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Affine Cipher

simple affineCipher translated from https://github.com/asweigart/codebreaker/blob/master/affineCipher.py not sure if actually correct. I updated the below to make it easier to understand because I was bored, made some more changes, now pass in lambda as function to pxn instead of individual functions, as suggested by rwbarton for my haskell version.

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(* Affine Cipher - origional in python from http://inventwithpython.com/codebreaker (BSD Licensed) *)
let flip f a b = f b a

let findModInverse a m =
  [0..m] 
  |> Seq.filter (fun b -> a * b % m = 1)  
  |> Seq.head        

let findIndex (s : string) (c : char) =
  s.IndexOf c

let px (s : string) f x g y =
  Seq.map (findIndex s
     >> flip   f x 
     >>        g y 
     >> flip   (%) s.Length
     >> flip Seq.nth s
     >> string)

type Mode = Encrypt | Decrypt

let f M a b =             
  let x = px "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
  let i = findModInverse a 26
  
  match M with
    Encrypt -> x ( * ) a ( + ) b
  | Decrypt -> x ( - ) b ( * ) i

let enc : string -> string = f Encrypt 1 2 >> String.concat ""

let dec : string -> string = f Decrypt 1 2 >> String.concat ""

assert (enc "TEST" = "VGUV")
assert (dec (enc "TEST") = "TEST")

val flip : f:('a -> 'b -> 'c) -> a:'b -> b:'a -> 'c

Full name: Script.flip

val f : ('a -> 'b -> 'c)

val a : 'b

val b : 'a

val findModInverse : a:int -> m:int -> int

Full name: Script.findModInverse

val a : int

val m : int

module Seq

from Microsoft.FSharp.Collections

val filter : predicate:('T -> bool) -> source:seq<'T> -> seq<'T>

Full name: Microsoft.FSharp.Collections.Seq.filter

val b : int

val head : source:seq<'T> -> 'T

Full name: Microsoft.FSharp.Collections.Seq.head

val findIndex : s:string -> c:char -> int

Full name: Script.findIndex

val s : string

Multiple items
val string : value:'T -> string

Full name: Microsoft.FSharp.Core.Operators.string

--------------------
type string = System.String

Full name: Microsoft.FSharp.Core.string

val c : char

Multiple items
val char : value:'T -> char (requires member op_Explicit)

Full name: Microsoft.FSharp.Core.Operators.char

--------------------
type char = System.Char

Full name: Microsoft.FSharp.Core.char

System.String.IndexOf(value: string) : int
System.String.IndexOf(value: char) : int
System.String.IndexOf(value: string, comparisonType: System.StringComparison) : int
System.String.IndexOf(value: string, startIndex: int) : int
System.String.IndexOf(value: char, startIndex: int) : int
System.String.IndexOf(value: string, startIndex: int, comparisonType: System.StringComparison) : int
System.String.IndexOf(value: string, startIndex: int, count: int) : int
System.String.IndexOf(value: char, startIndex: int, count: int) : int
System.String.IndexOf(value: string, startIndex: int, count: int, comparisonType: System.StringComparison) : int

val px : s:string -> f:(int -> 'a -> 'b) -> x:'a -> g:('c -> 'b -> int) -> y:'c -> (seq<char> -> seq<string>)

Full name: Script.px

val f : (int -> 'a -> 'b)

val x : 'a

val g : ('c -> 'b -> int)

val y : 'c

val map : mapping:('T -> 'U) -> source:seq<'T> -> seq<'U>

Full name: Microsoft.FSharp.Collections.Seq.map

property System.String.Length: int

val nth : index:int -> source:seq<'T> -> 'T

Full name: Microsoft.FSharp.Collections.Seq.nth

type Mode =
| Encrypt
| Decrypt

Full name: Script.Mode

union case Mode.Encrypt: Mode

union case Mode.Decrypt: Mode

val f : M:Mode -> a:int -> b:int -> (seq<char> -> seq<string>)

Full name: Script.f

val M : Mode

val x : ((int -> int -> int) -> int -> (int -> int -> int) -> int -> seq<char> -> seq<string>)

val i : int

val enc : (string -> string)

Full name: Script.enc

module String

from Microsoft.FSharp.Core

val concat : sep:string -> strings:seq<string> -> string

Full name: Microsoft.FSharp.Core.String.concat

val dec : (string -> string)

Full name: Script.dec

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More information

Link:	http://fssnip.net/dy
Posted:	12 years ago
Author:	david klein
Tags:	affine