Re: Term of Art

James P. Anderson wrote:

> In the paperback book "Code Breakers" by F.H Hinsley and Alan Stripp 
> (a collection of remininces of people who were at BP during WW II), 
> there is in a section on German Manual Ciphers a reference to a 
> transposition "cage". The quote (p238, bottom of page) is
> "...RHV involved transposing the clear text through a "cage" and then 
> applying vertical bigram substitution to the transposed text on four 
> different substitution tables..." The substitution is described 
> elsewhere.
>
Ha! Let me guess.... you're part of the M4 project trying to break that 
elusive message and noticed the comment from Ralph Erskine and Frode 
Weierud stating that the messages are probably Enigma but could possibly 
be RHV. So you went looking up RHV (as I did) and came up with Hinsley 
and Stripp (as I did). Nothing in wikipedia I notice - "Matt Crypto" is 
slipping!

> I have never encountered the term "cage" in connection with a 
> transposition step. Can you tell me what they are describing? The only 
> "cage" I have ever heard of is the sliding bar drum in Hagelin machines.
>
I've seen this nomenclature before somewhere, but I can't remember 
where. Basically, IIRC, the "cage" is a position-scrambling lookup 
table. Different 'cages' are probably specified for each day (or pair of 
days, this being Kriegsmarine).

For instance: maybe the "cage" for the day is 8x1 long as follows:

1  2  3  4  5  6  7  8
5  7  4  3  1  8  2  6

This "cage" is reciprocal, but it doesn't have to be. A lot of German 
cipher stuff in WWII does seem to be recipriocal however, and it's quite 
possible RHV was.

So you write your message in groups of 8. Take the message "nothing 
important happening today".

The first group of 8 is "N O T H I N G I" and we swap the 1st and 5th, 
2nd and 7th according to the cage to give "I G H T N I O N".



RHV *is* probably documented properly somewhere, but without the bigram 
tables surviving and with just one message to attack with no cribs, it 
would be probably as hard to crack as the existing M4 enigma attack!

> TIA,
>
> Jim Anderson

Steve