Comments from Matthew Newell and Jim Gillogly
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Comments from Matthew Newell
most urgent stop
all members of glider team killed stop
in contact with norsk hydro informant stop
red penguin frenzy stop
do not send followup team until I give coordinates
and time for safe landing zone end
VYTES YEDLU TERVL FNVUH DWARD LCFFB SDEWN PXKIC
mostu rgent stopa llmem berso fglid ertea mkilx
FTREO LKALZ YLSLT OBKEV LYARM KRBOD NALDY PLAET
ledst opinc ontac twith norsk hydro infor mants
OLQAD FHSFZ WNAID SMURU OLHRY LLOTW FYLDI CVLUS
topre dpeng uinfr enzys topdo notse ndfol xlowu
VSSFZ YLUNF FXLKT GBCDO BFALE WRPFY WLHUL DARLI
pteam until igive coxor dinat esand timef orsaf
TFLAB FFZCY FUUFB GXXXX
eland ingzo neend x
Encryption square as follows:
u s t e w
y r o d b
n a l f i
m p v h k
z q c g x
Can see neither rhyme nor reason to it, so I would hazard a guess that
(as he is working under duress) that he used a random square in order
to fool gerry into thinking that this is always the case (protecting his
colleagues' future messages).
As no four-letter sequence was repeated, I guessed all stops were split -S to P-, so identified repeated two-letter sequences. OL, AR, and LD all appeared three times, and as I presumed such a long message would have at least four or five sentences, I concentrated on these.
- recognition/compromise code
I then looked at the gaps between the above three sequences to see if any gave correct room for the code (both 16 letters) and the final P of the first stop and the initial S of the last stop, i.e., 18 spaces. OL fit the bill.
If code had been recognition, the second pair and the sixth pair would have been reversals of each other (EW - WE) unless the coding letters where particulary unluckily placed (which they were).
I assumed that thus we had received the compromise code (lucky guess in end).
- start of reconstruction of code square
Then, using the 18 coded letters, I was able to recontruct a three-by-three square (less one). Translating all the code that used these letters left large gaps.
- With guesswork, I was able to fill in the rest using completion of the work I had partially translated and the spatial relationship of letters on the code square that I was able to deduce from known code.
bixente (Matthew Newell)
Comments from Jim Gillogly
This solution is perfectly correct. He did not find the keyword in the encryption square, which points up an interesting feature of the Playfair: The rows and the
columns may be rotated either up/down or left/right without changing the encryption. In this case, rotating his square two columns to the right would show the word FINAL on one row, giving the square enough extra coherence to allow him to notice that rotating it two rows down would put the rest of the spiral keyword in order. Keyword recovery is important in cryptanalysis, since a clear understanding of the enemy's keying strategy will speed the break into tomorrow's traffic.
He conjectured that the agent had used a random square. The Germans did use random Playfair squares, but not (so far as I know) for field agents with memorized cipher systems.
The analysis steps were done flawlessly (which is to say, the way I intended them to be done): Identify STOP and test for the confirmation or duress codes, making conjectures and testing them. Well done!
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