## Homework 2 (due 4/19) CSC 233

We finished chapter 1, and will start on chapter 2.

There were several handouts, including substitution cipher examples, and excel spreadsheet (xls, xlsm) for the substitution cipher (with analysis), and a substitution cipher handout with hints on breaking substitution ciphers. We also saw a modern cipherdisk variant of Alberti's disk and Trithemius' tabula recta (both Trithemius's version and a modern version).

We'll continue exploring Renaissance cryptography and the ill-named Vigenere cipher in particular.

Handing it in: You can hand in the written parts of your homework as hardcopies in class, or submit them to me via email (I do not use col for homework submission).

1. (Reading Assignment) Finish reading chapter 1 (if you have not done so already), and read chapter 2 up to and including the section on the Viennese Black Chamber, and feel free to continue reading the story of Charles Babbage and the Vigenere cipher.

2. (Recognizing languages, 15pt) You intercepted the four ciphertexts a) through d) below; you know that the original plaintexts are in English, German and French, indeed you know that they are excerpts from Jules Verne's Voyage au centre de la terre, Mark Twain's Connecticut Yankee, and Johann Goethe's Leiden des jungen Werther (so one of the sources was used twice). You also know that the ciphers used were simple (monoalphabetic) substitutions ciphers, transposition ciphers, or combinations of the two (e.g. first a substitution followed by a transposition, or a double transposition). For each ciphertext, determine the source (Verne, Twain, Goethe) by determining which language the underlying plaintext is in without breaking the cipher. In particular, you  do not have to find out which particular cryptosystem was used.

a) "TEUCO FEELA WISOE SLWTI CSFTT SSBNU ONNAH AQFAD GEOSO IVBLL OSCNO OHHAH TSRNE DAETL URLES EGTIO HETWT TNLHF RIAAE YOGOP UUVES TTTHT IEUER LEREI SILLE HNSKH SMHAL DIETO UTHNT KMSTH OEAHP OXACO DMORH UDOYA RSEBR TIOES IEGDL NHSED TNTAH AASBR ENMUO OABES RTCNT ODMSR OTWAE NOLHS NNUEA UTYRR NEFEG TRADU BUYTN HRTET EHESI IOERG FESUT EGETR EOOLY ORMEA ESOGI DGWNO LCHTO IADWH HDLEO AFIEW DEGLN HDBSA HPILD RODWE VEDNM LATAF LSTES HREET EOHWI CHSAT OHATI WNDYE TTTOA EFESH DRNEI USINR IIRGG TGXMD VOTTD LBUFT OAMRE MNAOY YSHRE HTSEN APELT OREWO TDOON HAIIE EMYGL UTOYE TESTG TEUSR ALGER

b) "DOUHI RNAEB DFSED TTMES GUEEE LNLRM LDHNM SAKIW SESBE IRSNC TTVHN IOSES NTRAA DLHEI PPEHT NEEBD GNNRZ NLFLG NAIEE RLIHT DNMEE FDNNH MGENS IFEHT DLRIA EEUEE ABREG BNIME ENDNR GEIZS RSDUH TESDN NCSIE UTDEV ESSRE EGNRR RETHE LUZUE NENGD IAEMC UNAHS NESTL EINRS TGIHN EEENN RSNUH ELEEE IRIIC SCNHC HEEHB RAATN EKIDN LCANL DEIAE IZCGH DLSTN NIDNT EEIRR RGIGN FTEDH WAEEI NITNG EGDEN ANCTG SIAIH BIHLE TTLWS ETOII EGCNT NILUE NOEFR NRAFA EITAE METSE COTNC"

c) "ARTAB EGEJL AFAFL AGDBE HNBBQ KAGGG IKHRI ACEBF DDABF ABREF KDQGT AAJIH EUFEF IGGFD IFKGQ DHBFD GEPJE BCHEG JEBDI AGRGH DRCEI DJAEG QEOGA JHIOA DBABH BCDBB DHKBB JNGEB GEDMS FDFDB MDPIF EQYGL SBIGF ABSFB GABBI UAGEB RMFDB MBFEI KEDID ENRJA AFHKL MIMOE LHGAA LHMDD KCEPO RNLBI BLEIA ABMNI CKKNI HPRJA DGNAO GDCJF AOGAD EDNPD IKCBB IDAOM EJNEC CADAB HDDER FDCGC GDDSL SDCJT OBCTA IFGLB IAEFF FJTDF CGFID BBJIF KJBHL GHFKI CFFFC CPKAB PO"

d) "ASREA GEUAI UOGUO TLAET BETRV TONER SAIUQ LUNIO GUDIE NHEBY DRARR EAMCT PNUAN RNTAR RPNRO CSESN TJOEL DNOAV ETUES SNNOR RLNTA ULEUE VIILI OEIOE SRTUT SUTAI OORHE SEDRE UNIAE FIENE IMNFS CLCES TARNO UNUET ELMIT ONTED ANPUM RBLNU SESEN AIPEA EIVEM CCLLA OIULO ODSSI MENXC NDUUE ANTND PMSRC OSUAE LCVAZ PTCIS URNVS ESALE ALNUA DEGME EGTAF DBAPU NXNIS EJIOE SRHRP RINEL ALUAS ETTIM TIEUS IAETI DSNET UPPNR UNIEL RENPM ETQES USTTA TELTL DEITN ROMFE SALRE DEEPT RTETC MRERA TANTL AEAUE EAMPU NRRRA SRRNE DAEST OEENE OCLIA LTUUN ATAAN ISOOP ERIBE ELUUC GSUIE AEEIC EISMA DPEPM EANDN ARRAA NJALP RTTON LOOLN PONEM ECJEX STRPS SNS"

Hint: think frequency analysis; you can use the substitution cipher spreadsheet to perform a frequency analysis. For extra credit determine in each case whether the system used was simple substitution, simple transposition, or a combination of both.

3. (Substitution Cipher, 25pt) Your goal is to break a substitution cipher. Enter your last name below and hit return to get your ciphertext. The ciphertext will be different each time you submit the form (since I use a random substitution), but your plaintext does not change. Attack the cipher with the tools mentioned in class and in the book.

You can use the substitution cipher tool (xls, xlsm) to help you with the analysis (or download and use the tool from Simon Singh's Code Book CD). In the column called cipher you can enter letters to substitute for the corresponding letters in column F. The "encode" and "decode" buttons will perform the substitutions accordingly.

The "analyze ciphertext" button will determine the relative frequencies of letters in the ciphertext. After hitting that button you should sort rows 5-30 in columns H/I in descending order by column I, so you get a first, rough order of the letters by frequency.

You can also enter text in cell I1, and hit the "Count" button to count how often  that text occurs within the ciphertext. That'll help you with determining bigram and trigram frequencies.

Last Name:

When writing up your solution, include details about how you proceeded, including information about what decisions you made, why you made them, and (if necessary), why you went back on an earlier decision.

Also include intermediary snapshots of the plaintext as you have it reconstructed (similar to how the book does it).

Note: do submit your solution even if you don't manage to break the cipher entirely. There will be partial credit.

4. [Extra Credit] Decrypt the following ciphertext which is the result of a monoalphabetic substitution cipher together with removing all punctuation and word breaks. (This will be tricky.) For convenience, letters are grouped into groups of ten.

OBATTAIEPN JKAOBTTCUT EVIEPNGEDT AOBTNVRNTU TEJKAOBTDQ LAJCKADNIE OBTIABLCCN

KJNOKETEIE TJKAHKAOLC HTEDKKHTDO KDITKETJKA OBTDLAVCKA DKEBINDLAV OBAKETIEOB

TCLEDKJHKA DKAQBTATOB TNBLDKQNCI TKETAIEPOK AGCTOBTHLC CKETAIEPOK JIEDOBTHKE

TAIEPOKSAI EPOBTHLCCL EDIEOBTDLA VETNNSIEDO BTHIEOBTCL EDKJHKADKA QBTATOBTNB LDKQ

NCIT

Marcus Schaefer
Last updated: April 13th, 2011.