Try and solve the puzzle by completing a series of letter sequences, then fill in your answers on the special Christmas bauble.

"Problem solving is at the heart of what we do. Taking on this Christmas cracker gives puzzlers an insight into the skills you need to be a GCHQ analyst," said a GCHQ spokesperson in a statement published Friday.

"Bring together a mix of minds by sharing it with the wise men and women in your household to find the solution."

The instructions are as follows: "Complete the following nine sequences and plot your single-letter answers in the corresponding golden nodes on the bauble. Follow the flow of the arrows from somewhere frosty to unlock a message."

The sequences are: GFEDCB_; NOHHPQ_; MDCLXV_; POIUYT_; DPLLMS_; HHELIB_; NAMWON_; EOEREX_; and GMRDPR_.

If you want to keep testing your skills, check out the GCHQ Twitter account, which publishes puzzles on a weekly basis.

The answer to the Christmas puzzle will also be posted on the account, as well as on Instagram and the GCHQ website.

GCHQ is an intelligence, cyber and security agency, according to its website. The agency is perhaps best known for its operations during World War II, when it relocated to Bletchley Park in Buckinghamshire.

There, code-breakers including Alan Turing famously decrypted coded German messages sent using the Enigma cipher machine.

More recently GCHQ was criticized by Big Tech for making a "ghost proposal" that would allow them to eavesdrop on encrypted messages.

At the end of 2018, high-ranking officials suggested service providers could "silently add a law enforcement participant" to encrypted group chats or calls.

But in May 2019 advocacy groups, security experts and tech giants including Apple, Google and WhatsApp signed an open letter to GCHQ demanding its spies be banned from accessing private digital messages.