Eine verschlüsselte Postkarte, Alan Turing, die Enigma und eine Brief-Verschlusstechnik sind die heutigen Themen. Die Hinweise darauf kamen von meinen Lesern.

The keywords used for the Double Columnar Transposition (DCT) should have relatively prime lengths. But why?

A century ago, cryptologist André Langie reported about a really difficult dictionary cryptogram he had allegedly solved? Was it a strike of genius? Or was it a lie? Here is a similar challenge.

In his ground-breaking book “The Codebreakers”, David Kahn mentions a manual encryption method from 1929 he calls “ingenious”. However, neither Kahn’s book nor any other literature source I know gives a description of this method.

In 1931 US shoe manufacturer Hood published a series of advertisements containing encrypted messages in a boy scout magazine. Can you solve them?

Encrypted newspaper advertisements were very popular in the 19th century. The ones I am going to introduce today are much younger. They were published in the 1980s.

Edgar Allan Poe once asked the readers of a magazine to send him encrypted messages. He could break all of them, except two.

Codebreaker genius William Friedman needed 15 minutes to break this cryptogram. His wife Elizebeth, an outstanding cryptanalyst in her own right, needed 17 minutes. How fast can you solve it?

In WW2 German spy Wulf Schmidt used a simple encryption method based on a crossword puzzle.

In the British National Archives I found a small codebook from World War I. Apparently, it contains a German code that was reverse-engineered by British codebreakers. Many details about the origin of this codebook are unclear.