The Alphabet Cipher
Encyclopedia
Lewis Carroll
published The Alphabet-Cipher in 1868, possibly in a children's magazine. It describes what is known as a Vigenère cipher
, a well-known scheme in cryptography
. While Carroll calls this cipher "unbreakable", Kasiski had published a volume describing how to break such ciphers five years earlier, and Charles Babbage
had secretly found ways to break polyalphabetic cipher
s during the Crimean War
.
The piece begins with a tabula recta
.
A abcdefghijklmnopqrstuvwxyz A
B bcdefghijklmnopqrstuvwxyza B
C cdefghijklmnopqrstuvwxyzab C
D defghijklmnopqrstuvwxyzabc D
E efghijklmnopqrstuvwxyzabcd E
F fghijklmnopqrstuvwxyzabcde F
G ghijklmnopqrstuvwxyzabcdef G
H hijklmnopqrstuvwxyzabcdefg H
I ijklmnopqrstuvwxyzabcdefgh I
J jklmnopqrstuvwxyzabcdefghi J
K klmnopqrstuvwxyzabcdefghij K
L lmnopqrstuvwxyzabcdefghijk L
M mnopqrstuvwxyzabcdefghijkl M
N nopqrstuvwxyzabcdefghijklm N
O opqrstuvwxyzabcdefghijklmn O
P pqrstuvwxyzabcdefghijklmno P
Q qrstuvwxyzabcdefghijklmnop Q
R rstuvwxyzabcdefghijklmnopq R
S stuvwxyzabcdefghijklmnopqr S
T tuvwxyzabcdefghijklmnopqrs T
U uvwxyzabcdefghijklmnopqrst U
V vwxyzabcdefghijklmnopqrstu V
W wxyzabcdefghijklmnopqrstuv W
X xyzabcdefghijklmnopqrstuvw X
Y yzabcdefghijklmnopqrstuvwx Y
Z zabcdefghijklmnopqrstuvwxy Z
ABCDEFGHIJKLMNOPQRSTUVWXYZ
alphabet: thus, in the A column, the symbol is the same as the letter
represented; in the B column, A is represented by B, B by C, and so on.
To use the table, some word or sentence should be agreed on by two
correspondents. This may be called the 'key-word', or 'key-sentence',
and should be carried in the memory only.
In sending a message, write the key-word over it, letter for letter,
repeating it as often as may be necessary: the letters of the key-word
will indicate which column is to be used in translating each letter of
the message, the symbols for which should be written underneath: then
copy out the symbols only, and destroy the first paper. It will now be
impossible for any one, ignorant of the key-word, to decipher the message,
even with the help of the table.
For example, let the key-word be vigilance, and the message 'meet me on
Tuesday evening at seven', the first paper will read as follows—
v i g i l a n c e v i g i l a n c e v i g i l a n c e v i
m e e t m e o n t u e s d a y e v e n i n g a t s e v e n
h m k b x e b p x p m y l l y r x i i q t o l t f g z z v
The second will contain only 'h m k b x e b p x p m y l l y r x i i q t o l t f g z z v'.
The receiver of the message can, by the same process, retranslate it
into English.
If this table is lost, it can easily be written out from memory, by observing that the first symbol in each column is the same as the letter naming the column, and that they are continued downwards in alphabetical order. It would only be necessary to write out the particular columns required by the key-word, but such a paper would afford an adversary the means for discovering the key-word.
Lewis Carroll
Charles Lutwidge Dodgson , better known by the pseudonym Lewis Carroll , was an English author, mathematician, logician, Anglican deacon and photographer. His most famous writings are Alice's Adventures in Wonderland and its sequel Through the Looking-Glass, as well as the poems "The Hunting of the...
published The Alphabet-Cipher in 1868, possibly in a children's magazine. It describes what is known as a Vigenère cipher
Vigenère cipher
The Vigenère cipher is a method of encrypting alphabetic text by using a series of different Caesar ciphers based on the letters of a keyword. It is a simple form of polyalphabetic substitution....
, a well-known scheme in cryptography
Cryptography
Cryptography is the practice and study of techniques for secure communication in the presence of third parties...
. While Carroll calls this cipher "unbreakable", Kasiski had published a volume describing how to break such ciphers five years earlier, and Charles Babbage
Charles Babbage
Charles Babbage, FRS was an English mathematician, philosopher, inventor and mechanical engineer who originated the concept of a programmable computer...
had secretly found ways to break polyalphabetic cipher
Polyalphabetic cipher
A polyalphabetic cipher is any cipher based on substitution, using multiple substitution alphabets. The Vigenère cipher is probably the best-known example of a polyalphabetic cipher, though it is a simplified special case...
s during the Crimean War
Crimean War
The Crimean War was a conflict fought between the Russian Empire and an alliance of the French Empire, the British Empire, the Ottoman Empire, and the Kingdom of Sardinia. The war was part of a long-running contest between the major European powers for influence over territories of the declining...
.
The piece begins with a tabula recta
Tabula recta
In cryptography, the tabula recta is a square table of alphabets, each row of which is made by shifting the previous one to the left...
.
The Alphabet-Cipher, Lewis Carroll, 1868
ABCDEFGHIJKLMNOPQRSTUVWXYZA abcdefghijklmnopqrstuvwxyz A
B bcdefghijklmnopqrstuvwxyza B
C cdefghijklmnopqrstuvwxyzab C
D defghijklmnopqrstuvwxyzabc D
E efghijklmnopqrstuvwxyzabcd E
F fghijklmnopqrstuvwxyzabcde F
G ghijklmnopqrstuvwxyzabcdef G
H hijklmnopqrstuvwxyzabcdefg H
I ijklmnopqrstuvwxyzabcdefgh I
J jklmnopqrstuvwxyzabcdefghi J
K klmnopqrstuvwxyzabcdefghij K
L lmnopqrstuvwxyzabcdefghijk L
M mnopqrstuvwxyzabcdefghijkl M
N nopqrstuvwxyzabcdefghijklm N
O opqrstuvwxyzabcdefghijklmn O
P pqrstuvwxyzabcdefghijklmno P
Q qrstuvwxyzabcdefghijklmnop Q
R rstuvwxyzabcdefghijklmnopq R
S stuvwxyzabcdefghijklmnopqr S
T tuvwxyzabcdefghijklmnopqrs T
U uvwxyzabcdefghijklmnopqrst U
V vwxyzabcdefghijklmnopqrstu V
W wxyzabcdefghijklmnopqrstuv W
X xyzabcdefghijklmnopqrstuvw X
Y yzabcdefghijklmnopqrstuvwx Y
Z zabcdefghijklmnopqrstuvwxy Z
ABCDEFGHIJKLMNOPQRSTUVWXYZ
Explanation
Each column of this table forms a dictionary of symbols representing thealphabet: thus, in the A column, the symbol is the same as the letter
represented; in the B column, A is represented by B, B by C, and so on.
To use the table, some word or sentence should be agreed on by two
correspondents. This may be called the 'key-word', or 'key-sentence',
and should be carried in the memory only.
In sending a message, write the key-word over it, letter for letter,
repeating it as often as may be necessary: the letters of the key-word
will indicate which column is to be used in translating each letter of
the message, the symbols for which should be written underneath: then
copy out the symbols only, and destroy the first paper. It will now be
impossible for any one, ignorant of the key-word, to decipher the message,
even with the help of the table.
For example, let the key-word be vigilance, and the message 'meet me on
Tuesday evening at seven', the first paper will read as follows—
v i g i l a n c e v i g i l a n c e v i g i l a n c e v i
m e e t m e o n t u e s d a y e v e n i n g a t s e v e n
h m k b x e b p x p m y l l y r x i i q t o l t f g z z v
The second will contain only 'h m k b x e b p x p m y l l y r x i i q t o l t f g z z v'.
The receiver of the message can, by the same process, retranslate it
into English.
If this table is lost, it can easily be written out from memory, by observing that the first symbol in each column is the same as the letter naming the column, and that they are continued downwards in alphabetical order. It would only be necessary to write out the particular columns required by the key-word, but such a paper would afford an adversary the means for discovering the key-word.