**Chapter 9**
1. Complete the decipherment of the Red training exercise begun in this chapter. Warning! The encipherer made several errors.
2. If the sixes alphabets and the twenties alphabets are all known for Red, but a given message may start with any one of those alphabets for each group of letters, how many possible starting positions are there altogether?
3. If the sixes for Purple are E, H, K, P, R, and S, what is the average frequency for the sixes and what is the average frequency of the twenties? Base your answer on the frequencies provided in Chapter 2.
4. If the sixes for Purple are B, D, K, N, S, and W, what is the average frequency for the sixes and what is the average frequency of the twenties? Base your answer on the frequencies provided in Chapter 2.
5. From the Purple ciphertext below, determine the sixes and twenties.^{6}
NHSG DZAQ SEVG MAES VESH AJGL AOMZ OFBE EBFG OLOQ ITEB ZAET QAHE AUVY VHHV ONTO HNNN BMEM IHUL IVOE ENSC SOAO HPDN HPAH ZHNH QHES OAOD XXOQ CATO UEOP AHEF DOEV EHES AEMA TSAR YFNA DHXT OHSJ OHJA WAKH WEHM TXQE JHLH EMEL EIJU AVAN PADN KESG ESLH OJSS ONOO IBUS QYWG YSOV SHPS EWNH ASKM AJAK TIPB JRXR HDZO DBSP TGIG ESZS HDLN CHBD NUAA TONE CYDN BDSI MOQK HNNY SHNN FTBS GXAC MSLG DSHJ OSOA JLXE QFNU LOWL SOIS AOOJ HOAI WMNC UHZB NMZO NUUN SZOO SANJ ESEZ ZISJ KSYQ AXDS KNSO OVHO PEDA PSFO DXPP XSAA ETZO ISMV AWHT HZES GESH RQZH RROJ QARC EBEB THGD EOOG MUAC VHDD HQYN AZOJ HONO EQNC QHBO IBSO JEAI EOLE UTON OLEO SNAJ AAXX HUMH XCLE RSSA QAWY FHHS PYOE OTSR QSSH VANN SXEV AOHE TSSL CKBW AMAO LHOB AKTR BJTD XOEV VHRZ AHYK HTZR SCGM EUEA LSRE NYNF EHKL HEFA KZWS QSPC CLAN PKOL XIEE EOCD NZFG OHTA AKSO CODA AANH SGHE OSOZ EHWX YNNE IHPO WIEH EYHO GOSS IWON MEVA AJCL POEB RAWZ OMWQ AZHX GTIF HPXE HYME NEAE EQNA ZNYF STOE BNSC CVSQ OHDA ERSS QCVJ HJOZ GOZH AKAO RXAX NROL EUMS GFNQ SZOW AOLE MHUS OZGO UEFU SCES IEES ZGAA LSSA UTSB AEMG EEOQ ZRAR EOCE BONZ KNQN EHMN LODA NHKX HNUN FFNK IBVN HESD FOGE X
6. From the Purple ciphertext below, determine the sixes and twenties.^{7}
RCDK HBYM KDEU RYQX HJZZ BQGO XRSR ETYP NZFQ COBA EHYQ YCNJ XKED HTJU TWSP HJQQ BPYK KSOZ XCEQ BLJH XTSW QUPR QXMJ KBEA NUMG QHIE EVQZ IPBF BUZY SKFR WEDZ MKWS RVSM PKGG NZQK NLYH FSSB AKCG CEAI YRET WNVN LYWL ZLQO ZCUG NUQK JGOC UFRH HQMC YKZS ENFL FOTR KWVT SOTE ENZX TJMC VILV UDKZ JCPQ QOHM VHHQ EAMP JBKF NTWZ WEMJ OVRS SXUY KYOR SIQY NVGQ RUNP URPL XLUU QZGD XASZ BGAZ SKOG BTFE MVCZ RAWM IKKJ YKCO OYOM VKDY VSYC FQIY JCUY HLDR PEQP YYWS THEF SJHH DTFC AOYN VSHX SBCK ONNE HVME AUQN LJJE SNIG NKVR TXKN IKZE EIKC YULQ QVBR JKKW XHOX UHQT VZKC GNOS FEPE LAQM GQJL BHEB SSYM KZGD SSXO RNDY LKZQ PCFE NRGM OGBB NSOO RDWP WDNA MIXW ERPN KNBB GWRV YEZH AMKM YESY AEGY XETA ZGDH HJVU OCUX UBES OIEB SKIQ KLXK RFNE ZURW HNJT TIJS DDUJ HPRN HTHI XJKZ FKPZ MOPJ SFRD KHTE XEBB ALKD MBJB OHHG SVVI WOJF CHWO XVCH KKWK MQHY ORNQ INQK PRWP AQOK XIOQ LCMP QZRE SBLA NAMZ HCRJ XINH WKAR PXJN FTMH EVXE ASZM GEXT ZQJK XLGN WBNS DUGN MHZM EQQZ JKQG HFOV OLUH XNUH RBIE SIXI WWPL SJES ARBW WESA TZTU EDOM ZNYG QMBB HYDN HNSU QDGO NEXV FYKK QPKU LKPR GEDD NVEM VEWB EQKC HVRW VKHC BVMH ENDA QGBI SQAE GYCG MTSQ IALI KEUU XTEV NSUQ MMBU NBNQ VSFJ MQEN PICK NTAL ASQU SWWC NHFO YSKC KYQK KIUS HDUQ LUDX CQKY NCFP QDDN DGPP KKQW EKWJ IIWB BAQE HOLC KZEF XVHS NFIH GFWM AKNN MAZK FVTM SXUD LMBT FCZU AEBP HELF KZHA JNEL WYOO DZIE NLAL PIAG NNTQ GBCF IQDB QKWQ NGQH HOGY VNIF QMFN RLSN EFBL YWTC KMAV CAAF RFSR HOZX EQWF DAZO CUHA UCRB NOHL EIMJ HETG KMGA SSTS JPMQ MSHV DGMD SPGX BKXB JHQK CMYD GTBC QKIA VGUC JEFQ KAAQ DSQZ KTWA HWDK EOGH DJIK KJRB MKWQ ZKQU SQIF DQKH AFOE MLCK OGJQ WMOQ VNSP E
7. Select the sixes in such a way that their average frequency is as close as possible to the average frequency of the twenties. Would this be desirable?
8. If you have a known plaintext and the corresponding ciphertext in Purple, and the sixes were chosen to be the vowels, how many of these vowels would have to be present (at a minimum) in the messages to uniquely determine all 25 substitution for the sixes? Is there a maximum value? Using the minimum, and the average percentage of vowels in a given message, what is the expected length of the message needed? For the sake of this problem, assume that the message is in English.
9. Suppose you have determined that the sixes for a Purple message are given by E, Q, A, D, R, and H and the partial decipherment of a message is
Ciphertext BRAXEFQCEVQOOXHECFDLNHQRVQPPLCERP
Message -HE-A-A-E-E---ER--E--REQ-E----HA-
Use context and word patterns (not math!) to fill in the missing letters. To make the exercise easier, the plaintext is in English.
10. Suppose you have determined the first ten cycle 1 alphabets for the Purple machine and the first cycle 2 alphabet. Your results appear below. Assume the machine is in a configuration such that the second pattern observed by Genevieve Grotjan holds and use this pattern to determine alphabets 2 through 10 for cycle 2.
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