Jupiter is a system with a machine from 1975 that the East German Stasi and military used to change letters into numbers to send secret messages.

How did Jupiter originate?

Jupiter came after the older Juno system. The Juno system had two separate machines: the T-304 Leguan and the T-305. These machines were used by the HVA, the foreign intelligence service of the GDR.

With Jupiter, the functions of these two machines were combined into one device. This made the work easier and faster. The later version, the T-307/3, received a memory, a connection for a printer, and a screen. The method was officially recorded in 1975 in a Stasi regulation.

What is Jupiter?

Jupiter works in two steps to make a message secret. In the first step, the machine changes letters into numbers using the JUPITER substitution table. Letters that appear frequently get one number, and other letters get two numbers. Numbers in the text are always written three times in a row. For words that the intelligence service used often, there were special codes of five numbers. With Jupiter, this letter substitution happened automatically, whereas before it was done by hand.

In the second step, the same machine makes the message extra secure. The machine adds random numbers to the numbers from the first step. This is called the Ziffernadditionsverfahren (also known as Verfahren 001). There is a special calculation rule: if the sum is ten or more, you only write down the last digit. For example, 6+7 becomes 3. The result is a list of numbers sent in groups of five. The person who receives the message does the same thing but in reverse to read the text again.

The Jupiter function

In GC Wizard you can find this function in the folder Encryption and Codes → Jupiter

How does the function work?

The Jupiter function encrypts and decrypts texts according to the Jupiter method.