summaryrefslogtreecommitdiff
path: root/lisp/play/decipher.el
blob: ade0d15006abb5aeb49f10a6e33293b4685f6ae7 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
;;; decipher.el --- cryptanalyze monoalphabetic substitution ciphers
;;
;; Copyright (C) 1995-1996, 2001-2012  Free Software Foundation, Inc.
;;
;; Author: Christopher J. Madsen <chris_madsen@geocities.com>
;; Keywords: games
;;
;; This file is part of GNU Emacs.
;;
;; GNU Emacs is free software: you can redistribute it and/or modify
;; it under the terms of the GNU General Public License as published by
;; the Free Software Foundation, either version 3 of the License, or
;; (at your option) any later version.

;; GNU Emacs is distributed in the hope that it will be useful,
;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
;; GNU General Public License for more details.

;; You should have received a copy of the GNU General Public License
;; along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.

;;; Commentary:
;;
;;; Quick Start:
;;
;; To decipher a message, type or load it into a buffer and type
;; `M-x decipher'.  This will format the buffer and place it into
;; Decipher mode.  You can save your work to a file with the normal
;; Emacs save commands; when you reload the file it will automatically
;; enter Decipher mode.
;;
;; I'm not going to discuss how to go about breaking a cipher; try
;; your local library for a book on cryptanalysis.  One book you might
;; find is:
;;   Cryptanalysis:  A study of ciphers and their solution
;;   Helen Fouche Gaines
;;   ISBN 0-486-20097-3

;; This package is designed to help you crack simple substitution
;; ciphers where one letter stands for another.  It works for ciphers
;; with or without word divisions.  (You must set the variable
;; decipher-ignore-spaces for ciphers without word divisions.)
;;
;; First, some quick definitions:
;;   ciphertext   The encrypted message (what you start with)
;;   plaintext    The decrypted message (what you are trying to get)
;;
;; Decipher mode displays ciphertext in uppercase and plaintext in
;; lowercase.  You must enter the plaintext in lowercase; uppercase
;; letters are interpreted as commands.  The ciphertext may be entered
;; in mixed case; `M-x decipher' will convert it to uppercase.
;;
;; Decipher mode depends on special characters in the first column of
;; each line.  The command `M-x decipher' inserts these characters for
;; you.  The characters and their meanings are:
;;   (   The plaintext & ciphertext alphabets on the first line
;;   )   The ciphertext & plaintext alphabets on the second line
;;   :   A line of ciphertext (with plaintext below)
;;   >   A line of plaintext  (with ciphertext above)
;;   %   A comment
;; Each line in the buffer MUST begin with one of these characters (or
;; be left blank).  In addition, comments beginning with `%!' are reserved
;; for checkpoints; see decipher-make-checkpoint & decipher-restore-checkpoint
;; for more information.
;;
;; While the cipher message may contain digits or punctuation, Decipher
;; mode will ignore these characters.
;;
;; The buffer is made read-only so it can't be modified by normal
;; Emacs commands.
;;
;; Decipher supports Font Lock mode.  To use it, you can also add
;;     (add-hook 'decipher-mode-hook 'turn-on-font-lock)
;; See the variable `decipher-font-lock-keywords' if you want to customize
;; the faces used.  I'd like to thank Simon Marshall for his help in making
;; Decipher work well with Font Lock.

;;; Things To Do:
;;
;; Email me if you have any suggestions or would like to help.
;; But be aware that I work on Decipher only sporadically.
;;
;; 1. The consonant-line shortcut
;; 2. More functions for analyzing ciphertext

;;;===================================================================
;;; Variables:
;;;===================================================================

(eval-when-compile (require 'cl-lib))

(defgroup decipher nil
  "Cryptanalyze monoalphabetic substitution ciphers."
  :prefix "decipher-"
  :group 'games)

(defcustom decipher-force-uppercase t
  "Non-nil means to convert ciphertext to uppercase.
nil means the case of the ciphertext is preserved.
This variable must be set before typing `\\[decipher]'."
  :type 'boolean
  :group 'decipher)


(defcustom decipher-ignore-spaces nil
  "Non-nil means to ignore spaces and punctuation when counting digrams.
You should set this to nil if the cipher message is divided into words,
or t if it is not.
This variable is buffer-local."
  :type 'boolean
  :group 'decipher)
(make-variable-buffer-local 'decipher-ignore-spaces)

(defcustom decipher-undo-limit 5000
  "The maximum number of entries in the undo list.
When the undo list exceeds this number, 100 entries are deleted from
the tail of the list."
  :type 'integer
  :group 'decipher)

(defcustom decipher-mode-hook nil
  "Hook to run upon entry to decipher."
  :type 'hook
  :group 'decipher)

;; End of user modifiable variables
;;--------------------------------------------------------------------

(defvar decipher-font-lock-keywords
  '(("^:.*"  . font-lock-keyword-face)
    ("^>.*"  . font-lock-string-face)
    ("^%!.*" . font-lock-constant-face)
    ("^%.*"  . font-lock-comment-face)
    ("\\`(\\([a-z]+\\) +\\([A-Z]+\\)"
     (1 font-lock-string-face)
     (2 font-lock-keyword-face))
    ("^)\\([A-Z ]+\\)\\([a-z ]+\\)"
     (1 font-lock-keyword-face)
     (2 font-lock-string-face)))
  "Font Lock keywords for Decipher mode.")

(defvar decipher-mode-map
  (let ((map (make-keymap)))
    (suppress-keymap map)
    (define-key map "A" 'decipher-show-alphabet)
    (define-key map "C" 'decipher-complete-alphabet)
    (define-key map "D" 'decipher-digram-list)
    (define-key map "F" 'decipher-frequency-count)
    (define-key map "M" 'decipher-make-checkpoint)
    (define-key map "N" 'decipher-adjacency-list)
    (define-key map "R" 'decipher-restore-checkpoint)
    (define-key map "U" 'decipher-undo)
    (define-key map " " 'decipher-keypress)
    (define-key map [remap undo] 'decipher-undo)
    (define-key map [remap advertised-undo] 'decipher-undo)
    (let ((key ?a))
      (while (<= key ?z)
	(define-key map (vector key) 'decipher-keypress)
	(cl-incf key)))
    map)
  "Keymap for Decipher mode.")


(defvar decipher-stats-mode-map
  (let ((map (make-keymap)))
    (suppress-keymap map)
    (define-key map "D" 'decipher-digram-list)
    (define-key map "F" 'decipher-frequency-count)
    (define-key map "N" 'decipher-adjacency-list)
    map)
"Keymap for Decipher-Stats mode.")


(defvar decipher-mode-syntax-table nil
  "Decipher mode syntax table")

(if decipher-mode-syntax-table
    ()
  (let ((table (make-syntax-table))
        (c ?0))
    (while (<= c ?9)
      (modify-syntax-entry c "_" table) ;Digits are not part of words
      (cl-incf c))
    (setq decipher-mode-syntax-table table)))

(defvar decipher-alphabet nil)
;; This is an alist containing entries (PLAIN-CHAR . CIPHER-CHAR),
;; where PLAIN-CHAR runs from ?a to ?z and CIPHER-CHAR is an uppercase
;; letter or space (which means no mapping is known for that letter).
;; This *must* contain entries for all lowercase characters.
(make-variable-buffer-local 'decipher-alphabet)

(defvar decipher-stats-buffer nil
  "The buffer which displays statistics for this ciphertext.
Do not access this variable directly, use the function
`decipher-stats-buffer' instead.")
(make-variable-buffer-local 'decipher-stats-buffer)

(defvar decipher-undo-list-size 0
  "The number of entries in the undo list.")
(make-variable-buffer-local 'decipher-undo-list-size)

(defvar decipher-undo-list nil
  "The undo list for this buffer.
Each element is either a cons cell (PLAIN-CHAR . CIPHER-CHAR) or a
list of such cons cells.")
(make-variable-buffer-local 'decipher-undo-list)

(defvar decipher-pending-undo-list nil)

;; The following variables are used by the analysis functions
;; and are defined here to avoid byte-compiler warnings.
;; Don't mess with them unless you know what you're doing.
(defvar decipher-char nil
  "See the functions decipher-loop-with-breaks and decipher-loop-no-breaks.")
(defvar decipher--prev-char)
(defvar decipher--digram)
(defvar decipher--digram-list)
(defvar decipher--before)
(defvar decipher--after)
(defvar decipher--freqs)

;;;===================================================================
;;; Code:
;;;===================================================================
;; Main entry points:
;;--------------------------------------------------------------------

;;;###autoload
(defun decipher ()
  "Format a buffer of ciphertext for cryptanalysis and enter Decipher mode."
  (interactive)
  ;; Make sure the buffer ends in a newline:
  (goto-char (point-max))
  (or (bolp)
      (insert "\n"))
  ;; See if it's already in decipher format:
  (goto-char (point-min))
  (if (looking-at "^(abcdefghijklmnopqrstuvwxyz   \
ABCDEFGHIJKLMNOPQRSTUVWXYZ   -\\*-decipher-\\*-\n)")
      (message "Buffer is already formatted, entering Decipher mode...")
    ;; Add the alphabet at the beginning of the file
    (insert "(abcdefghijklmnopqrstuvwxyz   \
ABCDEFGHIJKLMNOPQRSTUVWXYZ   -*-decipher-*-\n)\n\n")
    ;; Add lines for the solution:
    (let (begin)
      (while (not (eobp))
        (if (looking-at "^%")
            (forward-line)              ;Leave comments alone
          (delete-horizontal-space)
          (if (eolp)
              (forward-line)            ;Just leave blank lines alone
            (insert ":")                ;Mark ciphertext line
            (setq begin (point))
            (forward-line)
            (if decipher-force-uppercase
                (upcase-region begin (point))) ;Convert ciphertext to uppercase
            (insert ">\n")))))          ;Mark plaintext line
    (delete-blank-lines)                ;Remove any blank lines
    (delete-blank-lines))               ; at end of buffer
  (goto-char (point-min))
  (forward-line 3)
  (decipher-mode))

;;;###autoload
(defun decipher-mode ()
  "Major mode for decrypting monoalphabetic substitution ciphers.
Lower-case letters enter plaintext.
Upper-case letters are commands.

The buffer is made read-only so that normal Emacs commands cannot
modify it.

The most useful commands are:
\\<decipher-mode-map>
\\[decipher-digram-list]  Display a list of all digrams & their frequency
\\[decipher-frequency-count]  Display the frequency of each ciphertext letter
\\[decipher-adjacency-list]\
  Show adjacency list for current letter (lists letters appearing next to it)
\\[decipher-make-checkpoint]  Save the current cipher alphabet (checkpoint)
\\[decipher-restore-checkpoint]  Restore a saved cipher alphabet (checkpoint)"
  (interactive)
  (kill-all-local-variables)
  (setq buffer-undo-list  t             ;Disable undo
        indent-tabs-mode  nil           ;Do not use tab characters
        major-mode       'decipher-mode
        mode-name        "Decipher")
  (if decipher-force-uppercase
      (setq case-fold-search nil))      ;Case is significant when searching
  (use-local-map decipher-mode-map)
  (set-syntax-table decipher-mode-syntax-table)
  (unless (= (point-min) (point-max))
    (decipher-read-alphabet))
  (set (make-local-variable 'font-lock-defaults)
       '(decipher-font-lock-keywords t))
  ;; Make the buffer writable when we exit Decipher mode:
  (add-hook 'change-major-mode-hook
            (lambda () (setq buffer-read-only nil
                             buffer-undo-list nil))
            nil t)
  (run-mode-hooks 'decipher-mode-hook)
  (setq buffer-read-only t))
(put 'decipher-mode 'mode-class 'special)

;;--------------------------------------------------------------------
;; Normal key handling:
;;--------------------------------------------------------------------

(defmacro decipher-last-command-char ()
  ;; Return the char which ran this command (for compatibility with XEmacs)
  (if (fboundp 'event-to-character)
      '(event-to-character last-command-event)
    'last-command-event))

(defun decipher-keypress ()
  "Enter a plaintext or ciphertext character."
  (interactive)
  (let ((decipher-function 'decipher-set-map)
        buffer-read-only)               ;Make buffer writable
    (save-excursion
      (or (save-excursion
            (beginning-of-line)
            (let ((first-char (following-char)))
              (cond
               ((= ?: first-char)
                t)
               ((= ?> first-char)
                nil)
               ((= ?\( first-char)
                (setq decipher-function 'decipher-alphabet-keypress)
                t)
               ((= ?\) first-char)
                (setq decipher-function 'decipher-alphabet-keypress)
                nil)
               (t
                (error "Bad location")))))
          (let (goal-column)
            (forward-line -1)))
      (let ((char-a (following-char))
            (char-b (decipher-last-command-char)))
        (or (and (not (= ?w (char-syntax char-a)))
                 (= char-b ?\s)) ;Spacebar just advances on non-letters
            (funcall decipher-function char-a char-b)))))
  (forward-char))

(defun decipher-alphabet-keypress (a b)
  ;; Handle keypresses in the alphabet lines.
  ;; A is the character in the alphabet row (which starts with '(')
  ;; B is the character pressed
  (cond ((and (>= a ?A) (<= a ?Z))
         ;; If A is uppercase, then it is in the ciphertext alphabet:
         (decipher-set-map a b))
        ((and (>= a ?a) (<= a ?z))
         ;; If A is lowercase, then it is in the plaintext alphabet:
         (if (= b ?\s)
             ;; We are clearing the association (if any):
             (if (/= ?\s (setq b (cdr (assoc a decipher-alphabet))))
                 (decipher-set-map b ?\s))
           ;; Associate the plaintext char with the char pressed:
           (decipher-set-map b a)))
        (t
         ;; If A is not a letter, that's a problem:
         (error "Bad character"))))

;;--------------------------------------------------------------------
;; Undo:
;;--------------------------------------------------------------------

(defun decipher-undo ()
  "Undo a change in Decipher mode."
  (interactive)
  ;; If we don't get all the way thru, make last-command indicate that
  ;; for the following command.
  (setq this-command t)
  (or (eq major-mode 'decipher-mode)
      (error "This buffer is not in Decipher mode"))
  (or (eq last-command 'decipher-undo)
      (setq decipher-pending-undo-list decipher-undo-list))
  (or decipher-pending-undo-list
      (error "No further undo information"))
  (let ((undo-rec (pop decipher-pending-undo-list))
        buffer-read-only                ;Make buffer writable
        redo-map redo-rec undo-map)
    (or (consp (car undo-rec))
        (setq undo-rec (list undo-rec)))
    (while (setq undo-map (pop undo-rec))
      (setq redo-map (decipher-get-undo (cdr undo-map) (car undo-map)))
      (if redo-map
          (setq redo-rec
                (if (consp (car redo-map))
                    (append redo-map redo-rec)
                  (cons redo-map redo-rec))))
      (decipher-set-map (cdr undo-map) (car undo-map) t))
    (decipher-add-undo redo-rec))
  (setq this-command 'decipher-undo)
  (message "Undo!"))

(defun decipher-add-undo (undo-rec)
  "Add UNDO-REC to the undo list."
  (if undo-rec
      (progn
        (push undo-rec decipher-undo-list)
        (cl-incf decipher-undo-list-size)
        (if (> decipher-undo-list-size decipher-undo-limit)
            (let ((new-size (- decipher-undo-limit 100)))
              ;; Truncate undo list to NEW-SIZE elements:
              (setcdr (nthcdr (1- new-size) decipher-undo-list) nil)
              (setq decipher-undo-list-size new-size))))))

(defun decipher-copy-cons (cons)
  (if cons
      (cons (car cons) (cdr cons))))

(defun decipher-get-undo (cipher-char plain-char)
  ;; Return an undo record that will undo the result of
  ;;   (decipher-set-map CIPHER-CHAR PLAIN-CHAR)
  ;; We must copy the cons cell because the original cons cells will be
  ;; modified using setcdr.
  (let ((cipher-map (decipher-copy-cons (rassoc cipher-char decipher-alphabet)))
        (plain-map  (decipher-copy-cons (assoc  plain-char  decipher-alphabet))))
    (cond ((equal ?\s plain-char)
           cipher-map)
          ((equal cipher-char (cdr plain-map))
           nil)                         ;We aren't changing anything
          ((equal ?\s (cdr plain-map))
           (or cipher-map (cons ?\s cipher-char)))
          (cipher-map
           (list plain-map cipher-map))
          (t
           plain-map))))

;;--------------------------------------------------------------------
;; Mapping ciphertext and plaintext:
;;--------------------------------------------------------------------

(defun decipher-set-map (cipher-char plain-char &optional no-undo)
  ;; Associate a ciphertext letter with a plaintext letter
  ;; CIPHER-CHAR must be an uppercase or lowercase letter
  ;; PLAIN-CHAR must be a lowercase letter (or a space)
  ;; NO-UNDO if non-nil means do not record undo information
  ;; Any existing associations for CIPHER-CHAR or PLAIN-CHAR will be erased.
  (setq cipher-char (upcase cipher-char))
  (or (and (>= cipher-char ?A) (<= cipher-char ?Z))
      (error "Bad character"))          ;Cipher char must be uppercase letter
  (or no-undo
      (decipher-add-undo (decipher-get-undo cipher-char plain-char)))
  (let ((cipher-string (char-to-string cipher-char))
        (plain-string  (char-to-string plain-char))
        case-fold-search                ;Case is significant
        mapping bound)
    (save-excursion
      (goto-char (point-min))
      (if (setq mapping (rassoc cipher-char decipher-alphabet))
          (progn
            (setcdr mapping ?\s)
            (search-forward-regexp (concat "^([a-z]*"
                                           (char-to-string (car mapping))))
            (decipher-insert ?\s)
            (beginning-of-line)))
      (if (setq mapping (assoc plain-char decipher-alphabet))
          (progn
            (if (/= ?\s (cdr mapping))
                (decipher-set-map (cdr mapping) ?\s t))
            (setcdr mapping cipher-char)
            (search-forward-regexp (concat "^([a-z]*" plain-string))
            (decipher-insert cipher-char)
            (beginning-of-line)))
      (search-forward-regexp (concat "^([a-z]+   [A-Z]*" cipher-string))
      (decipher-insert plain-char)
      (setq case-fold-search t          ;Case is not significant
            cipher-string    (downcase cipher-string))
      (let ((font-lock-fontify-region-function 'ignore))
        ;; insert-and-inherit will pick the right face automatically
        (while (search-forward-regexp "^:" nil t)
          (setq bound (point-at-eol))
          (while (search-forward cipher-string bound 'end)
            (decipher-insert plain-char)))))))

(defun decipher-insert (char)
  ;; Insert CHAR in the row below point.  It replaces any existing
  ;; character in that position.
  (let ((col (1- (current-column))))
    (save-excursion
      (forward-line)
      (or (= ?\> (following-char))
          (= ?\) (following-char))
          (error "Bad location"))
      (move-to-column col t)
      (or (eolp)
          (delete-char 1))
      (insert-and-inherit char))))

;;--------------------------------------------------------------------
;; Checkpoints:
;;--------------------------------------------------------------------
;; A checkpoint is a comment of the form:
;;   %!ABCDEFGHIJKLMNOPQRSTUVWXYZ! Description
;; Such comments are usually placed at the end of the buffer following
;; this header (which is inserted by decipher-make-checkpoint):
;;   %---------------------------
;;   % Checkpoints:
;;   % abcdefghijklmnopqrstuvwxyz
;; but this is not required; checkpoints can be placed anywhere.
;;
;; The description is optional; all that is required is the alphabet.

(defun decipher-make-checkpoint (desc)
  "Checkpoint the current cipher alphabet.
This records the current alphabet so you can return to it later.
You may have any number of checkpoints.
Type `\\[decipher-restore-checkpoint]' to restore a checkpoint."
  (interactive "sCheckpoint description: ")
  (or (stringp desc)
      (setq desc ""))
  (let (alphabet
        buffer-read-only)               ;Make buffer writable
    (goto-char (point-min))
    (re-search-forward "^)")
    (move-to-column 27 t)
    (setq alphabet (buffer-substring-no-properties (- (point) 26) (point)))
    (if (re-search-forward "^%![A-Z ]+!" nil 'end)
       nil ; Add new checkpoint with others
      (if (re-search-backward "^% *Local Variables:" nil t)
          ;; Add checkpoints before local variables list:
          (progn (forward-line -1)
                 (or (looking-at "^ *$")
                     (progn (forward-line) (insert ?\n) (forward-line -1)))))
      (insert "\n%" (make-string 69 ?\-)
              "\n% Checkpoints:\n% abcdefghijklmnopqrstuvwxyz\n"))
    (beginning-of-line)
    (insert "%!" alphabet "! " desc ?\n)))

(defun decipher-restore-checkpoint ()
  "Restore the cipher alphabet from a checkpoint.
If point is not on a checkpoint line, moves to the first checkpoint line.
If point is on a checkpoint, restores that checkpoint.

Type `\\[decipher-make-checkpoint]' to make a checkpoint."
  (interactive)
  (beginning-of-line)
  (if (looking-at "%!\\([A-Z ]+\\)!")
      ;; Restore this checkpoint:
      (let ((alphabet (match-string 1))
            buffer-read-only)           ;Make buffer writable
        (goto-char (point-min))
        (re-search-forward "^)")
        (or (eolp)
            (delete-region (point) (progn (end-of-line) (point))))
        (insert alphabet)
        (decipher-resync))
    ;; Move to the first checkpoint:
    (goto-char (point-min))
    (if (re-search-forward "^%![A-Z ]+!" nil t)
        (message "Select the checkpoint to restore and type `%s'"
                 (substitute-command-keys "\\[decipher-restore-checkpoint]"))
      (error "No checkpoints in this buffer"))))

;;--------------------------------------------------------------------
;; Miscellaneous commands:
;;--------------------------------------------------------------------

(defun decipher-complete-alphabet ()
  "Complete the cipher alphabet.
This fills any blanks in the cipher alphabet with the unused letters
in alphabetical order.  Use this when you have a keyword cipher and
you have determined the keyword."
  (interactive)
  (let ((cipher-char ?A)
        (ptr decipher-alphabet)
        buffer-read-only                ;Make buffer writable
        plain-map undo-rec)
    (while (setq plain-map (pop ptr))
      (if (equal ?\s (cdr plain-map))
          (progn
            (while (rassoc cipher-char decipher-alphabet)
              ;; Find the next unused letter
              (cl-incf cipher-char))
            (push (cons ?\s cipher-char) undo-rec)
            (decipher-set-map cipher-char (car plain-map) t))))
    (decipher-add-undo undo-rec)))

(defun decipher-show-alphabet ()
  "Display the current cipher alphabet in the message line."
  (interactive)
  (message "%s"
   (mapconcat (lambda (a)
                (concat
                 (char-to-string (car a))
                 (char-to-string (cdr a))))
              decipher-alphabet
              "")))

(defun decipher-resync ()
  "Reprocess the buffer using the alphabet from the top.
This regenerates all deciphered plaintext and clears the undo list.
You should use this if you edit the ciphertext."
  (interactive)
  (message "Reprocessing buffer...")
  (let (alphabet
        buffer-read-only                ;Make buffer writable
        mapping)
    (save-excursion
      (decipher-read-alphabet)
      (setq alphabet decipher-alphabet)
      (goto-char (point-min))
      (and (re-search-forward "^).+" nil t)
           (replace-match ")" nil nil))
      (while (re-search-forward "^>.+" nil t)
        (replace-match ">" nil nil))
      (decipher-read-alphabet)
      (while (setq mapping (pop alphabet))
        (or (equal ?\s (cdr mapping))
            (decipher-set-map (cdr mapping) (car mapping))))))
  (setq decipher-undo-list       nil
        decipher-undo-list-size  0)
  (message "Reprocessing buffer...done"))

;;--------------------------------------------------------------------
;; Miscellaneous functions:
;;--------------------------------------------------------------------

(defun decipher-read-alphabet ()
  "Build the decipher-alphabet from the alphabet line in the buffer."
  (save-excursion
    (goto-char (point-min))
    (search-forward-regexp "^)")
    (move-to-column 27 t)
    (setq decipher-alphabet nil)
    (let ((plain-char ?z))
      (while (>= plain-char ?a)
        (backward-char)
        (push (cons plain-char (following-char)) decipher-alphabet)
        (cl-decf plain-char)))))

;;;===================================================================
;;; Analyzing ciphertext:
;;;===================================================================

(defun decipher-frequency-count ()
  "Display the frequency count in the statistics buffer."
  (interactive)
  (decipher-analyze)
  (decipher-display-regexp "^A" "^[A-Z][A-Z]"))

(defun decipher-digram-list ()
  "Display the list of digrams in the statistics buffer."
  (interactive)
  (decipher-analyze)
  (decipher-display-regexp "[A-Z][A-Z] +[0-9]" "^$"))

(defun decipher-adjacency-list (cipher-char)
  "Display the adjacency list for the letter at point.
The adjacency list shows all letters which come next to CIPHER-CHAR.

An adjacency list (for the letter X) looks like this:
       1 1         1     1   1       3 2 1             3   8
X: 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 *  11   14   9%
     1 1                 1       2   1   1     2       5   7
This says that X comes before D once, and after B once.  X begins 5
words, and ends 3 words (`*' represents a space).  X comes before 8
different letters, after 7 different letters, and is next to a total
of 11 different letters.  It occurs 14 times, making up 9% of the
ciphertext."
  (interactive (list (upcase (following-char))))
  (decipher-analyze)
  (let (start end)
    (with-current-buffer (decipher-stats-buffer)
      (goto-char (point-min))
      (or (re-search-forward (format "^%c: " cipher-char) nil t)
          (error "Character `%c' is not used in ciphertext" cipher-char))
      (forward-line -1)
      (setq start (point))
      (forward-line 3)
      (setq end (point)))
    (decipher-display-range start end)))

;;--------------------------------------------------------------------
(defun decipher-analyze ()
  "Perform frequency analysis on the current buffer if necessary."
  (cond
   ;; If this is the statistics buffer, do nothing:
   ((eq major-mode 'decipher-stats-mode))
   ;; If this is the Decipher buffer, see if the stats buffer exists:
   ((eq major-mode 'decipher-mode)
    (or (and (bufferp decipher-stats-buffer)
             (buffer-name decipher-stats-buffer))
        (decipher-analyze-buffer)))
   ;; Otherwise:
   (t (error "This buffer is not in Decipher mode"))))

;;--------------------------------------------------------------------
(defun decipher-display-range (start end)
  "Display text between START and END in the statistics buffer.
START and END are positions in the statistics buffer.  Makes the
statistics buffer visible and sizes the window to just fit the
displayed text, but leaves the current window selected."
  (let ((stats-buffer (decipher-stats-buffer))
        (current-window (selected-window))
        (pop-up-windows t))
    (or (eq (current-buffer) stats-buffer)
        (pop-to-buffer stats-buffer))
    (goto-char start)
    (or (one-window-p t)
        (enlarge-window (- (1+ (count-lines start end)) (window-height))))
    (recenter 0)
    (select-window current-window)))

(defun decipher-display-regexp (start-regexp end-regexp)
  "Display text between two regexps in the statistics buffer.

START-REGEXP matches the first line to display.
END-REGEXP matches the line after that which ends the display.
The ending line is included in the display unless it is blank."
  (let (start end)
    (with-current-buffer (decipher-stats-buffer)
      (goto-char (point-min))
      (re-search-forward start-regexp)
      (beginning-of-line)
      (setq start (point))
      (re-search-forward end-regexp)
      (beginning-of-line)
      (or (looking-at "^ *$")
          (forward-line 1))
      (setq end (point)))
    (decipher-display-range start end)))

;;--------------------------------------------------------------------
(defun decipher-loop-with-breaks (func)
  "Loop through ciphertext, calling FUNC once for each letter & word division.

FUNC is called with no arguments, and its return value is unimportant.
It may examine `decipher-char' to see the current ciphertext
character.  `decipher-char' contains either an uppercase letter or a space.

FUNC is called exactly once between words, with `decipher-char' set to
a space.

See `decipher-loop-no-breaks' if you do not care about word divisions."
  (let ((decipher-char ?\s)
        (decipher--loop-prev-char ?\s))
    (save-excursion
      (goto-char (point-min))
      (funcall func)              ;Space marks beginning of first word
      (while (search-forward-regexp "^:" nil t)
        (while (not (eolp))
          (setq decipher-char (upcase (following-char)))
          (or (and (>= decipher-char ?A) (<= decipher-char ?Z))
              (setq decipher-char ?\s))
          (or (and (equal decipher-char ?\s)
                   (equal decipher--loop-prev-char ?\s))
              (funcall func))
          (setq decipher--loop-prev-char decipher-char)
          (forward-char))
        (or (equal decipher-char ?\s)
            (progn
              (setq decipher-char ?\s
                    decipher--loop-prev-char ?\s)
              (funcall func)))))))

(defun decipher-loop-no-breaks (func)
  "Loop through ciphertext, calling FUNC once for each letter.

FUNC is called with no arguments, and its return value is unimportant.
It may examine `decipher-char' to see the current ciphertext letter.
`decipher-char' contains an uppercase letter.

Punctuation and spacing in the ciphertext are ignored.
See `decipher-loop-with-breaks' if you care about word divisions."
  (let (decipher-char)
    (save-excursion
      (goto-char (point-min))
      (while (search-forward-regexp "^:" nil t)
        (while (not (eolp))
          (setq decipher-char (upcase (following-char)))
          (and (>= decipher-char ?A)
               (<= decipher-char ?Z)
               (funcall func))
          (forward-char))))))

;;--------------------------------------------------------------------
;; Perform the analysis:
;;--------------------------------------------------------------------

(defun decipher-insert-frequency-counts (freq-list total)
  "Insert frequency counts in current buffer.
Each element of FREQ-LIST is a list (LETTER FREQ ...).
TOTAL is the total number of letters in the ciphertext."
  (let ((i 4) temp-list)
    (while (> i 0)
      (setq temp-list freq-list)
      (while temp-list
        (insert (caar temp-list)
                (format "%4d%3d%%  "
                        (cl-cadar temp-list)
                        (/ (* 100 (cl-cadar temp-list)) total)))
        (setq temp-list (nthcdr 4 temp-list)))
      (insert ?\n)
      (setq freq-list (cdr freq-list)
            i         (1- i)))))

(defun decipher--analyze ()
  ;; Perform frequency analysis on ciphertext.
  ;;
  ;; This function is called repeatedly with decipher-char set to each
  ;; character of ciphertext.  It uses decipher--prev-char to remember
  ;; the previous ciphertext character.
  ;;
  ;; It builds several data structures, which must be initialized
  ;; before the first call to decipher--analyze.  The arrays are
  ;; indexed with A = 0, B = 1, ..., Z = 25, SPC = 26 (if used).
  ;;   decipher--after: (initialize to zeros)
  ;;     A vector of 26 vectors of 27 integers.  The first vector
  ;;     represents the number of times A follows each character, the
  ;;     second vector represents B, and so on.
  ;;   decipher--before: (initialize to zeros)
  ;;     The same as decipher--after, but representing the number of
  ;;     times the character precedes each other character.
  ;;   decipher--digram-list: (initialize to nil)
  ;;     An alist with an entry for each digram (2-character sequence)
  ;;     encountered.  Each element is a cons cell (DIGRAM . FREQ),
  ;;     where DIGRAM is a 2 character string and FREQ is the number
  ;;     of times it occurs.
  ;;   decipher--freqs: (initialize to zeros)
  ;;     A vector of 26 integers, counting the number of occurrences
  ;;     of the corresponding characters.
  (setq decipher--digram (format "%c%c" decipher--prev-char decipher-char))
  (cl-incf (cdr (or (assoc decipher--digram decipher--digram-list)
                 (car (push (cons decipher--digram 0)
                            decipher--digram-list)))))
  (and (>= decipher--prev-char ?A)
       (cl-incf (aref (aref decipher--before (- decipher--prev-char ?A))
                   (if (equal decipher-char ?\s)
                       26
                     (- decipher-char ?A)))))
  (and (>= decipher-char ?A)
       (cl-incf (aref decipher--freqs (- decipher-char ?A)))
       (cl-incf (aref (aref decipher--after (- decipher-char ?A))
                   (if (equal decipher--prev-char ?\s)
                       26
                     (- decipher--prev-char ?A)))))
  (setq decipher--prev-char decipher-char))

(defun decipher--digram-counts (counts)
  "Generate the counts for an adjacency list."
  (let ((total 0))
    (concat
     (mapconcat (lambda (x)
                  (cond ((> x 99) (cl-incf total) "XX")
                        ((> x 0)  (cl-incf total) (format "%2d" x))
                        (t        "  ")))
                counts
                "")
     (format "%4d" (if (> (aref counts 26) 0)
                       (1- total)    ;Don't count space
                     total)))))

(defun decipher--digram-total (before-count after-count)
  "Count the number of different letters a letter appears next to."
  ;; We do not include spaces (word divisions) in this count.
  (let ((total 0)
        (i 26))
    (while (>= (cl-decf i) 0)
      (if (or (> (aref before-count i) 0)
              (> (aref after-count  i) 0))
          (cl-incf total)))
    total))

(defun decipher-analyze-buffer ()
  "Perform frequency analysis and store results in statistics buffer.
Creates the statistics buffer if it doesn't exist."
  (let ((decipher--prev-char (if decipher-ignore-spaces ?\s ?\*))
        (decipher--before (make-vector 26 nil))
        (decipher--after  (make-vector 26 nil))
        (decipher--freqs   (make-vector 26 0))
        (total-chars  0)
        decipher--digram decipher--digram-list freq-list)
    (message "Scanning buffer...")
    (let ((i 26))
      (while (>= (cl-decf i) 0)
        (aset decipher--before i (make-vector 27 0))
        (aset decipher--after  i (make-vector 27 0))))
    (if decipher-ignore-spaces
        (progn
          (decipher-loop-no-breaks 'decipher--analyze)
          ;; The first character of ciphertext was marked as following a space:
          (let ((i 26))
            (while (>= (cl-decf i) 0)
              (aset (aref decipher--after  i) 26 0))))
      (decipher-loop-with-breaks 'decipher--analyze))
    (message "Processing results...")
    (setcdr (last decipher--digram-list 2) nil)   ;Delete the phony "* " digram
    ;; Sort the digram list by frequency and alphabetical order:
    (setq decipher--digram-list (sort (sort decipher--digram-list
                                  (lambda (a b) (string< (car a) (car b))))
                            (lambda (a b) (> (cdr a) (cdr b)))))
    ;; Generate the frequency list:
    ;;   Each element is a list of 3 elements (LETTER FREQ DIFFERENT),
    ;;   where LETTER is the ciphertext character, FREQ is the number
    ;;   of times it occurs, and DIFFERENT is the number of different
    ;;   letters it appears next to.
    (let ((i 26))
      (while (>= (cl-decf i) 0)
        (setq freq-list
              (cons (list (+ i ?A)
                          (aref decipher--freqs i)
                          (decipher--digram-total (aref decipher--before i)
                                                  (aref decipher--after  i)))
                    freq-list)
              total-chars (+ total-chars (aref decipher--freqs i)))))
    ;; Switch to statistics buffer, creating it if necessary:
    (with-current-buffer (decipher-stats-buffer t)
      ;; This can't happen, but it never hurts to double-check:
      (or (eq major-mode 'decipher-stats-mode)
          (error "Buffer %s is not in Decipher-Stats mode" (buffer-name)))
      (setq buffer-read-only nil)
      (erase-buffer)
      ;; Display frequency counts for letters A-Z:
      (decipher-insert-frequency-counts freq-list total-chars)
      (insert ?\n)
      ;; Display frequency counts for letters in order of frequency:
      (setq freq-list (sort freq-list
                            (lambda (a b) (> (cl-second a) (cl-second b)))))
      (decipher-insert-frequency-counts freq-list total-chars)
      ;; Display letters in order of frequency:
      (insert ?\n (mapconcat (lambda (a) (char-to-string (car a)))
                             freq-list nil)
              "\n\n")
      ;; Display list of digrams in order of frequency:
      (let* ((rows (floor (+ (length decipher--digram-list) 9) 10))
             (i rows)
             temp-list)
        (while (> i 0)
          (setq temp-list decipher--digram-list)
          (while temp-list
            (insert (caar temp-list)
                    (format "%3d   "
                            (cdar temp-list)))
            (setq temp-list (nthcdr rows temp-list)))
          (delete-horizontal-space)
          (insert ?\n)
          (setq decipher--digram-list (cdr decipher--digram-list)
                i           (1- i))))
      ;; Display adjacency list for each letter, sorted in descending
      ;; order of the number of adjacent letters:
      (setq freq-list (sort freq-list
                            (lambda (a b) (> (cl-third a) (cl-third b)))))
      (let ((temp-list freq-list)
            entry i)
        (while (setq entry (pop temp-list))
          (if (equal 0 (cl-second entry))
              nil                       ;This letter was not used
            (setq i (- (car entry) ?A))
            (insert ?\n "  "
                    (decipher--digram-counts (aref decipher--before i)) ?\n
                    (car entry)
                    ": 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 *"
                    (format "%4d %4d %3d%%\n  "
                            (cl-third entry) (cl-second entry)
                            (/ (* 100 (cl-second entry)) total-chars))
                    (decipher--digram-counts (aref decipher--after  i)) ?\n))))
      (setq buffer-read-only t)
      (set-buffer-modified-p nil)
      ))
  (message nil))

;;====================================================================
;; Statistics Buffer:
;;====================================================================

(defun decipher-stats-mode ()
  "Major mode for displaying ciphertext statistics."
  (interactive)
  (kill-all-local-variables)
  (setq buffer-read-only  t
        buffer-undo-list  t             ;Disable undo
        case-fold-search  nil           ;Case is significant when searching
        indent-tabs-mode  nil           ;Do not use tab characters
        major-mode       'decipher-stats-mode
        mode-name        "Decipher-Stats")
  (use-local-map decipher-stats-mode-map)
  (run-mode-hooks 'decipher-stats-mode-hook))
(put 'decipher-stats-mode 'mode-class 'special)

;;--------------------------------------------------------------------

(defun decipher-display-stats-buffer ()
  "Make the statistics buffer visible, but do not select it."
  (let ((stats-buffer (decipher-stats-buffer))
        (current-window (selected-window)))
    (or (eq (current-buffer) stats-buffer)
        (progn
          (pop-to-buffer stats-buffer)
          (select-window current-window)))))

(defun decipher-stats-buffer (&optional create)
  "Return the buffer used for decipher statistics.
If CREATE is non-nil, create the buffer if it doesn't exist.
This is guaranteed to return a buffer in Decipher-Stats mode;
if it can't, it signals an error."
  (cond
   ;; We may already be in the statistics buffer:
   ((eq major-mode 'decipher-stats-mode)
    (current-buffer))
   ;; See if decipher-stats-buffer exists:
   ((and (bufferp decipher-stats-buffer)
         (buffer-name decipher-stats-buffer))
    (or (with-current-buffer decipher-stats-buffer
          (eq major-mode 'decipher-stats-mode))
        (error "Buffer %s is not in Decipher-Stats mode"
               (buffer-name decipher-stats-buffer)))
    decipher-stats-buffer)
   ;; Create a new buffer if requested:
   (create
    (let ((stats-name (concat "*" (buffer-name) "*")))
      (setq decipher-stats-buffer
            (if (eq 'decipher-stats-mode
                    (cdr-safe (assoc 'major-mode
                                     (buffer-local-variables
                                      (get-buffer stats-name)))))
                ;; We just lost track of the statistics buffer:
                (get-buffer stats-name)
              (generate-new-buffer stats-name))))
    (with-current-buffer decipher-stats-buffer
      (decipher-stats-mode))
    decipher-stats-buffer)
   ;; Give up:
   (t (error "No statistics buffer"))))

;;====================================================================

(provide 'decipher)

;;(defun decipher-show-undo-list ()
;;  "Display the undo list (for debugging purposes)."
;;  (interactive)
;;  (with-output-to-temp-buffer "*Decipher Undo*"
;;    (let ((undo-list decipher-undo-list)
;;          undo-rec undo-map)
;;      (with-current-buffer "*Decipher Undo*"
;;        (while (setq undo-rec (pop undo-list))
;;          (or (consp (car undo-rec))
;;              (setq undo-rec (list undo-rec)))
;;          (insert ?\()
;;          (while (setq undo-map (pop undo-rec))
;;            (insert (cdr undo-map) (car undo-map) ?\s))
;;          (delete-char -1)
;;          (insert ")\n"))))))

;;; decipher.el ends here