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Groups > comp.lang.forth > #58912

Rosetta: Caesar cipher

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> Implement a Caesar cipher, both encoding and decoding. 
> The key is an integer from 1 to 25. 
> 
> This cipher rotates (either towards left or right) the letters
> of the alphabet (A to Z).
> 
> The encoding replaces each letter with the 1st to 25th next
> letter in the alphabet (wrapping Z to A).
> 
> So key 2 encrypts "HI" to "JK", but key 20 encrypts "HI" to "BC".


(use srfi-13)

(define lower-alphabet
  (string-tabulate
    (lambda(i) (integer->char (+ (char->integer #\a) i))) 26))

(define (shifted-alphabet n)
  ;; Rotate the lowercase letters.
  (define s (xsubstring lower-alphabet n))
  (string-append s (string-upcase s)))

(define (encipher n str)
  (string-translate str
    (shifted-alphabet 0)
    (shifted-alphabet n)))
 
(define (decipher n str) (encipher (- n) str))


(encipher 3 "However, the man wasn't there.[9]")
 ===>
"Krzhyhu, wkh pdq zdvq'w wkhuh.[9]"

(decipher 3 (encipher 3 "However, the man wasn't there.[9]"))
 ===>
"However, the man wasn't there.[9]"


In Forth?


-- 
[W]e had enough employees who made more than 85 to fill all the openings.  The
highest score that any of the blacks scored on the test was 11.  The lowest
score that any black made on the test was 4.  All four of those blacks went
into skilled-trades training.
https://archive.org/download/TheOldmanArchives/oldman29-081003.mp3

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Rosetta: Caesar cipher "Robert L." <No_spamming@noWhere_7073.org> - 2017-05-09 20:47 +0000
  Re: Rosetta: Caesar cipher Joel Rees <joel.rees@gmail.com> - 2017-05-09 20:20 -0700
    Re: Rosetta: Caesar cipher hughaguilar96@gmail.com - 2017-05-12 13:52 -0700
  Re: Rosetta: Caesar cipher rickman <gnuarm@gmail.com> - 2017-05-10 20:07 -0400
    Re: Rosetta: Caesar cipher Julian Fondren <julian.fondren@gmail.com> - 2017-05-10 21:12 -0700
      Re: Rosetta: Caesar cipher rickman <gnuarm@gmail.com> - 2017-05-11 01:50 -0400
        Re: Rosetta: Caesar cipher Julian Fondren <julian.fondren@gmail.com> - 2017-05-11 05:34 -0700
          Re: Rosetta: Caesar cipher Alex <alex@rivadpm.com> - 2017-05-11 14:39 +0100
            Re: Rosetta: Caesar cipher anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2017-05-11 16:04 +0000
              Re: Rosetta: Caesar cipher Alex <alex@rivadpm.com> - 2017-05-11 21:35 +0100
            Re: Rosetta: Caesar cipher mhx@iae.nl - 2017-05-11 10:21 -0700
          Re: Rosetta: Caesar cipher rickman <gnuarm@gmail.com> - 2017-05-12 13:41 -0400

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