The Vigenère Tableau

   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
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 E F
G  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  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  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  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  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  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  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  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  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  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  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  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  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  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  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  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

Vigenère

The leftmost column has the keys; the top alphabet has the plaintext. So:

message HELLOWORLD
key     ECSECSECSE
cipher  LGDPQOSTHD

Beaufort

Find the plaintext in the left alphabet, and trace in until you find the key letter. Then turn a right angle and go up. The letter at the top alphabet is the ciphertext.

message HELLOWORLD
key     ECSECSECSE
cipher  WYHSOWPLHB

Variant Beaufort

Find the key letter in the left alphabet, and trace in until you find the plaintext letter. Then turn a right angle and go up. The letter at the top alphabet is the ciphertext.

message HELLOWORLD
key     ECSECSECSE
cipher  DCTHMEKPTZ