2. 問題
何らかの文章（アスキーコード）を換字式暗号で暗号化した
列s = s1 . . . sn が与えられる．復号化せよ．
換字式暗号：
before after
a p
b c
c z
...
...
z m
before: s = “abababc”
⇓
after: T(s) =“pcpcpcz”
対応表T に従って一文字ずつ変換する（T は非公開）
1/ 23
16. 実験
言語モデルのためのコーパスは Project Gutenberg から
• The Adventures of Sharlock Holmes, by Arthur Conan Doyle
• Alice’s Adventures in Wonderland, by Lewis Carroll
• Pride and Prejudice, by Jane Austin
• The Old Testament of the King James Version of the Bible
をダウンロードして使用，違いを観察する
タブーサーチの初期解は頻度から貪欲法で生成
反復数は，解を見ながら適当に打ち切る（1000回程度）
近傍は２要素の交換で生成，近傍サイズw = 100程度
履歴サイズh = 10 程度使用
（計算時間はどれも数十秒∼数分程度）
次頁より，結果を真の解と比較（赤字は復元ミス）
15/ 23
17. by Adventure of Sherlock Holmes
”You see, my dear Watson,” II he propped his testItube in
the rack, and began to lecture with the air of a professor
addressing his class II ”it is not really difficult to construct
a series of inferences, each dependent upon its predecessor
and each simple in itself. Of, after doing so, one simply
knocks out all the central inferences and presents one’s
audience with the startingIpoint and the conclusion, one
may produce a startling, though possibly a meretricious,
effect. How, it was not really difficult, by an inspection of
the groove between your left forefinger and thumb, to feel
sure that you did HEA propose to invest your small capital
in the gold fields.”
16/ 23
18. by Alice’s Adventure in Wonderland
’You see, my dear Hatson,’ II he propped his testItube in
the rack, and began to lecture with the air of a professor
addressing his class II ’it is not really difficult to construct a
series of inferences, each dependent upon its predecessor
and each simple in itself. Af, after doing so, one simply
knocks out all the central inferences and presents one-s
audience with the startingIpoint and the conclusion, one
may produce a startling, though possibly a meretricious,
effect. Mow, it was not really difficult, by an inspection of
the groove between your left forefinger and thumb, to feel
sure that you did MER propose to invest your small capital
in the gold fields.’
17/ 23
19. by Pride and Prejudice
”You see, my dear Datson,” he propped his test tube in
the rack, and began to lecture with the air of a professor
addressing his class ”it is not really difficult to construct
a series of inferences, each dependent upon its predecessor
and each simple in itself. If, after doing so, one simply
knocks out all the central inferences and presents one’s
audience with the starting point and the conclusion, one
may produce a startling, though possibly a meretricious,
effect. Cow, it was not really difficult, by an inspection of
the groove between your left forefinger and thumb, to feel
sure that you did CO; propose to invest your small capital
in the gold fields.”
18/ 23
20. by The Bible
)Gou see, my dear Satson,) 22 he propped his test2tube in
the rack, and began to lecture with the air of a professor
addressing his class 22 )it is not really difficult to construct
a series of inferences, each dependent upon its predecessor
and each simple in itself; If, after doing so, one simply
knocks out all the central inferences and presents one’s
audience with the starting2point and the conclusion, one
may produce a startling, though possibly a meretricious,
effect; Low, it was not really difficult, by an inspection of
the groove between your left forefinger and thumb, to feel
sure that you did LOD propose to invest your small capital
in the gold fields;)
19/ 23
21. by The Bible; 青地は原文に未出現単語
)Gou see, my dear Satson,) 22 he propped his test2tube in
the rack, and began to lecture with the air of a professor
addressing his class 22 )it is not really difficult to construct
a series of inferences, each dependent upon its predecessor
and each simple in itself; If, after doing so, one simply
knocks out all the central inferences and presents one’s
audience with the starting2point and the conclusion, one
may produce a startling, though possibly a meretricious,
effect; Low, it was not really difficult, by an inspection of
the groove between your left forefinger and thumb, to feel
sure that you did LOD propose to invest your small capital
in the gold fields;)
20/ 23
24. 参考文献２：尤度最大化
• W. S. Forsyth and R. Safavi-Naini (1993):
Automated cryptanalysis of substitution ciphers. Cryptologia, 17,
4:407-418. 焼き鈍しで換字式暗号を解く
• R. Spillman, M. Janssen, B. Nelson, and M. Kepner (1993):
Use of a genetic algorithm in the cryptanalysis of simple
substitution ciphers. Cryptologia, 17: 1:31-44. 遺伝的アルゴリズム
で解く
• A. K. Verma, M. Dave, and R. C. Joshi (2007):
Genetic algorithm and babu search attack on the mono-alphabetic
subsitution cipher in adhoc networks. タブーサーチで解く
• P. Diaconis (2009): The markov chain monte carlo revolution.
Bulletin of the American Mathematical Society, 46, 2:179-205.
MCMCで解く（≒焼きなまし）
23/ 23
