If you want to know how to keep 16,000 geeks entertained, ask the Lost Boy aka Ryan Clarke.

He's the cryptographer and puzzle master at Def Con, the huge annual international conference for hackers, taking place again in Las Vegas.

The fact that Def Con has a puzzle master at all is just one of the many reasons this conference is unlike any other.

Take the badges - which are circuit boards that the ingenuity of attendees turns into all manner of flashing, blinking gadgets.

Every other year the badges are part of a puzzle designed by Mr Clarke who, in his professional life, is a mathematician and engineer.

"This year I went analogue and I made a 7in record," said Mr Clarke.

For the benefit of younger readers a record is a dead media format that involved carving grooves on plastic that was then put on a turntable to be played.

"It was actually quite difficult to find someone that could manufacture this quantity these days because no-one is making records any more," he told the BBC.

The record bears a message that will help solve the bigger challenge, said Mr Clarke.

It's not the only place that extra information is available.

The different badges for attendees, press, staff, speakers and others all have different clues on the record label.

There are also clues on the lanyards that hold the badges.

"This causes people to go around the conference and they have to talk to each other in order to collect all the information to solve the puzzles and beat other people in the contest," said Mr Clarke.

One step ahead

Designing such a puzzle is hard, he said, because the idea is not simply to stump people with something that is impossible to solve.

"If I wanted to beat people I would just encrypt things and make it difficult that way," Mr Clarke said.

"It has to be fun and entertaining yet at the same time solvable which is a different problem space than most people are used to working in."

And, he said, he has to contend with all the online tools that people can turn to, in order to track down literary references, obscure books, mathematical ephemera and forgotten formulae.

"The puzzles and games I make for them have to be Google-proof and secure against all of the regular attacks otherwise its boring," he said.

"You have very brilliant people here, much smarter than I am, but I have to be constantly one step ahead of them with misdirection and the way I hide things."

Break-ins

To this heady cocktail of puzzles, maths, engineering, physics, linguistics and popular culture is added one more vital ingredient - complete freedom to tackle the challenge any way that people want.

"There are no rules," he said.

This breeds a lot of competition.

"They steal from each other, they break into my hotel room, they social engineer my family, they research my past, they look to where I went to school - I have complete profiles done on me every year," he said.

This year one keen team posted people all over Bally's casino on the Vegas strip on the lookout for Mr Clarke.

As soon as he was spotted they swooped and started pumping him for clues.

But trying to catch out the puzzle master at his own game comes with its own cost, because not all the information that can be gathered about Mr Clarke, or that he lets slip, is true or useful.

"I always lay a false trail. I have red herrings everywhere."

Free entry

There are some sweet rewards for the winners.

This year the person who completes the puzzle challenge gets an uber badge that has six radioactive isotopes embedded on a base known as a lichtenberg - acrylic etched by lightning.

And, said Mr Clarke, they get free entrance to Def Con for the rest of their life. Plus, and perhaps most importantly, bragging rights for being first.

The challenge for Mr Clarke is coming up with good puzzles every couple of years but, he said, it's necessary not just because people enjoy it.

"I do it because I believe that magic has been killed out of the world because you can get instant gratification through Google," he said.

"A kid today, if they see a magic trick that can instantly find out how it is done through the internet."

The Def Con puzzle challenge, he said, puts some of the magic back.