Basic Examples

Decipher a message using the key “lemon”:
[◼]
VigenereDecipher
["LXFOPVEFRNHR","LEMON"]
In[]:=
ATTACKATDAWN
Out[]=
Decipher with multiple keys:
[◼]
VigenereDecipher
["ZKYWUTTLKFMFZSLIFDWFYCXEQQDVZSHQHZVA",{"zoology","abbreviated","acquaintances"}]
In[]:=
ATTACKATDAWNATTACKATDAWNATTACKATDAWN
Out[]=

Scope

Decipher a message twice, first using “GO” and then with “CAT”:
[◼]
VigenereDecipher
["IHSQIRIHCQCU",{"GO","CAT"}]
In[]:=
ATTACKATDAWN
Out[]=
Decipher multiple strings:
[◼]
VigenereDecipher
[{"Tdak","Upr","Haaeo"},"sparks"]
In[]:=
{Boat,Car,Plane}
Out[]=
Create an operator that deciphers strings with the key ‘sparks’:
op=
[◼]
VigenereDecipher
["sparks"]
In[]:=
[◼]
VigenereDecipher
[sparks]
Out[]=
Apply the operator to a string:
op["Lwe lgsi wvgsis"]
In[]:=
The boat floats
Out[]=

Properties and Relations

If a single character is used, the Vigenère’s cipher is identical to a Caesar’s cipher:
[◼]
VigenereDecipher
["ATTACKATDAWN","D"]ResourceFunction["CaesarCipher"]["ATTACKATDAWN",-3]
In[]:=
True
Out[]=
When deciphering with multiple keys, the keys can first be enciphered with each other to decipher the message with a single key. The length of the replacing key has to be the
LCM
of the lengths of each of the keys:
newkey=ResourceFunction["VigenereCipher"]["CATCAT","GO"]
In[]:=
IOZQGH
Out[]=
This indeed matches with what you expect:
[◼]
VigenereDecipher
["IHSQIRIHCQCU",newkey]==
[◼]
VigenereDecipher
["IHSQIRIHCQCU",{"CATCAT","GO"}]
In[]:=
True
Out[]=
The case of the original text is retained, the case of the key does not matter:
[◼]
VigenereDecipher
["VhbuIlCwxuofg","CAT"]
In[]:=
ThisIsAwesome
Out[]=
[◼]
VigenereDecipher
["VhbuIlCwxuofg","cat"]
In[]:=
ThisIsAwesome
Out[]=
VigenereDecipher
is related to
VigenereCipher
:
[◼]
VigenereDecipher
[ResourceFunction["VigenereCipher"]["ATTACKATDAWN","LEMON"],"LEMON"]
In[]:=
ATTACKATDAWN
Out[]=

Possible Issues

Spaces and the letters “a” and “A” in the key will not alter the enciphered message:
[◼]
VigenereDecipher
["DNESIASY","a A"]
In[]:=
DNESIASY
Out[]=
The key should have valid letters and valid length:
[◼]
VigenereDecipher
["LXFOPVEFRNHR","niño"]
In[]:=
VigenereDecipher
::invalidkey
:The key(s) {niño} should be made up of characters a—z, A—Z, and spaces, and have a minimum length of 1.
$Failed
Out[]=
[◼]
VigenereDecipher
["LXFOPVEFRNHR","Ευκλείδης"]
In[]:=
VigenereDecipher
::invalidkey
:The key(s) {Ευκλείδης} should be made up of characters a—z, A—Z, and spaces, and have a minimum length of 1.
$Failed
Out[]=
[◼]
VigenereDecipher
["LXFOPVEFRNHR",""]
In[]:=
VigenereDecipher
::invalidkey
:The key(s) {} should be made up of characters a—z, A—Z, and spaces, and have a minimum length of 1.
$Failed
Out[]=
Two keys can ‘negate’ each other:
[◼]
VigenereDecipher
["LXFOPVEFRNHR",{"LEMON","PWOMN"}]
In[]:=
Enciphering the keys with each other gives a string with only ‘A’s: