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RHV
Manual backup procedure

Reservehandverfahren, 1 commonly abbreviated to R.H.V. or RHV, was a hand-cipher used during World War II by the German Kriegsmarine (Navy) as a backup system when no working Enigma cipher machine was available [1]. The cipher involves two stages: a transposition, followed by a bigram substitution. It was first solved by the British codebreakers of Bletchley Park in June 1941.

In the first stage, the plaintext is written out in a so-called cage or box, which was merely a shape on a piece of paper. Pairs of letters where then substituted by means of a set of bigram tables. A detailed description of this procedure can be found on the website of Michael Hörenberg [2].

An RHV-encoded message looks exactly like an Enigma message, and the procedure for creating one, is just as complex as creating an Enigma-encoded message. The RHV is far less secure, however. The image on the right shows a rare copy of THV Schlüsselheft number 16 of 1942.
  
RHV Schlüsselheft 16 with other code material

It is part of Marine Dienstvorschrift 929/1 (M. Dv. Nr. 929/1), of which the general procedure is layed out in Reservehandverfahren Algemein [A]. A series of cipher books (Schlüsselhefte) to be used alongside, were issued at several moments in time, for example in 1940, 1942 and 1944.

The RHV cipher was first solved at Bletchley Park (BP) – Britain's wartime code breaking centre – in June 1941, aided by documents retrieved from German U-boat U-110 that had been captured the previous month. In the following three years it was solved by means of cryptanalysis, with about 1400 signals read in total [3]. The decrypts were of limited importance from an intelligence point of view, but were commonly used to find cribs for solving Naval Enigma. The section at Bletchley Park responsible for the RHV decrypts, was headed by British historian Sir John H. Plumb [4].

  1. English: Reserve hand-procedure.

RHV Schlüsselheft Nr. 16, 1942 ID and additional notes at the bottom left Contents of Schlüsselheft Nr. 16 (1942) Table 2 Start of a table Rear page Schlüssel M Allgemein, RHV Heft 16 and Bigram tables 'Quelle' RHV Schlüsselheft 16 with other code material
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RHV Schlüsselheft Nr. 16, 1942
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ID and additional notes at the bottom left
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Contents of Schlüsselheft Nr. 16 (1942)
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Table 2
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Start of a table
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Rear page
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Schlüssel M Allgemein, RHV Heft 16 and Bigram tables 'Quelle'
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RHV Schlüsselheft 16 with other code material

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Procedure
The following documents are needed for the encrypting or decrypting RHV messages [2]:

In English:

For a complete description of the RHV procedure, including working examples, please refer to the website of Michael Hörenberg (off-site) [2].

Related documents on this website
Der Schlüssel M - Verfahren M Allgemein (M.Dv.Nr. 32/1) Doppelbuchstabentauschtafeln für Kenngruppen - Quelle RHV Schlüsselheft Nr. 16 (featured on this page)
RHV
Documentation
  1. Reservehandverfahren Allgemein (wanted)
    M. Dv. Nr. 929/1. Berlin, 1940.

  2. Schlüsselheft Nr. 16
    Zu M. Dv. Nr. 929/1. Berlin, 1942.
References
  1. Der Schlüssel M - Verfahren M Allgemein
    M.Dv.Nr. 32/1. Berlin 1940. Page 4, index 2.
     English translation by Tony Sale

  2. Michael Hoerenberg, Reservehandverfahren (R.H.V.) M.Dv.Nr.929/1
    Retrieved July 2020.

  3. Wikipedia, Reservehandverfahren
    Retrieved July 2020.  German version

  4. Wikipedia, John H. Plumb
    Retrieved July 2020.
Further information
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© Crypto Museum. Created: Thursday 02 July 2020. Last changed: Monday, 06 July 2020 - 07:47 CET.
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