeons were used during the Second World War by various branches of the British military including Britain's Special Operations Executive, according to the GCHQ. In the air, the small birds fought their own version of the war, braving enemy hawk patrols and soldiers on the ground taking potshots.

The GCHQ has enlisted the Pigeon Museum at Bletchy Park to trace the identity of the pigeon - each was given a service number - but is still seeking information on what "Sjt W Stot" and "X02? could tell them about the note's origin and purpose. Was it vital information about the secret D-Day invasion plans? Was it nothing but a training exercise?

One GCHQ historian told BBC News the most helpful suggestion came from the public already:

"A member of the public… suggested that, since the message was found in the chimney, the first two words are most likely to be 'Dear Santa,'" the historian said.