The Cipher Event
by Tony Sale | Back to Index |

Tony Sale's
Codes and Ciphers

The Colossus Rebuild Project in
the National Museum of Computing

The Cipher Event.

To celebrate the completion of the Colossus Mk 2 Rebuild

What is it?

To transmit, by radio, by teleprinter, from the Heinz Nixdorf Computer Museum in Paderborn in Germany, a series of secret messages enciphered on a WW II Lorenz SZ42 cipher machine.

To issue a world-wide challange to anyone to break the cipher settings and decipher these messages before the Rebuild of WW II Colossus Mk 2 in Bletchley Park does it.

Breaking the messages.

Starting with an easy one, wheel patterns for all 12 wheels given and start positions for the M and Psi wheels revealed. Just find Chi wheel starts and decipher.

More difficult, all wheel patterns given but no wheel starts.

Yet more difficult, no Chi wheel patterns or starts but other wheel patterns available but no starts.

The killer, no patterns or starts for any wheels.

The timetable.

September 2007

Refurbish the Bletchley Park Lorenz SZ42 cipher machine

October 2007

Ship the SZ42 to Hienz Nixdorf Museum in Paderborn If sending the SZ42 is a problem, then a proven software simulator will be sent.

Do test radio transmissions of unciphered teleprinter text.

November 2007

15th and 16th, the transmission of enciphered texts.

The radio transmissions.

These will be exactly as transmitted in WW II. Multi-tone modulation on the transmitted RF carrier. Two sets of tones were used, one representing a mark or 1 in the Baudot code, the other representing a space or 0 in the Baudot code. Three tones were used in each one and these tones were chosen to be not harmonically related. Their frequencies were 540 cps + n * 180 cps. Actual frequencies, Mark 900,1620,2340 Space 540,1260,1980.

So what is required is a set of audio tone generators at the transmitting end and a set of selective tone filters at the receiving end.

The radio transmitter system requires the teleprinter signal to be in serial form. The Lorenz SZ42 cipher machine accepts the serial form, converts it internally to 5 bit parallel form, enciphers each character and then converts the resultant cipher character back to serial form.

At the receiving end the audio output from the radio receiver goes to the bank of audio filters which detect whether the tones represent a mark or a space. This serial form of the Baudot code can then directly drive a suitably fast teleprinter, but was more usually recorded on a long strip of paper tape by an undulator ink pen recorder.

As used by the Germans, the serial form went through the Lorenz SZ42 cipher machine at the receiving end before the deciphered text was printed on a teleprinter.

Both transmitting and receiving SZ42s had to be configured exactly the same, same wheel patterns on all 12 wheels and same wheel start positions.

The interceptor has to find both patterns and wheel starts in order to decipher an intercepted message.

The format for serial Baudot code teletype signals.

The elements of the Baudot code are Marks and Spaces. Marks are a "1" or a punched hole on paper tape, Spaces are "0" or no punched hole on paper tape. A Baudot code word in serial form consists of a start Space followed by the five elements of the code being sent. For instance the code letter "A" is sent in serial form as Space, Mark, Mark,Space,Space,Space.

A teleprinter link sits in the Mark state if no Baudot code words are being sent. Then when the start Space occurs it activates the teleprinter mechanism and the next five elements are interpretted as the Baudot code word of five bits. After the fifth element the telprinter link reverts to the Mark state.

sample transmission of the alphabet

An emulation of the SZ42

Tony Sale, Leader, the Colossus Rebuild Project and Trustee/Director of the National Museum of Computing


This page was originally created by the late Tony Sale
the original curator of the Bletchley Park Museum