Quagmire
Description
The Quagmire group of periodic ciphers are similar to the Vigenère cipher but use one or more mixed alphabets. There are four variations; I, II, III and IV. The simplest of these, the Quagmire I cipher, is constructed from a keyed plaintext alphabet created from the keyword with repeated letters being omitted and followed by the unused letters of the alphabet in alphabetic order. For example the keyword PAULBRANDT is reduced to PAULBRNDT when repeated letters are removed. Appending unused alphabet letters produces the following keyed alphabet:
PAULBRNDTCEFGHIJKMOQSVWXYZ
A straight (A-Z) alphabet is used for the ciphertext alphabets. An indicator keyword is used to determine the period and alignment for the ciphertext alphabets. The indicator keyword is usually positioned under the A of the plaintext alphabet though it can be set under any letter. Creating a table using the indicator keyword BRANDT and the indicator position under A produces the following table:
*
Keyed pt paulbrndtcefghijkmoqsvwxyz
B 1 ABCDEFGHIJKLMNOPQRSTUVWXYZ
R 2 QRSTUVWXYZABCDEFGHIJKLMNOP
A 3 ZABCDEFGHIJKLMNOPQRSTUVWXY
N 4 MNOPQRSTUVWXYZABCDEFGHIJKL
D 5 CDEFGHIJKLMNOPQRSTUVWXYZAB
T 6 STUVWXYZABCDEFGHIJKLMNOPQR
The plaintext is divided into groups of indicator keyword length. The 1st letter of each group is enciphered from the 1st ciphertext alphabet, the 2nd letter of each group is enciphered from the 2nd ciphertext alphabet and so on to the end of the cipher.
Cipher alphabet: 123456 123456 123456 123456 123456 123456 123456 123456 ...
Plaintext: dontle tanyon etelly outhes kyisth elimit whenth ereare ...
Locate the 1st plaintext letter d in the straight alphabet and below it in ciphertext alphabet 1 is the 1st ciphertext letter H. Next the 2nd plaintext letter is o and below it in ciphertext alphabet 2 is the 2nd ciphertext letter I. Completing the process results in the following ciphertext:
Ciphertext: HIFUFCIRFKUYKYJPFQSSHZMMQONGKFKTNDQAWDJSKFKVJNHCLIRUCXOWHGUYIDJDUKG
The Quagmires 2, 3 and 4 are constructed in a similar way except:
Quagmire 2 uses a straight (A-Z) alphabet for the plaintext and a keyed alphabet for the ciphertext,
Quagmire 3 uses a keyed alphabet for the plaintext and the same keyed alphabet for the ciphertext,
Quagmire 4 uses a keyed alphabet for the plaintext and a different keyed alphabet for the ciphertext.
Examples
Type: Quagmire 1
Plaintext keyword: PAULBRANDT
Indicator keyword: BRANDT
Indicator position: A
Encipher the following Paul Brandt quote "Don’t let anyone tell you the sky is the limit when there are footprints on the moon.” gives:
Plaintext: dontle tanyon etelly outhes kyisth elimit whenth ereare footpr intson themoo n
Ciphertext: HIFUFC IRFKUY KYJPFQ SSHZMM QONGKF KTNDQA WDJSKF KVJNHC LIRUCX OWHGUY IDJDUK G
Type: Quagmire 2
Ciphertext keyword: PAULBRANDT
Indicator keyword: BRANDT
Indicator position: C
Encipher the following Paul Brandt quote "Don’t let anyone tell you the sky is the limit when there are footprints on the moon.” gives:
Plaintext: dontle tanyon etelly outhes kyisth elimit whenth ereare footpr intson themoo n
Ciphertext: RMGXKE VLGUQQ NWLJKB KXOFCY GADWYH NIDKHZ YELMYH NSLBWE DMHXSX EKOWQQ VELKQS J
Type: Quagmire 3
Plain/Ciphertext keywords: PAULBRANDT
Indicator keyword: BRANDT
Indicator position: P
Encipher the following Paul Brandt quote "Don’t let anyone tell you the sky is the limit when there are footprints on the moon.” gives:
Plaintext: dontle tanyon etelly outhes kyisth elimit whenth ereare footpr intson themoo n
Ciphertext: FXDIEO GNDBZI IHFCEN WDCQMU SLJPJV ITJXVK POFGJV IEFDGO JXQIDH OFCPZI GOFXZP E
Type: Quagmire 4
Plaintext keyword: PAULBRANDT
Ciphertext keyword: BRANDT
Indicator keyword: COUNTRY
Indicator position: P
Encipher the following Paul Brandt quote "Don’t let anyone tell you the sky is the limit when there are footprints on the moon.” gives:
Plaintext: dontlet anyonet ellyout heskyis thelimi twhenth erearef ootprin tsonthe moon
Ciphertext: KFBIFIC EWQVIIC OSXRXNC SBLSNMQ LNDCSQJ LJEKIGI OVDDHIG YFANHMD LHJGKLF XFJG
Solving
Solving methods:
Quagmire 1-3 - Hill Climbing and Dictionary keyword search.
Quagmire 4 - Hill Climbing search.
The Quagmires 1-4 cipher types require a tip for the solving routine. On selecting the Solve cipher icon the dialog box below will appear to enable the cipher period, tip and tip location to be set. On selecting OK the program will then search for a solution.
Cipher period – Set the cipher period from the drop-down menu. The range of values listed is set in the Limits on keyword range in the Options window.
Tip – Enter the tip in the Tip field. Spaces and punctuation will be ignored.
Click on the Locate tip button to populate the Tip location list with possible locations for the tip.
Tip location – Select the location of the tip from the list then press OK. When a tip location is selected the ciphertext and plaintext positions are shown below the Tip location.
If the Quagmire cipher is rerun the previous settings for the cipher period and tip will be displayed.
