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OTP   DDR and USSR
East-Germany and Soviet Union

During the Cold War, for former DDR (East-Germany) as well as the former USSR (Soviet Union), used One-Time Pad (OTP) cipher systems for secret communication between agents, operating in a foreign country, and their control in Berlin or Moscow. For this purpuse they used small OTP booklets that were smuggled into the target country inside a concealment or via diplomatic mail.
 
The image on the right shows a typical OTP booklet as it was used by agents of the former Soviet Union (USSR) and East-Germany (DDR) during the 1960s. It was used by an agent for decoding encrypted instructions that were sent via Numbers Stations on the short wave radio bands as well as for sending messages by means of a spy radio transmitter (often a Russian one).

The booklet consists of a stack of 50 very thin small pages, each with a 60 five-digit groups, organised as 10 rows by 6 columns. The pages are folded, perforated and then sewed together.
  
Courtesy AIVD Netherlands [1]

Each time a page is needed, it has to be torn at the perforated edge. For each new message, a fresh OTP sheet was used. If the message was longer than one page, multiple OTP pages were used. If it was shorter, the rest of the page was discared. After use, the page was destroyed.
 
The pages of the booklet are sewed together and then glued inside an orange carton cover that was then folded and closed with a wax seal in order to make it tamper-evident. In the booklet shown here, the page on top of the stack is numbered 19, which means that the agent had already used it in the past to send or receive at least 18 secret messages before he was caught.

The books were printed on very thin paper. This made it possible to make them thinner and smaller, but also had the advantage of making it easier to destroy (burn or eat) them after use.
  
Courtesy AIVD Netherlands [1]

OTPs like this, were commonly used by secret agents for sending coded messages to control, using a Russian spy radio set like the R-353. Most agents however, did not have a spy radio transmitter, but used the OTP for decoding the secret instructions that were sent by control via the mysterious Numbers Stations on the short wave radio bands. The OTP booklet shown here is from the internal collection of the Dutch Intelligence Agency AIVD, and was found in the house of a Dutch man who was working as an agent for the East-German intelligence service, the Stasi.
 
Closed OTP booklet Seal broken Small booklet OTP booklet used by the DDR during the Cold War Holding the OTP booklet in the palm of a hand Close-up of a single page Tearing off a page OTP with random 5-number groups

 
Concealment
The OTP shown above, dates back to the days of the 1960s, when the Cold War was at its height. Eastern Block spies, and in particular spies from East-Germany (DDR), often used OTPs for their messages, as it was absolutely safe and could not be broken by the western intelligence agencies.
 
The major problem with OTPs however, is their distribution. A unique set of OTP booklets needs to be issued and distributed to each individual spy or agent abroad. As the OTP was destroyed immediately after use, sufficient and timely supply of new OTPs had to be guaranteed.

OTPs were often smuggled into the country by using concealments like the one shown in the image on the right. In this case a common travel kit is cleverly converted into a concealment device by the East-German secret service.

 More information
  
Courtesy AIVD Netherlands [1]

 
Capture
OTP booklets, such as the one shown above, have been captured during the Cold War by Western intelligence agencies on a number of occassions. One documented example is the capture of a Dutch man, who acted as an East-German agent in The Netherlands, in 1969. When he was finally exposed, the Dutch intelligence agency BVD (now: AIVD) found a partly used OTP booklet in his home, along with a fully operational R-353 spy radio set, a burst encoder and cassettes [1].

Complete R-353 with burst encoder and OTP cipher booklet

 
References
  1. AIVD, One-Time Pad and OTP concealment
    Dutch General Intelligence and Security Service. October 2010.

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Crypto Museum. Created: Friday 28 August 2015. Last changed: Friday, 30 December 2016 - 09:25 CET.
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