In presentations to groups with crypto interests, I begin my talks with a bit of cryptology history and lore, citing the age-old battle of wits between the cryptographer and the cryptanalyst. As one cipher system was developed to mask the high frequency letters, a cryptanalyst would go to work at removing the mask.
The Ragbaby, a poly-alphabetic substitution cipher with a systematic progressive key, was developed in the early 1950’s by ACA member, SHERLAC, as a means to disguise high frequency letters and further the security of secret messages.
Before we stretch our mental capacity in wonderment at the Ragbaby deciphering principles, let’s look first at its construction routine that serves as its foundation.
Discussion of the Ragbaby Cipher provides us with an excellent opportunity to re-state one of our most basic solving axioms. The unarguably most beneficial aid to the success of mastering a cipher solving process is the understanding of its construction process.
24 Letter Keyed Alphabet – Keyword, CIPHER
Encipherment is performed with word divisions intact and a 1 to 24 numbering system is assigned to the plaintext letters. A 24-letter keyed alphabet, traditionally paring the letters I/J and W/X, is used to convert plaintext to ciphertext.
CIPHERABDFGKLMNOQSTUVWYZ J X
The numbers are interrupted with each word division as the next number in sequence begins each new word. Ciphertext is then assigned by selecting the letter representing the sequential number of spaces to the right of the plaintext letter in the keyword alphabet. A “picture” is worth a thousand words:
pt: Now is the time for all good men.. #: 123 23 345 4567 567 678 7890 890 CT: OSC HV WBF YAUK NWL LUV SZCT WMC
Number each remaining letter in a word by counting up from the number of the first letter in a word. Ciphertext is written, as above, with word divisions intact. A hyphenated word or one with an apostrophe is considered a single word and the numbering system continues across the hyphen or apostrophe.
The counting to encipher plaintext “Now” to ciphertext OSC” is shown below.
CIPHERABDFGKLMNOQSTUVWYZ >1 >12 3 >12
Keep in mind that I/J and W/X share the same position in the 24-letter Ragbaby ciphertext alphabet. These couplets are counted as one in the shift of letter spaces between plaintext and ciphertext letters.
A 1 to 24 numbering system is continued throughout the encipherment of the plaintext. Each new word continues the numbering sequence with the next highest number. When the number 24 has been reached, the numbering sequence restarts with 1. Since 24 will result in identical plaintext and ciphertext letters, this is often a good entry point into the cipher’s placement. The preserving of word divisions in the ciphertext also allows cipher crib placement by the counting of word letters. Crib placement is also aided with the retention of punctuation in the ciphertext.
Let’s reverse the enciphering process to decipher a Ragbaby Cipher.
R-1. JF2007. Unbalanced arguments. (because) ANGO-KA
YBWHC OD QDAM GT: GMTQT YEG LKHY RRSL KP DPLB UQMQT KP PUC EPBU RVDT ZURV YPBVNIU PCY TAT’A DYRD Y HDG UO SITEH ND.
Word divisions and punctuation are all in place, including an apostrophe, a colon and some very short words that will all help us in the encipherment process. Using our construction principles as a guide, we know that our first step in the decipherment process will be to number the ciphertext letters. These numbers indicate the ciphertext letter location relative to the plaintext letter it represents in the Keyword Alphabet. 1Y indicates that CT letter Y sits one letter to the right of its plaintext letter representative.
Numerical Sequencing
11 12345 23 3456 45 56789 678 7890 8901 YBWHC OD QDAM GT: GMTQT YEG LKHY RRSL 1 1111 11111 11 111 1111 1111 1111222 90 0123 12345 23 345 4567 5678 6789012 KP DPLB UQMQT KP PUC EPBU RVDT ZURVYPB because 1112 112 122 2 2222 2 222 22 2 7890 890 901 2 0123 1 234 34 41234 12 VNIU PCY TAT’A DYRD Y HDG UO SITEH ND. g o s
Encipherment uses a keyword alphabet to select cipher- text letters 1-24 spaces to the right of the plaintext letters they represent. Decipherment will reverse this procedure and select letters to the left of the ciphertext letters to determine the plaintext message.
Whenever a twenty-four appears above a ciphertext (CT) letter, the plaintext (pt) letter will be the same letter as the ciphertext letter. In a Ragbaby cipher, a letter may represent itself. (Self-encryption)
Crib Placement
Our benevolent constructor has used only one word in the message that is seven letters long. Crib placement is simply a matter of matching the crib to the seven- letter ciphertext word. We have inserted the crib “because” along with the plaintext letters, g, o and s, which are 24 letters away from the ciphertext letters in the key alphabet.
Keyword Alphabet Letter Placement
We will use our crib placement and numerical sequencing to aid us in our recovery of the keyword. We begin with the identification of the 1 to 24 numerical sequence at the top of our table and compute the number of alphabet spaces separating the crib pt from its CT letters.
2 2 2 2 2 1 1 1 1 1 1 1 1 1 1 9 8 7 6 5 4 3 2 1 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0 b Z e U c R a V u Y s P e B U B E Y Z 2 2 2 2 2 1 1 1 1 1 1 1 1 1 1 9 8 7 6 5 4 3 2 1 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0
We post those letters with the known spaces between the pt and CT letters in the key alphabet. B is 16 to the left of Z; E, 22 left of B; E, 17 left of B; U, 21 left of Y We can now return to the cipher construction and identify pt letters in the message by using the key alphabet letters and the number of spaces between the pt and CT letters.
Example: The letter E appears 17 spaces to the left of letter U, thus U17 = e. U appears 20 to the left of letter Y, so Y20 = u. B appears 16 left of letter Z, so Z16 = b.
Plaintext Recovery Process
In our Ragbaby enciphering process, we placed our crib in the plaintext, along with the plaintext letters g, o and s, three letters that are 24 places away from the ciphertext letter, consequently sharing the same plaintext (pt) letter and ciphertext (CT) letter.
Ragbaby solving procedure reverses its construction process, identifying pt letters by their location to the left of the ciphertext letters. CT, 16Z = pt, “b” because of its location, 16 spaces to the left of CT Z in the key- word alphabet. (See keyword alphabet.)
11 12345 23 3456 45 56789 678 7890 8901 YBWHC OD QDAM GT: GMTQT YEG LKHY RRSL 1 1111 11111 11 111 1111 1111 1111222 90 0123 12345 23 345 4567 5678 6789012 KP DPLB UQMQT KP PUC EPBU RVDT ZURVYPB e because 1112 112 122 2 2222 2 222 22 2 7890 890 901 2 0123 1 234 34 41234 12 VNIU PCY TAT’A DYRD Y HDG UO SITEH ND. you t a g o s
Plaintext recovery is aided by short words “a” & “to” (2) as well as a punctuation mark (apostrophe in this one is a “t “or “s”). Plaintext recovery of “you, a and apostrophe t” adds to our keyword alphabet.
Keyword Alphabet
Our keyword alphabet now looks like this.
C A U T O B E Y Z 2 2 2 2 2 1 1 1 1 1 1 1 1 1 1 9 8 7 6 5 4 3 2 1 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0
A good case can be made for the keyword of “caution” which would generate the following completed keyword alphabet.
C A U T I O N B D E F G H K L M P Q R S V W Y Z 2 2 2 2 2 1 1 1 1 1 1 1 1 1 1 9 8 7 6 5 4 3 2 1 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0
We use this completed keyword alphabet to fill in the remainder of our JF07 Ragbaby plaintext, locating those pt letters the noted spaces to the left of the ciphertext letters in the cipher.
JF07. Unbalanced arguments. (because) ANGO-KA
1 11 12345 23 3456 45 56789 678 7890 8901 YBWHC OD QDAM GT: GMTQT YEG LKHY RRSL Words to live by: Never put both feet 1 1111 11111 11 111 1111 1111 1111222 90 0123 12345 23 345 4567 5678 6789012 KP DPLB UQMQT KP PUC EPBU RVDT ZURVYPB in your mouth at the same time because 1112 112 122 2 2222 2 222 22 2 7890 890 901 2 0123 1 234 34 41234 12 VNIU PCY TAT’A DYRD Y HDG UO SITEH ND. then you don’t have a leg to stand on.
Follow the ciphertext conversion to plaintext, beginning with the plaintext beginning, “Words.” Pt “W” is one to the left of CT “Y,” “o” is two to the left of “B,” “r” is three to the left of “W,” “d” is four to the left of “H” and “s” is five to the left of “C.”
As in all decipherment processes, the key is the charm that allows us to read the secret message. Attack the Ragbaby key with proper crib placement, short word analysis; word guesstimates based on the cipher title and the ever-present watch for that common trigraph “the.” This cipher makes ample usage of the “senorita” letters and common digraphs and trigraphs. Ragbaby constructors feel less of a need to alter the general properties of letters.
R-1. JF 1999 Cm. Marital Bliss. (TBWNWFP = parents) LIONEL
PE TBWNWFP QLK LV YASAQ EGDU USHKQAM DGATRCC. EEG LFLVCB’V GNBLC MSN EAML AM GUF MEHEE VDT AZI QVQIYN’I WONQY EYQ UGEQ GE WTV UPDKZ.
R-2. MA2011 Cm. Change is recommended. (perfect) MARSHEN
YBED CST YOVYTP EFCSKSV SGDK MUKGN OGVMW NL MQAIPC WLL GTV AQ ZS; KP GVIH NF WCV LMZR AIMB PHPTGK SO’C KVVAV LEAG TKB QBI.
R-3. JF 2012 Cm. Premature. (before it) WORD WIZARD
FQCGZOIW PAMI NBECK DROTL PVK WMAH LUN GEBUP ZSNAGMP BL UFPZ NUVCIAQFA FPT CIEE DISIHP LL ZNDIY TFYQZLG. *TBTHKIO *WWHKEV