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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.
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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.
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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].
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English: Reserve hand-procedure.
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The following documents are needed for the encrypting or decrypting RHV messages [2]:
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Related documents on this website
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- Reservehandverfahren Allgemein (wanted)
M. Dv. Nr. 929/1. Berlin, 1940.
- Schlüsselheft Nr. 16
Zu M. Dv. Nr. 929/1. Berlin, 1942. 1
➤ Printable version
- Schlüsselheft Nr. 18
Zu M. Dv. Nr. 929/1. Berlin, 1942. 1
➤ Printable version
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Document kindly privided by Glen Miranker and scanned by Crypto Museum.
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© Crypto Museum. Created: Thursday 02 July 2020. Last changed: Sunday, 29 May 2022 - 13:24 CET.
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