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Vigenère cipher: Difference between revisions
→{{header|CL}}
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Decrypted: BEWARETHEJABBERWOCKMYSONTHEJAWSTHATBITETHECLAWSTHATCATCH
</pre>
=={{header|Common Lisp}}==
This doesn't assume anything about character codes other than A-Z being a contiguous block (but still, we could be using EBCDIC. Who knows.)
<lang lisp>(defun strip (s)
(remove-if-not
(lambda (c) (char<= #\A c #\Z))
(string-upcase s)))
(defun vigenère (s key &key decipher
&aux (A (char-code #\A))
(op (if decipher #'- #'+)))
(labels
((to-char (c) (code-char (+ c A)))
(to-code (c) (- (char-code c) A)))
(let ((k (map 'list #'to-code (strip key))))
(setf (cdr (last k)) k)
(map 'string
(lambda (c)
(prog1
(to-char
(mod (funcall op (to-code c) (car k)) 26))
(setf k (cdr k))))
(strip s)))))
(let* ((msg "Beware the Jabberwock... The jaws that... the claws that catch!")
(key "vigenere cipher")
(enc (vigenère msg key))
(dec (vigenère enc key :decipher t)))
(format t "msg: ~a~%enc: ~a~%dec: ~a~%" msg enc dec))</lang>output<lang>msg: Beware the Jabberwock... The jaws that... the claws that catch!
enc: WMCEEIKLGRPIFVMEUGXXYILILZXYVBZLRGCEYAIOEKXIZGU
dec: BEWARETHEJABBERWOCKTHEJAWSTHATTHECLAWSTHATCATCH</lang>
=={{header|Clojure}}==
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