Vigenère cipher: Difference between revisions

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Updated version by [http://rosettacode.org/wiki/User:Vanyamil User:Vanyamil]

This is a custom, more functional version of the existing solution, due to

'''[https://caml.inria.fr/pub/docs/manual-ocaml/libref/String.html OCaml 4.05's unsafe-string compatibility mode]'''

{{works with|OCaml|4.05 or above}}

<lang OCaml>

(* Task : Vigenère_cipher *)

(* This is a custom, more functional version of an existing solution,

due to OCaml 4.05's unsafe-string compatibility mode:

https://caml.inria.fr/pub/docs/manual-ocaml/libref/String.html

*)

(*** Helpers ***)

(* Verbose type abbreviation *)

type key = string

(* Rotate a single uppercase letter *)

let ascii_caesar_shift : bool -> char -> char -> char =

let min_range = Char.code 'A' in

let max_range = Char.code 'Z' in

(* aka 26 but this code can be adapted to larger ranges, such as the ASCII printable range (codes 32 to 126). *)

let range_len = max_range - min_range + 1 in

let actual_fun (dir : bool) (c1 : char) (c2 : char) : char =

let n1 = Char.code c1 in

let n2 = Char.code c2 - min_range in

let sum = (if dir then (+) else (-)) n1 n2 in

( (* Effectively mod function, but simplified and works on negatives. *)

if sum > max_range

then sum - range_len

else if sum < min_range

then sum + range_len

else sum

) |> Char.chr

in

actual_fun

(* Remove non-letters and uppercase *)

let ascii_upper_letters_only (s : string) : string =

let slen = String.length s in

(* Make a list of escaped uppercase letter chars *)

let rec toLetterList sidx acc =

if sidx >= slen

then List.rev acc

else

let c = s.[sidx] in

if c >= 'A' && c <= 'Z'

then toLetterList (sidx + 1) ((c |> Char.escaped) :: acc)

else if c >= 'a' && c <= 'z'

then toLetterList (sidx + 1) ((c |> Char.uppercase_ascii |> Char.escaped) :: acc)

else toLetterList (sidx + 1) acc

in

toLetterList 0 [] |> String.concat ""

(*** Actual task at hand ***)

let vig_crypt (dir : bool) (key : key) (message : string) : string =

let message = ascii_upper_letters_only message in

let key = ascii_upper_letters_only key in

let klen = String.length key in

let aux idx c =

let kidx = idx mod klen in

let e = ascii_caesar_shift dir c key.[kidx] in

e

in

String.mapi aux message

let encrypt : key -> string -> string = vig_crypt true

let decrypt : key -> string -> string = vig_crypt false

(*** Output ***)

let () =

let str = "Beware the Jabberwock, my son! The jaws that bite, \

the claws that catch!" in

let key = "VIGENERECIPHER" in

let ct = encrypt key str in

let pt = decrypt key ct in

Printf.printf "Text: %s\n" str;

Printf.printf "Key: %s\n" key;

Printf.printf "Code: %s\n" ct;

Printf.printf "Back: %s\n" pt

;;

</lang>

{{out}}

<pre>

Text: Beware the Jabberwock, my son! The jaws that bite, the claws that catch!

Key: VIGENERECIPHER

Code: WMCEEIKLGRPIFVMEUGXQPWQVIOIAVEYXUEKFKBTALVXTGAFXYEVKPAGY

Back: BEWARETHEJABBERWOCKMYSONTHEJAWSTHATBITETHECLAWSTHATCATCH

</pre>