The lines ...
3 5 7 9 N O P Q R S T U V W X Y Z
2 4 6 8 . A B C D E F G H I J K L M
are the characters used on an early typewriter designed by Christopher Latham Sholes. He went on to invent the first typerwriter with a QWERTY keyboard layout, the same layout used on modern day computer keyboards.
That clue leads to ...
... your own computer keyboard being the codebook.
Using your keyboard as the codebook, you can follow the rules of the Playfair cipher to decipher the code. The grid would look like this:
QWERTYUIOP
ASDFGHJKL;
ZXCVBNM,./
The deciphered text is
T H E X A S E A N D F R E X D O M A N D B E A U T Y W I T H W H I C H T H I S M A C H I N E W O R K S I S T R U L Y W O N D E R F U L E V E R Y T H I N G N O W S E E M S T O M E A S P E R F E C T A S I T C A N B E M A D E A N D I F E X L N O I N S P I R A T I O N T O A ; T E R A N Y T H I N G F U R T H E R
or
THE EASE AND FREEDOM AND BEAUTY WITH WHICH THIS MACHINE WORKS IS TRULY WONDERFUL. EVERYTHING NOW SEEMS TO ME AS PERFECT AS IT CAN BE MADE AND I FEEL NO INSPIRATION TO ALTER ANYTHING FURTHER.
TheAs with the Playfair cipher is,
similar to get the Playfair cipherfinal deciphered text from the raw decipher, exceptreplace X's with the grid is (most of)previous letter. I also had to perform an extra shift for the QWERTY keyboard:
QWERTYUIOP ASDFGHJKL; ZXCVBNM,./To get the final deciphered text from the raw decipher, replace X's with the previous letter. I also had to perform an extra shift for the 'L' in 'ALTER', as it was deciphered as ';'.'L' in 'ALTER', as it was deciphered as ';'.
The plaintext is
a quoteExcerpts from an 1870 letter by Christopher Latham Sholes about his new typerwriter. It was some of the newly-invented typewriterfirst text ever written on the QWERTY typerwriter.
