For the key on this assignment, you do not need to come up with a word or phrase that shuffles the columns appropriately, but you do need to give the number labels. So if the writer's keyword was KILROY, you would put 2 1 3 5 4 6. (Note that the labels are out of order on the plaintext, and in order on the ciphertext. Don't mix that up.)

The kinds of thought processes you should explain are how you chose the rectangle to use, and which things you noticed that suggested the order of columns, and how you confirmed that guess. You may not use programs that make these decisions for you (unless you write them yourself), but you may use programs that automate repetitious work or that keep details straight, including the following:

You can use this site or this site to rearrange columns in your browser, or this site to do the same a little less graphically. If you use any other online tools, test them first to make sure the transposition they do is the one we're using. Some do, some don't.

In particular, do not use this site for your homework. Don't. Don't. Do not. Don't. It does not do the same transposition as we do, and if you use it you will never ever break the message. I warn students about this every semester, but there are occasionally submissions that ignore this warning.

HHWSM IWNER EEOAE EIMDL BNGMU AEOAU TUOLD TETSD PCELE HAMCT LTBTE ROEUU HONEF IDAAA MOSER APEER TMFIN WLNGS LGIOR LSHDE YSNTA TSPHD AINQM EDVRN TMIEI OOSNN DDMSA NEARB ARILC SOIIT ELCED EUWEI EOOFA ARSFO RENEO UHELC GSRAL LENYB HNMRS TEHTS HSDCW EHMOE WTEIT ATAWO TRYFD HTDOO YIDUO SHTMT DOWDU NSIAY RAWCD TROLE LTIIE EFYOK TIIHO REESH AUEYE EOSHO CADRG TSGAY IOEON BNELB TYNFD RTESE LRTAF TAYDD LNAEN HREEI PAEFV HANAE LSFBO OUGSH AIUAS SFISF ANRAN DIFEO IIYDI DWGRA UTASF YIURD EBCIW RNSOR NIDEE STRAT EHSHS INRFW DEDNT UEGVM FIHTI RPOAI YHIOI SDTNO FR

In your analysis, make sure to indicate:

• How you determined the possible box sizes
• How you selected box sizes for further analysis
• How you located some adjacent columns during decipherment

Critical Thinking:

Suppose we were an organization using this kind of cipher as our standard way of communicating secretly. While keeping Kerckhoff's principle in mind (only your key and message are secret, not the choice of cryptosystem itself), consider the following proposal to alter the cryptosystem used above:

We use a standard public codebook to replace common words and phrases with abbreviations, thus greatly reducing the length of the plaintext before we encipher it with a columnar transposition as above.

Here are examples of possible abbreviations (you probably know a lot more than I do...):

as soon as possible -> asap brother -> bro please -> pls never mind -> nm

Would the change to the cryptosystem make it more secure (take significantly more time to cryptanalyze, mitigating an existing weakness), less secure (take significantly less time to cryptanalyze, create a new major weakness), or neither (only trivial change, no major impact on strengths or weaknesses).

Why? How? What strengths/weaknesses change?