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CAREADME.62
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1992-02-15
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QUAGMIRE TYPE II
REFERENCE: ACA, BRYAN, PERIODIC CIPHERS - MISCELLANEOUS
GAINES, CHAPTER 18
Initial entry requires the determination of the period, (# of cipher
alphabets used), which is a function of the keyword length used in the
enciphering phase.
This is accomplished by either the KASISKI method or the PHI TEST. The PHI
test sometimes fails where the PT does not follow the normal frequency
distribution. The KASISKI method may help here, by seeking the factors of
repeated digraphs or sequences, the longer sequences being preferable.
The CIPHER-ACE SERIES uses the Phi test method, as implemented in the
STATISTICAL TESTS, menu item 'X' of option 'E'.
After setting the correct period and displaying the message in period
format, an attempt is made to place a given tip or trial word (or likely
word fragments). Correct placement will develop good PT equivalents in the
message, and perhaps also in the KEYBLOCK.
An excellent procedure at this point would be the construction of contact
charts, frequency tables and a frequency graph of EACH period position (or
so-called column) as each column now represents a simple substitution
cipher.
The 'principle of assumptions' now dictates you assume equivalents in both
the keyblock and the CT message until you solve the message.
Perhaps the most important part of the de-crypters job is to now determine
the actual keyword(s) used. The keywords will pop out at you for the
simpler poly-alphabetics like the Vigenere. For the mixed alphabets, you
will have to apply KEYWORD RECOVERY procedures, as discussed particularly in
BRYAN.
For the type II Quag, the period setting keyword may be found in the CT
alphabet, each letter above the first letter beginning the PT alphabet.
The four classes of Quagmire are;
I. Keyed PT alphabet plus period setting keyword, straight CT alphabets
II. Keyed CT alphabets '' '' '' '' '' PT ''
III. Keyed PT and CT alphabets, same keyword plus a period keyword
IV. 3 Keywords, 1 each for PT, CT and period
Entry into the CT message begins with determining the period, either by use
of repeats or by the PHI test.
Frequency Counts of the resulting columns will aid in identifying
individual letters, and is very important. Each column is a simple
substitution cipher and may be attacked on that basis.
Placement of tips will give equivalent pairs which may be placed into
a skeleton KB (keyblock).
Menu Option 'A': The placement of a PT letter equivalent into the KB or
PT message, will automatically place that PT/CT pair into like period
positions. The KB will automatically re-generate the PT alphabets, when
a PT letter is found to be common to another PT alphabet.
The Quagmire Ciphers are of the Periodic Poly-alphabetic type.
The Ct message is stored on disk with NO spaces. If it is desired to
see the CT in 5 letter groups, simply set PERIOD to 5. When saved back
to the disk, it is again without the spaces.
Hardcopy will display the message in whatever period was last set.
When entering a CT message for saving, you may enter in 5 letter group
format, but spaces and punctuation will be stripped from the message.
The period may be from 2 to 26.
The period is set by the length of a keyword.
The work-page-display contains four components;
1. work-page-menu
2. KB (keyblock)
3. CT/PT display
4. work-page-prompt
1. work-page-menu. Consists of Options A-E.
A. PTASSIGN - input CT, PT, and CT alphabet. Updates KB and PT
B. Re-arrange columns. To bring out a second keyword.
C. SET PERIOD - Allows you to rapidly reconfigure for a new period.
Clears KB and PT.
D. TRIAL WORD - Clears KB and PT. Assigns a TIP or trial word(s)
to specific CT letters in the message.
Generates correct KB and PT fragments.
E. OPTION MENU -
A. save all memory messages back to disk, with work-in-progress
B. displays all caesar alphabets for enciphered tips
C. menu for multi-message operation
D. gives I.C. (index of coincidence) and PHI results for
appropriate cipher types
E. hardcopy of current message, formatted, 1 sheet
F. display and modify SIGINT file, data about the cipher
G. directory menu, with options for different file .EXT's
H. clear PT
I. readme - reads text files about this cipher, and in general
Y. return to main menu or forth
Z. return to dos
end.