Simplified Lorenz Cipher Toolkit

To make best use of this page, please refer to the Codes & Ciphers resources available
from Bletchley Park National Codes Centre. You can view these resources here.

NOTE: You can use standard copy and paste functions to move sequences of letters between the sections of this page.

Simplified Cipher Wheels
The original Lorenz Cipher Machine had twelve wheels, but this version only has two.
The green area on each wheel indicates the current wheel position and cipher letter.
You can use the two buttons on the left to set the initial positions of the two wheels.

K PositionK Letter S PositionS Letter


Method for "Adding" Letters
The Lorenz Cipher method requires cipher letters to be "added" to the letters in the plaintext message.
This is done by firstly converting both letters to a five-digit binary number, then combining them using a XOR operation.
You could just use the teleprinter addition table which can be found here.
Finally, you could just use the form below. Enter the two letters you want to add, then press the "add" button.

First letter Second letter              Result


Enciphering/Deciphering Method

With the Lorenz Cipher, deciphering and enciphering use the same method.
The process below is described in terms of enciphering a plaintext message, but works identically for deciphering.

Once a starting position is chosen for each wheel, the message is enciphered as follows:
  (i) Add the the cipher letter on the K-wheel to the letter from the plaintext message.
  (ii) Add the cipher letter on the S-wheel to the resulting letter to get the first enciphered letter.
  (ii) Rotate both wheels one place and move on to the next letter to be enciphered.
This carries on until all letters have been enciphered.

Encipher the word "HELLO" with the starting position K=7, S=2.
K=7 S=2 K-Letter=G S-Letter=A H+G=C C+A=F The H in HELLO enciphers to F
K=8 S=3 K-Letter=H S-Letter=B E+H=Y Y+B=N The E in HELLO enciphers to N
K=9 S=4 K-Letter=I S-Letter=B L+I=H H+B=F The first L in HELLO enciphers to F
K=10 S=1 K-Letter=J S-Letter=A L+J=B B+A=G The second L in HELLO enciphers to G
K=11 S=2 K-Letter=K S-Letter=A O+K=Q Q+A=H The O in HELLO enciphers to H
So starting at K=7 S=2, the word "HELLO" enciphers to "FNFGH".


Automatic Enciphering and Deciphering Facility
We are interested in attempting to encipher and decipher Simplified Lorenz Cipher messages.
For this reason a facility for enciphering and deciphering messages quickly is provided here.
The same facility is used for both enciphering and deciphering, because the method is the same.
Simply put in the starting positions of the K and S wheels and the plaintext or ciphertext message, then click "Encipher/Decipher".

K-wheel start position =       S-wheel start position =
Plaintext message / ciphertext message (max 60 characters)
Enciphered message / deciphered message
NOTE: You can only use "A" to "Z" and "3", "4", "8", "9", "+" or "/". Spaces are invariably represented by "99".


Tools To Help Break The Simplified Lorenz Cipher
In the pupil notes you will find Exercise 6 which relates to breaking this simplified Lorenz cipher.
This section is based around a coded message Z.
You could of course try to decipher this message with each possible setting of K and S.
There would be 56 combinations (144) but in a real Lorenz Cipher machine there would be several billion.

Producing a ΔZ sequence
The process for breaking the code described in Exercise 6 requires the production of a "ΔZ sequence".
ΔZ is found by "adding" each pair of values in Z (i.e. first and second, second and third and so on).
You can create your own ΔZ sequences from a message Z using the form below.

Z =
ΔZ =

Producing a ΔK sequence
We also need to produce a "ΔK sequence".
ΔK is produced from K in the same way as ΔZ is produced from Z.
The K sequence must be the same length as the Z sequence, and is formed by cycling through the K-wheel letters.
e.g. If the K-wheel start-position is 7 i.e. letter "G",
You can create your own K and ΔK sequences using the form below. Just enter the start position and number of letters.

K-wheel start position =       Number of letters in Z/K sequences =      
K =
ΔK =

Adding the ΔZ and ΔK sequences and counting the "/" symbols.
To help us break the code, we also need to add the ΔZ to the ΔK sequence for each of the 14 K-wheel start positions.
We then need to count up the number of times the character "/" appears in these ΔZ+ΔK sequences.
Theoretically, the ΔZ+ΔK sequence where "/" appears the most often corresponds to the correct K-wheel start position.
You might like to try the main example, Z = UDZDMR+JMSDC+TXUVQMYEDE8LWOKUD3TMK+G4UDC3NXWKOBYEFURWH
You can create the 14 ΔZ+ΔK sequences using the form below.
You will only need to enter the Z sequence (the ciphertext message) and press the "Find ΔZ+ΔK" button.
The right-hand column shows the number of "/" characters in each sequence.

Z =
No. of "/"


Produced by A.J.Reynolds March 2005