There's no need to answer my question above, but I'll leave it for others' benefit. I assumed I need to conserver spaces, punctuation and letter case. I dropped the '-marks.
Here, then, is my only entry in this contest. Now actually to be found in the correct place.
Pekka's railwpsa Cipher
railwpsa spsigli ngnaragtnira ,aiavilr rtnhopsaby Iacmsptu.w s liht ate.nr,a
re Tsr reuesrarhh oanec dlil audg wohayiepspvsilta pwelsespai,roisTeu plnhlin
tdm,hr e oowangtyye eecnhc rf h,t,ocaiw eiuoe e nl drpln fsapddias lti endul
pyrllva qar oti ssrodgh,e icilytdpesoyesscdrlsoea.vrsip
The railwpsa method consist of writing the text in a spiral starting from the center, padding the text so it makes a square with an odd side length, and then reading it in diagonals, starting from upper left. The details are as follows.
Where the text begins is the center of the spiral. First I go right from there and then continue wrap the text around clockwise. When it runs out, I pad the spiral with the word 'spiral' repeated and run together until I get to the the upper right corner. For this text, this makes for a 17 x 17 square with the initial T in the center.
Next I read the text in consecutive diagonals, starting from the upper left corner. The diagonals start from the first yet unread letter and go down and left. Thus the coordinates of the first few diagonals are as follows:
Just upper left corner: (1,1)
Next line of two chars: (2,1) to (1,2)
Next line of three chars: (3,1) to (1,3) (via (2,2))
and so on, until I finish in the bottom right like so
(17,15) to (15,17) and (17,16) to (16, 17) and lastly, (17, 17).
As a result of this, the initial letters of the plaintext is put right at the middle of the ciphertext. That is the capital 'T' in 'roisTeu' in the ciphertext here.
This gives the encrypted text, which I have broken into lines of 78 characters in a cheap attempt to confuse the cryptanalyst
.
Now to decrypt it. Counting the letters and other characters carefully, we find that the message consists of 289 characters, which implies it fits into a square of 17 x 17 spots. We start filling these from the upper left corner in the same order they were read originally. Thus I first put the initial 'r' into the top left corner. Then I write 'a' to the right of it and 'i' below. The third diagonal consists of the three letters 'lwp', and so it goes until I fill the square, writing the last letter in the bottom right corner.
Then it is a matter of just reading the text starting from the center square, going right once and then following the unread letters clockwise. It should be the original text to the letter, unless I made a mistake somewhere along the line. I did double-check by noting that many letters ended up exactly where they should have.
I hope you enjoyed puzzling this one out. The spiralspiralspiral filler was meant as a little hint, because it ended up as a part of the initial string railwpsa.