Wolfram Function Repository

Instant-use add-on functions for the Wolfram Language

Function Repository Resource:

 AffineDecipher

Source Notebook

Decipher a string using the affine cipher

Contributed by: Sander Huisman

ResourceFunction["AffineDecipher"][string,{a,b}]

deciphers string using the affine cipher with parameters a and b.

ResourceFunction["AffineDecipher"][{a,b}]

represents an operator form of ResourceFunction["AffineDecipher"] that can be applied to an expression.

Details and Options

For the affine cipher, the letters "a"–"z" are numbered 0–25. Each character in string is converted to a number x using the aforementioned numbering. Each number is then transformed by computing (ax+b)mod26. The new numbers are then reinterpreted as letters.
Here is an example enciphering the letters "A"–"Z" for a=5 and b=8. Deciphering is done by reading the diagram from bottom to top.
The case of the letters is retained by ResourceFunction["AffineDecipher"].

Examples

Basic Examples (1) 

Convert a simple text:

In[1]:=
ResourceFunction["AffineDecipher"]["ihhwvc swfrcp", {5, 8}]
Out[1]=

Scope (2) 

AffineDecipher automatically maps over a list of strings:

In[2]:=
ResourceFunction[ "AffineDecipher"][{"zrwu", "wu", "i", "zcuz"}, {5, 8}]
Out[2]=

Create an operator:

In[3]:=
op = ResourceFunction["AffineDecipher"][{5, 8}]
Out[3]=

Apply the operator to a string:

In[4]:=
op["nillaav"]
Out[4]=

Properties and Relations (2) 

The Caesar decipher can be recreated using the affine decipher by choosing a=1:

In[5]:=
string = "Bpqa qa rcab i bmab"; {ResourceFunction["AffineDecipher"][string, {1, 8}], ResourceFunction["CaesarDecipher"][string, 8]}
Out[5]=

AffineDecipher could be recast in terms of the resource function AffineCipher:

In[6]:=
enciphered = "ihhwvc swfrcp"; deciphered = ResourceFunction["AffineDecipher"][enciphered, {5, 8}]
Out[6]=

Again decipher, this time using AffineCipher with appropriate parameter values for inverting:

In[7]:=
minv = ModularInverse[5, 26]; ResourceFunction["AffineCipher"][enciphered, {minv, -8 minv}]
Out[7]=

Possible Issues (2) 

The parameter a must be coprime to 26:

In[8]:=
ResourceFunction["AffineDecipher"]["vlyetg mzbvjly", {14, 11}]
Out[8]=

Some of the permissible values for a are:

In[9]:=
Select[Range[100], CoprimeQ[#, 26] &]
Out[9]=

Publisher

SHuisman

Version History

  • 1.0.0 – 07 August 2019

Related Resources

License Information