The history of encryption is a tale of broken secrets. But some mysteries remain unraveled. Among the thousands of broken codes and ciphers solved by cryptologists from the NSA and the KGB to amateurs at home, there are the few elusive codes that no one has ever managed to crack.
What makes these ciphers even more intriguing are the people who supposedly wrote them: an estranged lover; a serial killer who sent encrypted letters in a kind of twisted mind game; an esoteric 15th century alchemist for reasons still unknown today. Some of the codes turned up in the pockets of dead men: some unidentified to this day, others who were murdered by strangers for no discernible reason why.
Some may even be hoaxes. But even figuring out which ciphers are real and which are not can be nearly insurmountable. And even if we can spot the authentic codes amidst the hoaxes, some of these rare and challenging codes may still be impossible to solve, in our lifetimes at least. We've asked Kevin Knight – the University of Southern California computer scientist who recently helped crack the 250-year-old Copiale cipher – to walk us through seven of the most confounding codes and give us an idea of what makes these things so tough to break.
