Here's the cipher text:
EUINRECSTNCIHRLYYEORYNDPUPTAIPTSNIONOUEIODMNTHIBTN THETESSREECWOEECLFOHNRPFRESRLIQDIHCYONOUEFCUOFLICS ERPDTHNLYVOPEOEKTSTLVOTBEYEHGEDRERTHEMASLPOQISUSHO WYTIPRRIWLYHMEINDPEOVNOTCIORAERTTBPLEATTHHNSEIETEE CEPCSJRRNENDIEUSTNOTUFCBTAUITRIHPTSRTLEESNEHELESIA UNTSEVTAEGUTTRANEEESTEDNTTGTNEKTHTODHAHERCTSAYHTEC KNHOASUETHOUMLITDERFFYTIWANHHSREOSSTTDPEVUOEHEAFBO LLEDNThere are exactly 355 characters there, and 5 is a divisor of 355 so write out the characters in blocks of 5:
E U I N R E C S T N C I H R L Y Y E O R Y N D P U P T A I P T S N I O N O U E I O D M N T H I B T N T H E T E S S R E E C W O E E C L F O H N R P F R E S R L I Q D I H C Y O N O U E F C U O F L I C S E R P D T H N L Y V O P E O E K T S T L V O T B E Y E H G E D R E R T H E M A S L P O Q I S U S H O W Y T I P R R I W L Y H M E I N D P E O V N O T C I O R A E R T T B P L E A T T H H N S E I E T E E C E P C S J R R N E N D I E U S T N O T U F C B T A U I T R I H P T S R T L E E S N E H E L E S I A U N T S E V T A E G U T T R A N E E E S T E D N T T G T N E K T H T O D H A H E R C T S A Y H T E C K N H O A S U E T H O U M L I T D E R F F Y T I W A N H H S R E O S S T T D P E V U O E H E A F B O L L E D NIf you stare that this you'll see some words appear. In fact, the third column reads (downwards) ISHEDANUMBEROFPRINCIPLESTHEMOSTIMPORTANTPRINCIPLES
TATEDTHATTHEMETHODOFE or ISHED A NUMBER OF PRINCIPLES THE MOST IMPORTANT PRINCIPLE STATED THAT THE METHOD OF E. So, switch the columns around into rows for easier readability.
EECYYPTNOHTSCCNEQYEFEHOKVYDHLSWRYNVIRLHICJNSUAIRSLUVUNTTKDRYKSOTFARTVEL UCIYNTSODIHSWLRSDOFLRNPTOEREPUYRHDNOTEHEERDTFUHTNENTTEEGTHCHNUUDYNETUAL ISHEDANUMBEROFPRINCIPLESTHEMOSTIMPORTANTPRINCIPLESTATEDTHATTHEMETHODOFE NTROPIIENTTEEOFLHOUCDYOTBGRAQHIWEETABTSECNEOBTTEHISERENNTHSEOTLRIHSPEBD RNLRUPOITNEEEHRICUOSTVELEETSIOPLIOCEPTEESEUTTRSEEAEGASTEOEACAHIFWSSEHONNow for a guess. Guess that that final E on line three is the start of the word ENCRYPTION and that the N on the next line is the next letter. Is it possible to find the complete word? Yes, by following a zig zag pattern. To make this easier rearrange the rows.
EECYYPTNOHTSCCNEQYEFEHOKVYDHLSWRYNVIRLHICJNSUAIRSLUVUNTTKDRYKSOTFARTVEL ISHEDANUMBEROFPRINCIPLESTHEMOSTIMPORTANTPRINCIPLESTATEDTHATTHEMETHODOFE NTROPIIENTTEEOFLHOUCDYOTBGRAQHIWEETABTSECNEOBTTEHISERENNTHSEOTLRIHSPEBD UCIYNTSODIHSWLRSDOFLRNPTOEREPUYRHDNOTEHEERDTFUHTNENTTEEGTHCHNUUDYNETUAL RNLRUPOITNEEEHRICUOSTVELEETSIOPLIOCEPTEESEUTTRSEEAEGASTEOEACAHIFWSSEHONThe bolded characters form the sentence NCRYPTION ITSELF SHOULD NOT BE REQUIRED TO BE SECRET BUT THE STRENGTH SHOULD INSTEAD and the non-bolded zig zag characters read UTIONISED THE WORLD OF CRYPTOGRAPHY WHEN AT THE END OF THE NINETEENTH CENTURY HE PUBL.
That just leaves two lines of cipher:
EECYYPTNOHTSCCNEQYEFEHOKVYDHLSWRYNVIRLHICJNSUAIRSLUVUNTTKDRYKSOTFARTVEL RNLRUPOITNEEEHRICUOSTVELEETSIOPLIOCEPTEESEUTTRSEEAEGASTEOEACAHIFWSSEHONAgain the zig zag pattern applies and it's possible to read RELY UP ON THE SECRECY OF THE KEY THIS PRINCIPLE IS JUST AS RELEVANT TODAY AS IT WAS THEN and ENCRYPTION TECHNIQUES EVOLVED SLOWLY OVER THE CENTURIES AUGUSTE KERCKHOFFS REVOL
Put it all together and you have: ENCRYPTION TECHNIQUES EVOLVED SLOWLY OVER THE CENTURIES AUGUSTE KERCKHOFFS REVOLUTIONISED THE WORLD OF CRYPTOGRAPHY WHEN AT THE END OF THE NINETEENTH CENTURY HE PUBLISHED A NUMBER OF PRINCIPLES THE MOST IMPORTANT PRINCIPLE STATED THAT THE METHOD OF ENCRYPTION ITSELF SHOULD NOT BE REQUIRED TO BE SECRET BUT THE STRENGTH SHOULD INSTEAD RELY UPON THE SECRECY OF THE KEY THIS PRINCIPLE IS JUST AS RELEVANT TODAY AS IT WAS THEN.
PS Hot on the heels of this post is the official answer from New Scientist which also revealed that I was one of the winners. They also explain the actual technique used for part 3. I broke it without spotting the simple pattern that makes it work and by making a 'lucky' guess.