Paul Rubin’s cipher, revisited…

Back in 2015, I blogged about the ciphertext that was found taped to Paul Rubin’s stomach, and also wondered whether Rubin might have suffered from paranoid schizophrena, and whether the FBI would ever release his code-tables. On a larger scale, given that we only had a single scratchy newspaper photograph of his cipher to work with, it seemed that we were unlikely to make huge progress.

Well, a lot of that has now changed.

Craig Bauer’s “Unsolved!”

Craig Bauer’s (2017) “Unsolved!” covers a good number of cipher mysteries with a particular focus on Americana, and so his book covers the Paul Rubin case on pp.289-304. Very kindly, he passed me the following (much clearer) scan to work with, that his book had reproduced at a fairly small size:

Hence I’ve added a page on the Paul Rubin Cipher to the Cipher Foundation website: this also includes my transcription of the cipher, as well as (thanks to Albert Mock) a copy of Rubin’s death certificate and details of his grave.

Arguably even more importantly, however, Craig Bauer also received a 160-page document set from the FBI following a Freedom of Information Act request (though this arrived too late for him to use in his book), which is now also linked on the Cipher Foundation webpage – and this is where our real research begins.

Paul Rubin’s FBI File

A number of suggestions as to the possible contents of the cipher appear in the FBI file: that it might be written in cable language, that it might contain cribs for a chemistry examination, and so forth. It also lists (p.25) possibly the first nutty theory about the cipher, courtesy of Mrs L. Rohe Walker, 2 Beekman Place, New York 22, NY.

For me, though, one particularly interesting aspect of the file is that it details (on p.66) the specific sequence that the FBI’s cryptanalysts followed to try to understand Rubin’s ciphertext (though without success). It starts by listing the languages FBI linguists tried: “Yiddish, Hebrew, Russian, German, Hungarian, Finnish, Latinair [?], Lettuishuan [?], Turkish, Portuguese, Rumanian, Italian, Spanish, Dutch, Danish, Norwegian, Swedish, Malayan, Albanian.” They also “[t]ried to develop words phonetically and as abbreviations, with no success.”.

It then moves onto cryptanalysis, firstly listing the “Direct Cipher” methods they looked for (all with negative results):

a. Monoalphabetic Subst.
b. Transposition – uniliteral
c. Partial encipherment with & without nulls
d. Typewriter displacement
e. Combination subst + Transp + nulls + partial encipherment
f. Commercial word codes
g. False language
( 3 books from Library of Congress:
( * “On the Choice of a Common Language”
( * “Method [?] to Esperanto”
( * “A Planned Auxiliary Language”
h. Binary substitution as superencipherment

It then lists the “Open Codes” they looked for, firstly for letters mapped across the whole specimen:

(1) Constant key positions 2-25 (Entire specimen)
(2) 1st, 2nd, 3rd …. final letters of words, initial letters – forward and reversed alphabets
(3) Beginnings & endings of lines (+10 and -10 letters)
(4) Numerical key 7469921 as letter positions
(5) Capital letters, including letters to right & left

Next they looked for words embedded in the entire specimen:

(1) Constant key positions
Also 1st, 2nd letters of constant keyed words 2-10

They moved on to search for possible “Distorted Words”:

2PONT = Dupont
1/4ly = Quarterly
AS(GESTALT)VERBENSDI
KETELLE = Catelle (psychologist) ?

They also looked for possible names, cross-referencing them in the FBI files (e.g. for B. H. KETELLE):

TYWOOD-JANOSSEY-KETELLE [lists FBI document references]
IVAN DIOLON (negative)

Next, they list various observations made by the cryptanalysts. This for me is the most interesting part by far (note that ‘Q5’ is the reference names for this ciphertext within the bundle of evidence made available to the FBI):

1. Peculiar letter combinations of contacts.
a. Phonetic & pronounceable but unintelligible. Hebrew/Yiddish influence observable.
b. Doubled letters – with “KK” at beginning of one word.
c. “MN” digram, occurring 3 times at end of words.

2. General letter frequency:
A = 21, B = 5, C = 4, D = 11, E = 35, F = 3, G = 10, H = 6, I = 15, J = 1, K = 7, L = 23, M = 10
N = 21, O = 17, P = 3, Q = 1, R = 13, S = 12, T = 15, U = 5, V = 5, W = 3, X = 1, Y = 3, Z = 5
2 = 1

3. “Digits” at bottom of Q5 not in organized form. “X” and “.” appear haphazardly. Makes no sense in attempts to convert binary to digits.

CONCLUSIONS:
1. Letter frequencies and pronounceability indicate phonetic composition.
a. May be syllable, phonetic, or artificial word code. If so, material is insufficient for analysis.
b. letter material looks like irrational or unsystematic composition

2. Digits have irrational composition. Positions of “X” and “.” do not assist solution. Concentrated efforts on “Binary”, produced no significant results. If digit code on cipher underlying binary, material is insufficient.

Is It A Real Cipher?

On the one hand, the parents “did state, however, that there were a number of papers of a similar nature in their home in Brooklyn. They stated also […] that Benjamin Birnbaum […] would undoubtedly be able to furnish information concerning the ‘coded note.’ ” Later: “Mrs Rubin stated that her son and his friend, Benjamin Birnbaum, often exchanged “notes” similar to the one found taped to the subject’s abdomen when he was found.” (p.17). Yet “BIRNBAUM advised that he never sent to nor received a coded message from deceased” (p.29).

Rubin was also fascinated by binary. Birnbaum “stated that the deceased talked of using a word unit code with numbers for each word. The numbers would then be transmitted into the binary code. BIRNBAUM advised that the binary code is a code used on all calculating machines. He stated that the deceased was going to use another stage of transmitting this code unknown to BIRNBAUM.” (p.35)

I think it is abundantly clear from the file that Paul Rubin and Bernard Birnbaum did communicate by means of cipher, even if Birnbaum strenuously denied this under interview. Rubin and Birnbaum thought that everyone else was not only stupid, but deserved to be treated as stupid (and said so in the interview): so if Birnbaum treated the FBI as stupid, we should perhaps not be surprised.

In my opinion, the cipher would seem to be completely genuine and that Paul Rubin’s parents and Bernard Birnbaum did initially have access to Paul Rubin’s codebook. However, I strongly suspect that they chose to destroy it rather than give it to the government, lest the ciphertext reveal something unsavoury about the dead student’s end – better for him to die in mystery than in possible ignominy.