Cryptography Reference
In-Depth Information
1.4
Cryptology and the Arabs
He shall live, and unto himshall be given all the gold of Arabia
.
The Topic of Common Prayer (1662)
,
Psalm72, v. 15
In this section, we will learn how the flourishing Arab civilization discovered
cryptanalytic techniques and published the first systematic analysis of it and
of cryptology proper. The earliest known contribution from Arab civilization
comes from an author of 725 (unless otherwise specified, we will be talking about
dates
AD
, henceforth), Abu 'Abd al-Ra
.
man al-Kahalıl ibn A
.
mad ibn 'Amr
ibn Tammam al Farahıdı al-ZadıalYa
.
madı, who wrote the
Kitab al-mu'amma
.
This writing was inspired by a cryptogram, written in Greek, sent to him by
the Byzantine emperor. It is purported that his reasoning for its solution went
along the lines of assuming that the cryptogram began with words similar to
“In the name of God...” and he was able to deduce the first few letters based
upon this assumption. He worked from there to decrypt the entire message.
Ostensibly, this took him one month to solve. Arab cryptanalysis was in its
infant stages, but that would change.
The Arabs' invention of cryptanalysis was rooted in religious scholarship
where theologians analyzed the Koran, trying to establish the time line of events,
by counting the frequencies of words contained in each of Muhammad's reve-
lations. Their reasoning was that if a high frequency of certain more recently
evolved words were found in a given revelation, then that would be one to place
later in the time line. They also looked at the commonality of letters, among
other aspects of cryptanalysis that we consider to be fundamental today. Their
earliest known description of such letter frequency analysis was created in the
ninth-century by the author Ab¯uYusufYa'qub ibn Is-haq ibn as-Sabbah ibn
'omran ibn Ismaıl al-Kindı (but, we will just call him al-Kindı). His treatise
is entitled
A Manuscript on Deciphering Cryptographic Messages
, rediscovered
in the Sulaimaniyyah Ottoman Archive in Istanbul in 1987. Although al-Kindı
wrote nearly three hundred topics on various topics including mathematics and
medicine,
our
interest is in the cryptanalytic text since it represents the first
recorded instance of a treatise on cryptanalysis involving “letter frequencies”.
In order to understand what al-Kindı discovered in the realm of letter fre-
quency analysis and to set up our discussions for later analysis in the text, let us
look at the English language from the perspective of most frequently occurring
words, and letters.
The statistical data shown in Table 1.4 are taken from this author's book
[170, page 203]. The most common words in order of frequency distribution are:
Frequency of Words in English
THE, OF, ARE, I, AND, YOU, A, CAN, TO, HE,
Table 1.4
HER, THAT, IN, WAS, IS, HAS, IT, HIM, HIS
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