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102 CHAPTER 6. DECRYPTING MONOALPHABETIC CIPHERS 6.6 Topics and Techniques 1. Of the etaoinshr letters (a) Which three appear frequently both as initial and final letters (b) Which three appear frequently as final letters, but less so as initial letters (c) Which three appear frequently as initial letters, but less so as final letters (d) Which four are most likely to make doubles 2. Which are the most common vowel-vowel combinations Are they actually very common 3. Which letters do vowels prefer to associate with What about consonants 4. Which (type of) letters are the friendliest, associating with almost all others Which are most discriminating, preferring the company of only a few other letters 5. Are ciphertexts that retain their word breaks easier or harder to decrypt Explain why. 6. What is a digraph table How to construct one What does it tell us 7. What is a homophone 8. Why can ciphers that involve homophones be more secure than those without 9. What is a null How do nulls make the cryptanalyst’s life more difficult 6.7 Exercises 1. Decrypt the following cipher. UN MGHHYV LNS VYETEHGUH HLY KVQFHNCVGM GDD HLGH TE VYGDDQ UYYRYR TE GU YUHVQ HLY TRYUHTATKGHTNU NA NUY SNVR NV NA HLVYY NV ANPV DYHHYVE LYDYU ANPKLY CGTUYE Frequency count: A B C D E F G H I J K L M N O P Q R S T U V W X Y Z 5 0 2 6 6 1 9 15 0 0 3 7 2 12 0 2 3 4 2 8 10 12 0 0 19 0 2. Decrypt the following cipher. GNLTA DTPUH IOHJQ BTCNJ QHCVN DQPIQ ZNDCN ZJTGD TQHIQ TWWHO TIGTH IQBTF NDWLQ NLPSH QVDNL XGTJC XGBCN DTPIL CXGBC NDTQD XJQFN DQBSH IZNDC PQHNI QBPIJ VHTJ
6.7. EXERCISES 103 Frequency count: A B C D E F G H I J K L M N O P Q R S T U V W X Y Z 1 6 8 11 0 2 7 10 9 7 0 4 0 13 2 6 14 0 2 13 1 2 3 4 0 3 3. Decrypt the following cipher. PYJQG KYUQR CQEQR LOTGQ RQTRT RYTAH KYLTE HAWEJ QRWHQ RCTAW UHEWR PQAYW UQKWV YDWEH YPNGT RQHLT UYHQL YHKWR QHPYE YUVYE JKWUF YEBWB BWCY Frequency count: A B C D E F G H I J K L M N O P Q R S T U V W X Y Z 4 3 3 1 8 1 3 9 0 3 5 4 0 1 1 4 13 10 0 8 6 2 11 0 14 0 4. Fletcher Pratt used a Keyword Cipher to encipher the following message. Can you decrypt it, and recover the keyword SZPQP ERHKQ PCRKJ VZXPU PJSZP GKRSC GCSPT QIQXL SKNQC LZPQR ZXTFN ZPRES CSPFK JNKUP QCRDG LFPRT HRSES TSEKJ IELZP Q 5. Decrypt the following cipher. AOPBO GDGPG DUKLD NWCTD OALTQ NGUMT AEDKR WDLWG WCUTD MDKAZ ZCGGC TOUFG WCNZA DKGCH GGASC KCDGW CTODK MZQUT DKMTU PNOUF LUKOG AKGZC KMGWW AXCBC CKTCN ZALCV BQUGW CTZCG GCTOF DMPTC OODMK OUTLU EBDKA GDUKO UFGWC EDKAL LUTVA KLCRD GWAVC FDKDG COQOG CEAKV SCQ. Frequency count: A B C D E F G H I J K L M N O P Q R S T U V W X Y Z 14 4 25 20 4 5 23 1 0 0 18 9 7 5 14 4 5 2 2 14 14 4 11 1 0 7 6. Among the techniques the British used during the Revolutionary War was a relatively simple monoalphabetic cipher. It was apparently used by Sir Henry Clinton, the commander-in-chief of His Majesty’s Forces in North America from 1778 to 1782. Decrypt the following fragment of a letter sent in this cipher. 75 62 55 67 77 68 74 69 71 68 69 68 72 55 54 73 62 55 66 61 73 73 55 71 73 68 66 55 63 73 62 68 74 61 62 73 63 62 51 54 60 74 65 65 77 55 76 89 65 51 63 67 55 54 66 77 72 55 65 60 Hint: start with a frequency count of the pairs of numbers. 7. A technique for making a monoalphabetic cipher with homophones is to take a long word or phrase, number the letters in order of appearance, and then use those numbers as substitutes for the letters. Any letters that do not appear are numbered at consecutively at the end. (This method apparently originated with the Argenti’s [Kahn, 113].) In a letter on 9 Oct 1863 from 1st Lt. Stephen M. Routh, Chief Signal Officer of the District of West Louisiana, Confederate Army, to Maj. Gen.
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Cryptology: An Historical Introduct
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Contents List of Figures 8 1 Caesar
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CONTENTS 5 9 Digraphic Ciphers 167
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List of Figures 1.1 Saint Cyr Slide
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Chapter 1 Caesar Ciphers There are
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11 Examples: Encipher or decipher t
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1.1. SAINT CYR SLIDE 13 paper turne
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1.3. FREQUENCY ANALYSIS 15 PX PBEE
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1.3. FREQUENCY ANALYSIS 17 A bit mo
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1.3. FREQUENCY ANALYSIS 19 Examples
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1.4. LINQUIST’S METHOD 21 the cip
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1.7. EXERCISES 23 12. What is the m
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1.7. EXERCISES 25 (d) VTXLTKBTG LXV
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1.7. EXERCISES 27 (d) IKSUT JKIOT K
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Chapter 2 Cryptologic Terms Cryptog
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Chapter 3 The Introduction of Numbe
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3.1. THE REMAINDER OPERATOR 33 Exam
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3.1. THE REMAINDER OPERATOR 35 Perf
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3.1. THE REMAINDER OPERATOR 37 As a
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3.2. MODULAR ARITHMETIC 39 While %
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3.3. DECIMATION CIPHERS 41 previous
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3.4. DECIPHERING DECIMATION CIPHERS
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3.6. KOBLITZ’S KID-RSA AND PUBLIC
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3.6. KOBLITZ’S KID-RSA AND PUBLIC
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3.9. EXERCISES 49 8. How do we enci
Page 51 and 52: 3.9. EXERCISES 51 (c) Encipher 54 4
Page 53 and 54: 3.9. EXERCISES 53 (b) Encipher secr
Page 55 and 56: Chapter 4 The Euclidean Algorithm I
Page 57 and 58: 4.2. GCD’S AND THE EUCLIDEAN ALGO
Page 59 and 60: 4.3. MULTIPLICATIVE INVERSES 59 (2)
Page 61 and 62: 4.3. MULTIPLICATIVE INVERSES 61 (2)
Page 63 and 64: 4.4. DECIPHERING DECIMATION AND LIN
Page 65 and 66: 4.5. BREAKING DECIMATION AND LINEAR
Page 67 and 68: 4.6. SUMMARY 67 To put it more blun
Page 69 and 70: 4.8. EXERCISES 69 5. Here we work w
Page 71 and 72: Chapter 5 Monoalphabetic Ciphers He
Page 73 and 74: 5.2. KEYWORD MIXED CIPHERS 73 Examp
Page 75 and 76: 5.4. INTERRUPTED KEYWORD CIPHERS 75
Page 77 and 78: 5.6. BASIC LETTER CHARACTERISTICS 7
Page 79 and 80: 5.7. ARISTOCRATS 79 the 69971 or 42
Page 81 and 82: 5.9. TOPICS AND TECHNIQUES 81 5.9 T
Page 83 and 84: 5.10. EXERCISES 83 (h) DYVTP KKIQ.
Page 85 and 86: 5.10. EXERCISES 85 13. Ciphers in w
Page 87 and 88: 5.10. EXERCISES 87 17. General Pier
Page 89 and 90: Chapter 6 Decrypting Monoalphabetic
Page 91 and 92: 6.2. DECRYPTING MONOALPHABETIC CIPH
Page 97 and 98: 6.3. SUKHOTIN’S METHOD FOR FINDIN
Page 99 and 100: 6.4. FINAL MONOALPHABETIC TRICKS 99
Page 101: 6.5. SUMMARY 101 our ciphertext muc
Page 105 and 106: 6.7. EXERCISES 105 53++!305))6*;482
Page 107 and 108: 6.7. EXERCISES 107 93 93 82 48 39 6
Page 109 and 110: Chapter 7 Vigenère Ciphers It was
Page 111 and 112: 7.2. TRITHEMIUS, THE FATHER OF BIBL
Page 113 and 114: 7.3. BELASO, THE UNKNOWN AND PORTA,
Page 115 and 116: 7.4. VIGENÈRE CIPHERS 115 to encip
Page 117 and 118: 7.6. HOW TO BREAK VIGENÈRE CIPHERS
Page 119 and 120: 7.6. HOW TO BREAK VIGENÈRE CIPHERS
Page 121 and 122: 7.7. THE KASISKI TEST 121 Kasiski
Page 123 and 124: 7.8. SUMMARY 123 Repetition Start P
Page 125 and 126: 7.10. EXERCISES 125 2. Little Miss
Page 127 and 128: 7.10. EXERCISES 127 to Gen. E. K. S
Page 129 and 130: 7.10. EXERCISES 129 MEJMY JKXCD LCN
Page 131 and 132: 7.10. EXERCISES 131 22. (a) Use Kas
Page 133 and 134: 7.10. EXERCISES 133 (a) Construct a
Page 135 and 136: Chapter 8 Polyalphabetic Ciphers Th
Page 137 and 138: 8.1. COINCIDENCES 137 (being born o
Page 139 and 140: 8.2. THE MEASURE OF ROUGHNESS 139 I
Page 141 and 142: 8.2. THE MEASURE OF ROUGHNESS 141 P
Page 143 and 144: 8.3. THE FRIEDMAN TEST 143 The Frie
Page 145 and 146: 8.4. MULTIPLE ENCIPHERINGS 145 Bein
Page 147 and 148: 8.4. MULTIPLE ENCIPHERINGS 147 Just
Page 149 and 150: 8.5. VIGENÈRE’S AUTO KEY CIPHER
Page 151 and 152: 8.5. VIGENÈRE’S AUTO KEY CIPHER
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8.6. PERFECT SECRECY 153 invent now
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8.8. TERMS AND TOPICS 155 multiple
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8.9. EXERCISES 157 6. As is this on
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8.9. EXERCISES 159 13. It has been
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8.9. EXERCISES 161 This is Equation
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8.9. EXERCISES 163 A: AB CDE FGH I
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8.9. EXERCISES 165 26. Decipher SVQ
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Chapter 9 Digraphic Ciphers Althoug
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9.1. POLYGRAPHIC CIPHERS 169 f a g
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9.2. HILL CIPHERS 171 th 2.96 es 1.
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9.2. HILL CIPHERS 173 We will be us
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9.3. RECOGNIZING AND BREAKING POLYG
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9.4. PLAYFAIR 177 Playfair Ciphers:
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9.5. SUMMARY 179 9.5 Summary Polygr
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9.7. EXERCISES 181 (b) The use of
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9.7. EXERCISES 183 10. Just as we c
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9.7. EXERCISES 185 (d) (For those(
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9.7. EXERCISES 187 The rules that W
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Chapter 10 Transposition Ciphers In
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10.3. TURNING GRILLES 191 1 2 3 7 4
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10.4. COLUMNAR TRANSPOSITION 193 co
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10.5. TRANSPOSITION VS. SUBSTITUTIO
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10.6. LETTER CONNECTIONS 197 F 2 G
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10.7. BREAKING THE COLUMNAR TRANSPO
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10.8. DOUBLE TRANSPOSITION 201 Sinc
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10.9. TRANSPOSITION DURING THE CIVI
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10.9. TRANSPOSITION DURING THE CIVI
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10.10. THE BATTLE OF THE CIVIL WAR
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10.13. EXERCISES 209 14. What is a
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10.13. EXERCISES 211 and the second
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10.13. EXERCISES 213 evening Adam h
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10.13. EXERCISES 215 Several codewo
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10.13. EXERCISES 217 4. (which is t
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Chapter 11 Knapsack Ciphers Merkle
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11.3. AN EASY KNAPSACK PROBLEM 221
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11.4. THE KNAPSACK CIPHER SYSTEM 22
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11.4. THE KNAPSACK CIPHER SYSTEM 22
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11.5. PUBLIC KEY CIPHER 227 Even wi
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11.8. EXERCISES 229 2. Given the we
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Chapter 12 RSA Take two large prime
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12.1. FERMAT’S THEOREM 233 Exampl
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12.3. COMPLICATION II: A SUBSTANTIA
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12.3. COMPLICATION II: A SUBSTANTIA
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12.5. COMPLICATION IV: THE LAST ONE
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12.6. PUTTING IT ALL TOGETHER 241 1
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12.8. RSA 243 The RSA Algorithm Set
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12.9. RSA AND PUBLIC KEYS 245 There
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12.10. HOW TO BREAK RSA 247 had to
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12.12. SUMMARY 249 cannot read the
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12.14. EXERCISES 251 6. What is a
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12.14. EXERCISES 253 Bob is going t
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Bibliography [Antonucci] Michael An
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BIBLIOGRAPHY 257 [Shamir] [SRA] A.
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