Vigenère Squares

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 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 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 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 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
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
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
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 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
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
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
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
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
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 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
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
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
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
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
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
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
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 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 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 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 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
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 Vigenère Cipher is a complicated combination of Caesar Ciphers. To encipher a secret message, say meet at seven here, you first need a keyword e.g. LATER. Write out the message with the keyword written above it. Encipher each letter by finding it in the top row (red) and following that column down until it hits the row  of the keyword character (green) – e.g. L’s row for m. They intersect at X, the code. Our example would look like this:

L A T E R L A T E R L A T E R
m e e t a t s e v e n h e r e
X E X X R E S X Z V Y H X V V

So our cipher would be:

XEXXRESXZVYHXVV

To crack Vigenère ciphers, where the keyword is known, simply seek out the pink letter in the green row. Then look up to the top of the intersection column for the decryption.

But if you don’t know the keyword, look for repeated phrases to give you the length of the keyword. If there are repeats 8 letters apart, then the key must be 8, 4 or 2 letters long (1 would be a simple Caesar Cipher).  If it is 4 letters long, then you have four alternating Caesar ciphers.

Separate them, then look for the most common letters as usual. Once you have solved two of them, you have two of the keyword’s letters and can hopefully start to guess it, or at least rule possibilities out.

Can you solve this puzzle?     Vigenère Puzzle