What is the Beaufort Cipher?

Choose a keyword. Write the plaintext in horizontal rows under the keyword, with each row being the same length as the keyword. Use a tableau, using the row that corresponds to the keyword letter, and the column that corresponds to the plaintext letter.

Example

Plaintext: Whoever has made a voyage up the Hudson must remember the Kaatskill mountains.

Keyword: RIPVANWINKLE

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

Encipher step

R I P V A N W I N K L E
W H O E V E R H A S M A
D E A V O Y A G E U P T
H E H U D S O N M U S T
R E M E M B E R T H E K
A A T S K I L L M O U N
T A I N S

Ciphertext:
VBBRF JFBNS ZEOEP AMPWC JQWLK EIBXV IVBQT LAEDR OMSRU DHURI WDQFL XBWRR YIHII

Vulnerabilities of Beaufort Cipher

Doing an analysis of Periodic ICs can help reveal potential keyword lengths, as can the Kasiski Examination.

How to Crack a Beaufort Cipher

The Kasiski Examination can be performed: look for repeated sequences in the ciphertext and factor the distance between them. This gives potential keyword lengths. Placing the ciphertext into columns with the width of those lengths allows one to perform a frequency analysis on each column to help determine which alphabet was used for that column.