The Bifid cipher is considered a more secure cipher because it breaks the
message apart into two separate streams and then recombines them. This
spreads the information out to multiple letters, increasing security. It
uses a table with one letter of the alphabet omitted. Often the J is
removed and people just use an I instead. Below is an unkeyed grid.
|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
To encode a message, you would write your message, "ABCD", then you would
figure out the row and column for each letter and write them below the
letters, like the example shows. Then you read the numbers off; all of the
rows first and then all of the columns. Using this string of numbers, you
then look up the letters on the table again and get the encoded message.
|letter: A B C D|
row: 1 1 1 1
column: 1 2 3 4
The numbers: 1 1 1 1 1 2 3 4
Encoded: A A B
All non-letters are ignored and not encoded. The one skipped letter will
be automatically translated if you type it in the box. Numbers, spaces, and
punctuation will remain in place and will not be encoded.
You can see the example
message, or the example from Wikipedia.