Vigenere Cipher

Vigenere Cipher Encoder/Decoder Table

 
				Keyword Letters

   	    A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

	A   A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
	B   B C D E F G H I J K L M N O P Q R S T U V W X Y Z A 
	C   C D E F G H I J K L M N O P Q R S T U V W X Y Z A B
	D   D E F G H I J K L M N O P Q R S T U V W X Y Z A B C 
	E   E F G H I J K L M N O P Q R S T U V W X Y Z A B C D 
  P	F   F G H I J K L M N O P Q R S T U V W X Y Z A B C D E 
  l	G   G H I J K L M N O P Q R S T U V W X Y Z A B C D E F 
  a	H   H I J K L M N O P Q R S T U V W X Y Z A B C D E F G 
  i	I   I J K L M N O P Q R S T U V W X Y Z A B C D E F G H 
  n	J   J K L M N O P Q R S T U V W X Y Z A B C D E F G H I 
  t	K   K L M N O P Q R S T U V W X Y Z A B C D E F G H I J 
  e	L   L M N O P Q R S T U V W X Y Z A B C D E F G H I J K 
  x	M   M N O P Q R S T U V W X Y Z A B C D E F G H I J K L 
  t	N   N O P Q R S T U V W X Y Z A B C D E F G H I J K L M 
	O   O P Q R S T U V W X Y Z A B C D E F G H I J K L M N 
  L	P   P Q R S T U V W X Y Z A B C D E F G H I J K L M N O 
  e	Q   Q R S T U V W X Y Z A B C D E F G H I J K L M N O P 
  t	R   R S T U V W X Y Z A B C D E F G H I J K L M N O P Q 
  t	S   S T U V W X Y Z A B C D E F G H I J K L M N O P Q R  
  e	T   T U V W X Y Z A B C D E F G H I J K L M N O P Q R S 
  r	U   U V W X Y Z A B C D E F G H I J K L M N O P Q R S T 
  s	V   V W X Y Z A B C D E F G H I J K L M N O P Q R S T U
	W   W X Y Z A B C D E F G H I J K L M N O P Q R S T U V 
	X   X Y Z A B C D E F G H I J K L M N O P Q R S T U V W 
	Y   Y Z A B C D E F G H I J K L M N O P Q R S T U V W X 
	Z   Z A B C D E F G H I J K L M N O P Q R S T U V W X Y 


To Encode: 

1. Write the keyword repeatedly, letter for letter, over the plain text. 
2. For each letter, find the column marked with the keyword letter
   and the row marked with the plain text letter.  Choose the letter
   in the chart where the row and column intersect. 

To Decode: 

1. Write the keyword repeatedly, letter for letter, over the plain text. 
2. For each letter, find the column marked with the keyword letter and
   follow it down until you find the cipher text letter.  Choose the letter
   that is the label for that row.  

Exercises: 

1. Encode the plain text "CAMBRIDGE" with the key "CRLS": 

2. Decode the cipher text "XXBCVPCK" with the key "TODAY":  

3. Challenge: Can you think of a way to crack the Vigenere cipher if you didn't 
know the key?  (It took from the 1500s to the 1800s for anyone to come up 
with a way to break it!)