Breaking the code on Homework 3

This post is not required. However, I wanted to catalog my experience breaking the code given in Homework 3 and I figured, "What better place to do this than on my blog?"

I was given the following CODE to break:

TIFSYCUG YIVSCYIT B XBYUCFSLBY KCPJTIU TIFSYCUG
XYEHITTCEPBLT BU LIBTU URI ZEEJ EPIT TII URI MEYLJ JCHHIYIPULG URIG
FBPU MBLO CPUE B TUEYI MCURESU PEUCFCPZ REM URIG KCZRU TREXLCHU URIG
FBPU STI B FEKXSUIY MCURESU MEPJIYCPZ BNESU URI TIFSYCUG
DSLPIYBNCLCUCIT URIG FBPU DEUI MCURESU UYGCPZ UE HCZSYI ESU REM UE
DEUI UMCFI URIG QSTU FBPU RILX CU URCT OCPJ EH URCPOCPZ CT PEU
PBUSYBL HEY KETU XIEXLI CUT PEU PBUSYBL HEY IPZCPIIYT ZEEJ
IPZCPIIYCPZ CPDELDIT URCPOCPZ BNESU REM URCPZT FBP NI KBJI UE MEYO
URI TIFSYCUG KCPJTIU CPDELDIT URCPOCPZ BNESU REM URCPZT FBP NI KBJI
UE HBCL CU CPDELDIT URCPOCPZ LCOI BP BUUBFOIY BP BJDIYTBYG EY B
FYCKCPBL GES JEPU RBDI UE IAXLECU URI DSLPIYBNCLCUCIT GES HCPJ NSU
CH GES JEPU TII URI MEYLJ URBU MBG GESLL PIDIY PEUCFI KETU TIFSYCUG
XYENLIKT

As you can see, it makes little sense. I started examining it on paper, looking for multiple appearances of the same word, for example.I first noticed that the most frequent letter was U. I tried substituting the letter E in for U, but discovered that U wouldn't work because then UE would have to translate to a word with E as the first letter. There aren't very many good candidates for a word that begins with E. So I ruled out E going to U. Then I tried E going to the second most frequent letter: I. Making that substitution led me to notice that URI and URIG appeared pretty frequently. I figured that whatever words they represented, they had the first three letters in common. I looked up words that are four letters long, had E in the fourth position (and only in the fourth position) and in which the first three letters were also a word. I came up with a list of about 12 words, among them were THEN, THEY, THEM. I tried putting in the appropriate substitutions with THEN but found words that ended with TN. So I switched and tried THEY. It fixed the TN problem. I then noticed that TIFSYCUG would then translate back to TeFSYCty. I looked up words that were eight letters long and had e and ty in the appropriate positions. I found a list of six words, among SECURITY. I tried the appropriate substitutions and started to see other words appear. ATTACKER became apparent, followed by a long list of other words. As new words became apparent I finished decyphering them. The results led to more words. Eventually I decyphered the whole message, resulting in:

SECURITY REQUIRES A PARTICULAR MINDSET SECURITY

PROFESSIONALS AT LEAST THE GOOD ONES SEE THE WORLD DIFFERENTLY THEY

CANT WALK INTO A STORE WITHOUT NOTICING HOW THEY MIGHT SHOPLIFT THEY

CANT USE A COMPUTER WITHOUT WONDERING ABOUT THE SECURITY

VULNERABILITIES THEY CANT VOTE WITHOUT TRYING TO FIGURE OUT HOW TO

VOTE TWICE THEY JUST CANT HELP IT THIS KIND OF THINKING IS NOT

NATURAL FOR MOST PEOPLE ITS NOT NATURAL FOR ENGINEERS GOOD

ENGINEERING INVOLVES THINKING ABOUT HOW THINGS CAN BE MADE TO WORK

THE SECURITY MINDSET INVOLVES THINKING ABOUT HOW THINGS CAN BE MADE

TO FAIL IT INVOLVES THINKING LIKE AN ATTACKER AN ADVERSARY OR A

CRIMINAL YOU DONT HAVE TO EXPLOIT THE VULNERABILITIES YOU FIND BUT

IF YOU DONT SEE THE WORLD THAT WAY YOULL NEVER NOTICE MOST SECURITY

PROBLEMS