The Cardboard Box Cipher

Question

Here's a one-step monoalphabetic substitution cipher that I originally posted on CodeAWeek. (Link in my profile.) The key to solving it lies within the following poem:

A clerk gave me a cardboard box
that now I give to you
It once held t-shirts, jeans, and socks
It now holds one left shoe
Take out the shoe and put it on
then head to liquor store
Now drink the whiskey till it’s gone
and then drink thirteen more
Pack my box with liquor jugs,
five dozen — all in all
Checkout with clerks and give them hugs
and then go have a ball
Don’t wreck your car, though you are wrecked
and don’t heed every sign
Dead ends, some lead to misdirect,
save line and half a line

And here is the ciphertext:

SOMRF XCIAJ QELYQ DWFHU GQVMJ SOMTP NZKQB

Since the cipher is mono-alphabetic, some people might be able to crack it without relying on the poem. But to win this, you must decode the message AND explain how the poem unlocks it.

Answer 1

The message deciphers to

THEQU ICKBR OWNFO XJUMP SOVER THELA ZYDOG

or, grouping into words,

The quick brown fox jumps over the lazy dog

Explanation:

The poem includes the phrase "Pack my box with liquor jugs, five dozen", which is (a variation of) a sentence which is famous for containing every letter in the English alphabet. This makes it a likely candidate to be the cipher key.

Writing this with each occurrence of a letter that has already appeared earlier in the phrase removed (i.e. keeping only the first instance of any repeated letters) above the alphabet in the usual order gives

PACKMYBOXWITHLQURJGSFVEDZN

above

ABCDEFGHIJKLMNOPQRSTUVWXYZ

and substituting for each letter in the cipher the one which appears below it in this double alphabet gives the solution above

which is another phrase famous for containing every letter of the English alphabet.