(2012-11-21)
Simple Shift Ciphers: The easiest codes to break.
Caesar's cipher. Augustus cipher. Modern ROT13.
Strictly speaking, Caesar's cipher was a fixed monalphabetic substitution method based on the Roman
alphabet (Classical Latin alphabet) of
23 letters (omitting J, U and W from the modern Latin alphabet of 26 letters). It consisted in replacing
every letter by the letter appearing three ranks further in the alphabet:
Caesar's cipher used the Roman alphabet of 23 letters :
Plaintext
A
B
C
D
E
F
G
H
I
K
L
M
N
O
P
Q
R
S
T
V
X
Y
Z
Ciphertext
D
E
F
G
H
I
K
L
M
N
O
P
Q
R
S
T
V
X
Y
Z
A
B
C
ROT13 is the only symmetrical shift cipher in the Latin alphabet of 26 letters.
The device designed by
Leon Battista Alberti (1404-1472)
was used for secret transmission within the Vatican.
It uses two different extensions of the Latin alphabet for the plain text and the cipher text.
(2012-11-21) The Vigenère Cipher
A polyalphabetic cipher devised by Blaise de Vigenère.
It was once known as le chiffre indéchiffrable
(the unbreakable cipher).
It was re-invented many times and its good reputation is not deserved:
The so-called Babbage-Kasisky method cab easily crack it, at least if the
encoding key is much shorter than the text.
(2012-11-21) The German Enigma machines.
Codes broken by Poland and the UK before and during WWII.
The enigma machine was invented in 1918 by
Arthur Cherbius (1878-1929).
In spite of its high cost, it was eventually adopted by the German military
once it was revealed that the British had been able to crack the military German codes during WWI
(that revelation was published in a book by Winston Churchill).
Instrumental in that German decision to adopt a new coding technology was the future
Panzer GeneralRudolf Schmidt (1886-1957) whose younger brother
Hans-Thilo Schmidt (1888-1943)
would eventually sell enigma secrets to a French operative codenamed
Rex, under the cryptonym of
Asché or Source-D.
The information received from Asché was communicated to
the Polish cipher-bureau who could use it to figure out the internal wiring of the
enigma rotors.
The Polish mathematician Marian
Rejewski (1905-1980)
used this, together with the weakness introduced by the systematic repetition of the first
trigram in the original standard Enigma protocol, to crack enigma codes in 1932.
Poland communicated that information back to France and the UK, where
Alan Turing (1912-1954)
could crack the codes even after the Germans had stopped repeating the first
trigrams in their messages (in a way, Rejewski's ultimate contribution was
to convince the British that enigma codes were breakable even if fewer weaknesses
could be exploited).
(2012-12-22) The mysterious Voynich manuscript :
Written on fine parchment carbon-dated between 1408 and 1438.
In 1912, this 200-page manuscript was acquired from
Villa Mondragone, near Rome, by an antiques dealer from London
who would move to New-York in 1914,
Wilfrid Voynich (1865-1930).
Né Michal Habdank-Wojnicz, he was a Polish-Lithuanian revolutionary who had escaped from penal servitude
in Siberia and established himself in London in 1890. In 1898, he married
Ethel Lilian Boole (1864-1960)
daughter of Mary Everest Boole (1862-1916,
niece of George Everest)
and of the great mathematician George Boole (1815-1864)
who died when she was 4 months old...
This mathematical connection may have played a rôle in building the early belief
that the manuscript was written in some common language but encoded with a secret cipher
to hide sensitive information not meant for the uninituated.
This hypothesis is all but abandonned now.
What's now believed by an increasing number of scholars and amateurs alike is that
the manuscript is a unique sample of a script invented to transcribe an unidentified
Indo-European language or dialect for which no other script is known.
The many botanical and astronomical illustrations in the Voynich manuscript offer
some hope of identifying some scientific words and their Indo-European roots.
This leads to a partial decoding of the Voynich alphabet in terms of associated sounds.
Along those promising lines, Stephen Bax
has tentatively identified 10 words and 14 letters (or groups of letters).
(video 47:11).
