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Ancient Roots*
Secrets are the very root of cool.
—William Gibson, Spook Country
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1.1 Caveman
aveman Crypto
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Various records from cultures before that of classical Greece are sometimes
included in texts as examples of cryptography, but the term must be used
loosely, as the methods are extremely primitive. How far back one looks for
the origins of cryptology depends on how far one is willing to stretch defini
definitions. Most authors would agree that Henry E. Langen went back a bit too far
in his Cryptanalytics—A Course in Cryptography:
Cryptography
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Early cavemen may have developed a system of secret oral grunts or
mimetic signs to convey messages to one another.
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Female
55–Antu
45–Ninlil
35–Ninki
25–Ningal
15–Inanna/Ishtar
5–Ninhursag
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Male
60–Anu
50–Enlil
40–Ea/Enki
30–Nanna/Sin
20–Utu/Shamash
10–Ishkur/Adad
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We shall be content to begin in ancient Sumer with an example of “protocryptography.” The Sumerians recognized many gods, but only 12 were part
of the “Great Circle.” Six of these were male and six female.
The number paired with the name of the god was sometimes used instead
of the name;† thus, we have a substitution cipher. In general, though, as
explained in the Introduction, when entire words or names are swapped out
for numbers or letters, we refer to that as a code rather than a cipher.
*
†
A link leading to exercises for this chapter may be found at http://www.crcpress.com/
product/isbn/9781466561861.
Röllig, Werner, and Götterzahlen, in Ebeling, E. and Meissner, B., Eds., Reallexikon der
Assyriologie und Vorderasiatischen Archäologie, Vol. 3, Walter de Gruyter & Co., Berlin, 1971,
pp. 499–500.
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Secret History: The Story of Cryptology
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Figure 1.1
A skytale reveals a message.
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It seems that every culture that develops writing (which itself offers some
secrecy if nearly everyone is illiterate) develops cryptography soon thereaf
thereafter. Although many more examples could be included, we now move on to
the ancient Greeks’ use of cryptography.
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1.2.1 Skytale Cipher
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1.2 Greek Cryptography
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The skytale (pronounced to rhyme with “Italy”), shown in Figure 1.1, was
used in 404 B.C. by the Spartans. The message sent to Lysander warned of a
planned attack by Pharnabazus of Persia.* This warning provided Lysander
with sufficient time to prepare a successful defense.
Although this historical example has been recounted by many authors, a
dissenting view has been offered by Thomas Kelly, a professor of Greek histohisto
ry.† Kelly examined the earliest extant appearances of the word “skytale” and
concluded that it merely stood for “either a plaintext message or a device for
keeping records.” He claimed that later usage indicating a device for enciphering was a misinterpretation and that the skytale never had such a purpose.
In any case, the idea is to wrap a strip of paper‡ around a staff and then
write the message out in rows aligned with the staff. When the paper is
taken off the staff, the order of the letters changes. This is a transposition
cipher (the letters are not changed, only their order, in contrast to a substitution cipher). Anyone with a staff of diameter equal to the original can recover
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*
†
‡
Singh, S., The Code Book, Doubleday, New York, 1999, p. 9.
Kelly, T., The myth of the skytale, Cryptologia, 22(3), 244–260, 1998.
The Greeks reportedly used a leather strip, sometimes disguised as a belt.
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Ancient Roots
Figure 1.2
American Cryptogram Association logo (www.cryptogram.org/).
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the message. An alternate spelling of this simple device is “scytale.” These
variations are natural when one considers that the word is of Greek origin.
The original is σκυταλε. The American Cryptogram Association (which celebrated its 80th anniversary in 2010) uses a skytale in their logo (Figure 1.2).
It has been conjectured that the skytale marks the origin of the commander’s
baton, which became purely symbolic.
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1.2.2 Polybius
olybius Cipher
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Another example of Greek cryptography is the Polybius cipher.* This cipher
has the disadvantage of doubling the length of the message.
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I&J
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In the Polybius cipher, each letter is replaced by the position in which it
appears in the square, using first the row number and then the column num
number. An example is
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T H I S I S E A S Y T O B R E A K
44 23 24 43 24 43 15 11 43 54 44 34 12 42 15 11 25
s
This system was originally intended for signaling over long distances. To
send the first letter, T, one would hold 4 torches in the right hand and 4 in
the left. To send the next letter, H, one would hold 2 torches in the right hand
and 3 in the left. We will see how to break such a cipher in Chapter 2. It’s a
special case of a general class of ciphers known as monoalphabetic substitution
ciphers, where a given letter is always substituted for with the same symbol
wherever it appears.
The five-by-five square forced us to combine I and J as 24. The Greeks,
using a smaller alphabet, did not have this inconvenience. For us, though,
decipherment is not unique, but context should make clear which choice is
*
Polybius wrote about this system in Chapter 46 of his tenth book of history, circa 170 BC.
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Secret History: The Story of Cryptology
correct. Of course, we could use a six-by-six square, which would allow for
26 letters and 10 digits. Alternatively, numbers can be spelled out. A six-bysix square would be used for languages written in the Cyrillic alphabet. The
Hawaiian alphabet, on the other hand, contains only 12 letters: 5 vowels (a, e,
i, o, u) and 7 consonants (h, k, l, m, n, p, w). Thus, for the Hawaiian alphabet,
a four-by-four square would suffice.
The Polybius square is sometimes called a Polybius checkerboard. The letters may be placed in the square in any order; for example, the keyword
DERANGEMENT could be used to rearrange the letters like so:
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2
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A
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2
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M
T
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Observe that repeated letters of the keyword are left out when they reappear.
Once the keyword is used up, the remaining letters of the alphabet are filled
in the square.
The term derangement has a technical meaning, in that it refers to a reor
reordering where no object occupies its original position. Thus, the scrambling
provided above is not a derangement, since the letters U, V, W, X, Y, and Z are
left in their original locations.
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1.3 Viking Cryptography
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Markings on the Swedish Rotbrunna stone, shown in Figure 1.3, may appear
meaningless, but they are actually an example of Viking cryptography. If
we note the numbers of long strokes and short strokes in each group, we get
the numbers 2, 4, 2, 3, 3, 5, 2, 3, 3, 6, 3, 5. Pairing these numbers gives us 24,
23, 35, 23, 36, 35. Now consider Figure 1.4. The Vikings used diagrams like
these to translate the numbers to runes; for example, 24 indicates the second
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Figure 1.3
Example of Viking cryptography. (Redrawn from Franksen, O.I., Mr. Babbage’s Secret: The Tale of
a Cypher—and APL, Prentice Hall, Englewood Cliffs, NJ, 1984.)
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Ancient Roots
member
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2
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(th)
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member
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(th)
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aeht
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Figure 1.4
Examples of Pre-Viking (left) and Viking (right) cryptography.
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row and fourth column. In the diagram on the left, this gives the rune for J.
Thus, this encryption system was essentially a Polybius cipher. This is just
one of the Viking systems; there are others. Secrecy must have been impor
important for these people from the beginning, for the word rune means “secret”
in Anglo-Saxon.
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1.4 Early Steganography
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The Greeks also made use of steganography. In 480 BC, they received advance
warning of an attack by the Persians launched by King Xerxes. Herodotus
explained how this was achieved:*
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As the danger of discovery was great, there was only one way in which
he could contrive to get the message through: this was by scraping the
wax off a pair of wooden folding tablets, writing on the wood under
underneath what Xerxes intended to do, and then covering the message over
with wax again. In this way the tablets, being apparently blank, would
cause no trouble with the guards along the road. When the message
reached its destination, no one was able to guess the secret until, as I
understand, Cleomenes’ daughter Gorgo, who was the wife of Leonidas,
discovered it and told the others that, if they scraped the wax off, they
would find something written on the wood underneath. This was done;
the message was revealed and read, and afterwards passed on to the
other Greeks.
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The warning, combined with the efforts of 300 Spartans who held off
the Persians for three days, allowed time to prepare a successful defense.
Leonidas was among those who died trying to gain the time necessary for
*
Herodotus, The Histories, Book 7: Polymnia, Section 239.
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Secret History: The Story of Cryptology
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the Greeks to build a stronger defense. Without the advance warning given
in this instance (or for the later attack, mentioned previously, where the
skytale was used to convey a warning), it’s conceivable that a lack of preparation could have led to a victory for Persia, in which case there would have
been no “cradle of Western civilization.”
Another steganographic trick was carried out by Histaieus. In 499 BC,
he had a slave’s head shaved for the purpose of tattooing a message on it
encouraging Aristagoras of Miletus to revolt against the Persian king. When
the slave’s hair grew back, concealing the message, the slave was dispatched
with instructions to tell the intended recipient to shave his head. This is not
a good method, though, if time is of the essence or if the message is long and
the slave’s head small!*
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References and Further Reading
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Balliett, B., Chasing Vermeer,, Scholastic Press, New York, 2004. This is a young adult/
children’s novel that incorporates a Polybius cipher that mixes letters and num
numbers by using the following (non-square) rectangle for enciphering:
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Thus, HELLO would become V1 P1 Z1 Z1 L2. The book promotes free thinking
and exploration in the spirit of Charles Fort, who is quoted at various points.
Bellovin, S.M., Compression, Correction, Confidentiality, and Comprehension: A Modern
Look at Commercial Telegraph Codes, Department of Computer Science, Columbia
University, NY, 2009 (http://www.usenix.org/events/sec09/tech/slides/bellovin.pdf). This PowerPoint® presentation on commercial code books provides
many entertaining examples, such as this excerpt from The Theatrical Cipher Code
(1905):
*
Herodotus, The Histories, Book 5: Terpsichore, Section 35.