Participants of the International Students’ Olympiad in Cryptography have to solve a number of tough crypto challenges. Here are a few of the nicest ones. Can you solve them?

A German memorial coin minted in 2011 bears a hidden code. Maybe my readers can help me to find out more about it.

Earlier this year I blogged about Printer Identification Codes, which are one of the IT world’s best-kept secrets. As it seems, a US secret service has now used this technology to track down a whistleblower.

US mathematics professor Craig Bauer has published a great book about unsolved cryptograms. Most of these crypto mysteries have been covered on this blog before.

The Handycipher is an encryption algorithm that doesn’t require a computer program or a machine. But is it secure?