Decipher a Code Stick

Question

Introduction

You're an American spy during the heat of the Cold War and you've managed to intercept a Russian message. Immediately you recognise it as a code stick cipher and wrap it around a pencil. Looking at the paper on the pencil, you don't see anything. Then you try a bigger pencil, and you see it.

Challenge

You have to write a program that deciphers a code stick. As this is code golf, the shortest program wins.

You may use any English dictionaries for looking up words. Some examples of dictionaries include:

• Querying a text file of words
• Using an inbuilt OS dictionary
• Querying an online dictionary (screen scraping etc.)
• Using an external lib

All words MUST be valid English words

Your pencils

Each of your pencils has four equally sized faces and are infinitely long. You have five differently sized pencils:

Pencil 1: Shows 1 character on each face
Pencil 2: Shows 2 characters on each face
Pencil 3: Shows 4 characters on each face
Pencil 4: Shows 6 characters on each face
Pencil 5: Shows 8 characters on each face

All ciphers can be deciphered by placing the start of the paper at the top of the pencil and wrapping it down.

Examples

The following is an example of a cipher:

Hepoge slljghadso bvvbgh

This can be deciphered by wrapping it around Pencil 2:

Side 1 | Side 2 | Side 3 | Side 4
-------+--------+--------+-------
He     | po     | ge     |  s
ll     | jg     | ha     | ds
o      | bv     | vb     | gh

So now you have four combinations:

Hello , pojgbv, gehavb,  sdsgh

You can now perform a dictionary lookup and see that Hello is the only valid word. Therefore, Hello is the cracked cipher.

Note: Deciphered codes may have spaces in. Example: Hello World

Test cases

Ciphers can be inputted in any way apart from being hardcoded. The following are a few test cases. You will not be given the pencil size.

boasonespetrabbittonespongomezesray long
lsbvmii derfghthstthasinlomnrtk fg dndthugssawerpoloasefnxafqeormnaqwge padhndi mbavwgam
lipois lisptloopoolsisp lortfippinglthe asse rtedgoodcodeis the best  of enlymoolfangthe  leamingsoulsgodsingering
antidisebd sldkfdw sld sja dmddystablishjzkapxmjhavzlx dld slzbfmentariabahdjdlljagzlxbxlffnd ldnism is hdbsh spjalcpdhstd flcnda very cbd skd alsbfo kfvwfd xlconvolutehs ska ckw dlc fjzlxbckxd word  hs sla k dk skdnlcjcu dk

Any more test cases would be appreciated

Answers to the test cases

1: astronomy
2: i think therefore i am
3: is lisp the code of the gods
4: antidisestablishmentarianism is a very convoluted word

Script to generate code stick ciphers:

import string, random, math

word = input('Word:\t')
n = int(input('Pencil:\t'))
pencil = int(-((4*(17*n-77))/((n**4)-(19*n**3)+(136*n**2)-(444*n)+566)))

alpha = string.ascii_lowercase+' '
cipher = ''

side = random.randint(1, 4)
sides =['','','','']

for j in range(len(sides)):
    if j+1 == side:
        sides[j] = word
        if len(word)%pencil != 0:
            sides[j] += ' '*(len(word)%pencil)
    else:
        for k in range(math.ceil(len(word)+(len(word)%pencil))):
              sides[j]+=random.choice(alpha)

for l in range(0, math.ceil(len(word)/pencil)*pencil, pencil):
    for m in sides:
        cipher += m[l:l+pencil]

print('Cipher:\t'+cipher)
print('Side:\t'+str(side))

Answer 1

Python - 219 178 172 175

First crack at it. I'm sure there's room for improvement.

edit1: After suggestions, and copying words file to local file named 'w'
edit2: Fixed a bug where it wasn't using the right number of letters per side. Added 3 chars :(

r=range 
s=raw_input()
print[a for a in(''.join(s[m:m+n]for m in r(o*n,len(s),4*n))for o in r(4)for n in(1,2,4,6,8))if not set(a.lower().split())-set(map(str.strip,open('w')))]

Answer 2

Mathematica 270 230 251

---

This now requires that all parsed words be found in a dictionary.

f@q_:=
Module[{c=Characters@q,wd,u=DictionaryLookup},
j@d_:=Union[u@d,u[ToLowerCase@d],WordData@d];
Flatten@Select[Flatten[Table[
StringSplit[""<>Flatten@#]&/@Transpose@ArrayReshape[c,{Round[Length@c/(4 m)],4,m},""],{m,{1,2,4,6,8}}],1],!MemberQ[j/@#,{}]&]]

Test Cases

f["boasonespetrabbittonespongomezesray long"]
f["Hepoge slljghadso bvvbgh"]
f["lsbvmii derfghthstthasinlomnrtk fg dndthugssawerpoloasefnxafqeormnaqwge padhndi mbavwgam"]

{"astronomy"}
{"Hello"}
{"i", "think", "therefore", "i", "am"}