S
Q
U
A
N
D
E
R
Then you fill up the remaining spaces with the rest of the.alphabet in order, leaving out the ones you’ve already got.’
‘You, can’t put twenty-six letters into twenty-five spaces,’ objected Glaisher.
‘No; so you pretend you’re an ancient Roman or’ a medieval monk and treat I and J as one letter. So you get this.’
S
Q
U
A
N
D
E
R
B
C
F
G
H
IJ
K
L
M
O
P
T
V
W
X
Y
Z
Now, let’s take a message What shall me say? “All is known, fly at once”—that classic hardy perennial. We write it down all of a piece and break it into groups of two letters, reading from left to right. It won’t do to have two of the same letters coming together, so where that happens we shove-in Q or Z or something which won’t confuse the reader. So now our message runs AL QL IS KN O W NF LYAT ON CE.’
‘Suppose there was an odd letter at the end?’
‘Well, then we’d add on another Q or Z or something to square it up. Now, we take our first group, AL We see that they come at the corners of a rectangle in which the other corners are SP. So we put down SP for the first two letters of the coded message. In the same way QL becomes SM and ISbecomes FA.’
‘Ah!’ cried Glaisher, ‘but here’s KN. They, both come on the same vertical line. What happens, then?’
‘You take the letter next below each — TC. Next comes OW, which you can do for yourself by taking the corners of the square.’
‘MX?’
‘MX it is. Go on.’
‘SK,’ said Glaisher, happily taking diagonals from corner to corner, PV, NP, UT
‘No, TU. If your first diagonal went from bottom to top, you must take it the same way again. ON=TU, NO would be UT.’
‘Of course, of course. TU. Hullo!’’ ‘What’s the matter?’
‘CE come on the same horizontal line.’
‘In that case you take the next letter to the right of each.’
‘But there isn’t a letter to the right of C.’
‘Then start again at the begining of the. Line’
This confused the Superintendent for a moment, but he finally produced DR
‘That’s right. So your coded message stands now: SP SM FA TC MX SK PV NP TU DR. To make it look prettier and not give the method away, you can break it up into any lengths you like. For instance. SPSM FAT CMXS KPV NPTUDR. Or you can embellish it with punctuation at hapazard. S.P. SMFA. TCMXS, KPVN, PT! UDR It doesn’t matter. The man who gets it will ignore all that. He will simply break it up into pairs of letters again and read it with the help of the code diagram. Taking the diagonals as before, and the next letter above, where they come on the same vertical line, and the next to the left where they come on the same horizontal.’
The two policemen pored over the diagram. Then Umpelty said:
‘I see, my lord. — It’s very ingenious. You can’t guess it by way of the most frequent letter, because you get a different letter for it each time, according as it’s grouped to the next letter. And you can’t guess individual words, because you don’t know where the words begin and end. Is it at all possible to decode it without the key-’word?’
‘Oh dear, yes,’ said Wimsey. ‘Any code ever coded can be decoded with pains and patience — except possibly some of the book codes. I know a man who spent years doing nothing else. The code diagram got so bitten into him that when he caught: measles he came out in checks instead of spots.’
‘Then he could decode this,’ said Glaisher, eagerly.
‘On his head. We’ll send him a copy if you like. I don’t know where he is, but I know those that do. Shall I bung it off? It would save us a lot of time.’
‘I wish you would, my lord.’
Wimsey took a copy of the letter, pushed it into an envelope and enclosed a brief note.
‘DEAR CLUMPS, — Here’s a cipher message. Probably Playfair, but old Bungo will know. Can you push it off to him and say I’d ‘ be grateful for a construe? Said to hail from Central Europe, but ten to one it’s in English. How goes?