Two Oxford graduate students solved a so-called “impossible” puzzle – while enjoying their dinner at a popular Oxford eatery.

Freshly refurbished Japanese chain-restaurant Wagamama challenged customers to solve a complicated cipher written on its window, in honour of Albert Einstein’s birthday last month.

Oxford students Klaudia Krawiecka and Vojtech Havlicek solved it in one night over some teriyaki chicken.

The puzzle required the students to decode a sequence of numbers into letters of the alphabet, then into three words related to Wagamama.

Krawiecka, a first-year graduate studying cybersecurity at Keble, told the Oxford Mail: “We were having dinner at Wagamama when we found out about the competition.

“We had some spare time while waiting for the food and decided to give it a shot as we both enjoy solving puzzles.”

Kraweicka and Havlicek, who is pursuing a DPhil in quantum computing at Keble, were undaunted, with Havlicek saying that solving puzzles is the pair’s “daily bread.”

“We solve riddles on a daily basis in both personal and professional lives.”

First, they employed frequency analysis, an information security technique involving analyzing how often certain letters or numbers crop up in a cipher.

Krawiecka told Cherwell they “initially assumed that the most popular numbers in the sequence would denote the most common letters in the English alphabet.”

This led to a dead end, however, as the sequence was too short to apply the technique.

However, they then decided to break down the numbers into their constituent prime numbers. After that move, they noticed that each of the numbers in the puzzle was made up of a distinct set of prime numbers, prompting them to translate them into binary.

From there, they went to the American Standard Code for Information Interchange (ASCII) table, a standardized table for encoding information, and checked which binary numbers corresponded to which letters.

The puzzle’s answer was ‘Wagamama Ramen Teppanyaki’.

Wagamama rewarded the pair’s efforts with a £500 voucher to its restaurants. Havlicek said: “We will be well fed for a while!”