## Four levels

Four levels of increasing difficulty: From pen & paper to complex mathematical problems.

## Limited attempts

You have only a limited number of attempts to solve each challenge. Be certain of your answer before you submit it.

## Be fast

Be fast and earn a place on the Hall of Fame. The first four to solve each challenge will be displayed permanently.

## Special Level X

The special level X contains cryptographic problems which are currently not known to have been solved.