alphabet-cipher

Lewis Carroll published a cipher known as The Alphabet Cipher

This Alphabet Cipher involves alphabet substitution using a keyword.

First you must make a substitution chart like this, where each row of the alphabet is rotated by one as each letter goes down the chart.

   ABCDEFGHIJKLMNOPQRSTUVWXYZ
 A abcdefghijklmnopqrstuvwxyz
 B bcdefghijklmnopqrstuvwxyza
 C cdefghijklmnopqrstuvwxyzab
 D defghijklmnopqrstuvwxyzabc
 E efghijklmnopqrstuvwxyzabcd
 F fghijklmnopqrstuvwxyzabcde
 G ghijklmnopqrstuvwxyzabcdef
 H hijklmnopqrstuvwxyzabcdefg
 I ijklmnopqrstuvwxyzabcdefgh
 J jklmnopqrstuvwxyzabcdefghi
 K klmnopqrstuvwxyzabcdefghij
 L lmnopqrstuvwxyzabcdefghijk
 M mnopqrstuvwxyzabcdefghijkl
 N nopqrstuvwxyzabcdefghijklm
 O opqrstuvwxyzabcdefghijklmn
 P pqrstuvwxyzabcdefghijklmno
 Q qrstuvwxyzabcdefghijklmnop
 R rstuvwxyzabcdefghijklmnopq
 S stuvwxyzabcdefghijklmnopqr
 T tuvwxyzabcdefghijklmnopqrs
 U uvwxyzabcdefghijklmnopqrst
 V vwxyzabcdefghijklmnopqrstu
 W wxyzabcdefghijklmnopqrstuv
 X xyzabcdefghijklmnopqrstuvw
 Y yzabcdefghijklmnopqrstuvwx
 Z zabcdefghijklmnopqrstuvwxy

Both parties need to decide on a secret keyword. This keyword is not written down anywhere, but memorized.

To encode the message, first write down the message.

meetmebythetree

Then, write the keyword, (which in this case is scones), repeated as many times as necessary.

sconessconessco
meetmebythetree

Now you can look up the column S in the table and follow it down until it meets the M row. The value at the intersection is the letter e. All the letters would be thus encoded.

sconessconessco
meetmebythetree
egsgqwtahuiljgs

The encoded message is now egsgqwtahuiljgs

To decode, the person would use the secret keyword and do the opposite.

License

Copyright © 2014 Jackson Tong

Distributed under the Eclipse Public License either version 1.0 or (at your option) any later version.