```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 ``` ```; diana cryptosystem (define rand #f) (define randint #f) (let ((two31 #x80000000) (a (make-vector 56 -1)) (fptr #f)) (define (mod-diff x y) (modulo (- x y) two31)) ; generic version ; (define (mod-diff x y) (logand (- x y) #x7FFFFFFF)) ; fast version (define (flip-cycle) (do ((ii 1 (+ ii 1)) (jj 32 (+ jj 1))) ((< 55 jj)) (vector-set! a ii (mod-diff (vector-ref a ii) (vector-ref a jj)))) (do ((ii 25 (+ ii 1)) (jj 1 (+ jj 1))) ((< 55 ii)) (vector-set! a ii (mod-diff (vector-ref a ii) (vector-ref a jj)))) (set! fptr 54) (vector-ref a 55)) (define (init-rand seed) (let* ((seed (mod-diff seed 0)) (prev seed) (next 1)) (vector-set! a 55 prev) (do ((i 21 (modulo (+ i 21) 55))) ((zero? i)) (vector-set! a i next) (set! next (mod-diff prev next)) (set! seed (+ (quotient seed 2) (if (odd? seed) #x40000000 0))) (set! next (mod-diff next seed)) (set! prev (vector-ref a i))) (flip-cycle) (flip-cycle) (flip-cycle) (flip-cycle) (flip-cycle))) (define (next-rand) (if (negative? (vector-ref a fptr)) (flip-cycle) (let ((next (vector-ref a fptr))) (set! fptr (- fptr 1)) next))) (define (unif-rand m) (let ((t (- two31 (modulo two31 m)))) (let loop ((r (next-rand))) (if (<= t r) (loop (next-rand)) (modulo r m))))) (init-rand 19380110) ; happy birthday donald e knuth (set! rand (lambda seed (cond ((null? seed) (/ (next-rand) two31)) ((eq? (car seed) 'get) (cons fptr (vector->list a))) ((eq? (car seed) 'set) (set! fptr (caadr seed)) (set! a (list->vector (cdadr seed)))) (else (/ (init-rand (modulo (numerator (inexact->exact (car seed))) two31)) two31))))) (set! randint (lambda args (cond ((null? (cdr args)) (if (< (car args) two31) (unif-rand (car args)) (floor (* (next-rand) (car args))))) ((< (car args) (cadr args)) (let ((span (- (cadr args) (car args)))) (+ (car args) (if (< span two31) (unif-rand span) (floor (* (next-rand) span)))))) (else (let ((span (- (car args) (cadr args)))) (- (car args) (if (< span two31) (unif-rand span) (floor (* (next-rand) span)))))))))) (define random-integer randint) ;; ;; Implement a version of One Time Pad encryption. ;; Use a trigraph / diana pad method ;; http://danmorgan76.wordpress.com/2013/09/30/encryption-via-a-one-time-pad/ ;; http://home.earthlink.net/~specforces/spdiana.htm ;; (define (a->i letter) (- (char->integer letter) 65)) (define (i->a index) (integer->char (+ 65 index))) (define (rand-char) (i->a (random-integer 26))) (define (range low high) (if (> low high) '() (cons low (range (+ 1 low) high)))) (define (head items) (let loop ((i 0) (items items) (accum '())) (cond ((or (null? items) (= i 5)) (reverse accum)) (else (loop (+ i 1) (cdr items) (cons (car items) accum)))))) (define (tail items) (reverse (head (reverse items)))) (define (make-pad rows cols) (define (make-block) (apply string (map (lambda (i) (rand-char)) (range 1 5)))) (define (make-row) (for-each (lambda (i) (if (> i 1) (display " ")) (display (make-block))) (range 1 cols))) (for-each (lambda (i) (make-row) (newline)) (range 1 rows))) (define (tri-row i) (reverse (map (lambda (pos) (i->a (modulo (- pos i) 26))) (range 0 25)))) (define (tri-lookup key plain) (let loop ((key (string->list key)) (plain (string->list plain)) (coded '())) (cond ((null? plain) (apply string (reverse coded))) ((equal? #\space (car plain)) (loop (cdr key) (cdr plain) (cons #\space coded))) (else (let ((row (a->i (car plain))) (col (a->i (car key)))) (loop (cdr key) (cdr plain) (cons (list-ref (tri-row row) col) coded))))))) (make-pad 4 4) (newline) (define k "ASDFA POUYK") (display (tri-lookup k "HELLO WORLD")) (newline) (display (tri-lookup k "SDLJL OXOQM")) (newline) ```
 ```1 2 3 4 5 6 7 ``` ```QNQWW BRBSQ GBNSR IZJKA ZRNQX SHEYI UQVTW AETTV EUNBP HSWAS OYSOH IDXRX SXBMN GXKQX HLTAM EBDRG SDLJL OXOQM HELLO WORLD ```