## Was meine Leser mir geschrieben haben

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

## Two DCT challenges and a question about them

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

## A dictionary code challenge

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.

## Jack Levine’s ingenious encryption method: How does it work?

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.

## Four cryptograms from a 1930s treasure hunt

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

## The Darknet of the Eighties

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.

## How Edgar Allan Poe broke about 100 ciphertexts

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

## Can you solve this cryptogram as fast as two of the best codebreakers in history?

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?

## A crossword encryption used by World War II spy Wulf Schmidt

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

## A reverse-engineered codebook from World War I

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.