Related Clues:

• Brain twister
• Puzzling person/thing
• It's a mystery why one might read Hemingway
• Mind-boggling puzzle
• Encryption machine featured in 'The Imitation Game'
• German cipher machine cracked by Alan Turing
• Source of wealth bearing good returns, a mystery
• It's hard to figure out
• "Sadeness (Part I)" electronic band
• Puzzle that's a stumper
• Hard puzzle to figure out
• Brain-twister
• It's truly puzzling
• Puzzle that's new in processing image
• Shown up, Paul's clothes embarrassing ultimately, a poser