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REF ID:A~148861' 

WAR Dl.PARTMENT 

OFFICE OF THE CHl~F $10HAL OFFICER 

WASHINGTON 

28 November, 1919 

My dear Coionel Eabyan: 

Your letter of November 17th has just. 

reached me dw to tile fact that you had the letter 

adcb'eaaed to 1202 - 16th street, N. w., instead of 

my present address, 172& Conneoti."cut Avenue, N. w. 

Wednesday I received and shipped to 

you two of the tubes you desired, with the understandiDg, 

of course, tha. t thee e are simply loamd far governmmt 

e.:xperimental iJurpoaes. The patent situation on these _ 

confolmded tubes is such tha. t ·we have to be very caretul -

that they do not get into unauthorised hands. 'Buff 

said. 

Your BE!COnd pal"agra.pb \18.S typically 

"Fabyan." You lmow I never have admi~ed that ,you bad 

any method for solving this cipher, and, as in the oaae 

of all the~e academic debates, you wi_ll have ~o pt'()_duc_e the pi-OOf'!)! I am sorry that I oazmot get a abanae to ~---- -

watch your work .as it goes because no dOubt you have 

perhaps reached other mathoda ot susgested attack thl\n 

those you have already described. Bo doub.t you ~ve 

tried and discarded what m1ght, perhap1, have some 

bearing on other wark. As you recognise, the by-producu of thia'investigation are highly worth while even 

thoggh there never was, 88 there never will be, a real 

solution. 

-- However, don't let me cliscourage you from 

making ,any 'further attempt on this cipher. In feot, I 

wan1i to encourage you, ao 1 am goiDg to clo ~hat you 

ask a to do in your last paragraph, tha~ 18, produ~ 

som more tapes of the s&1111 "confounde4 mean variety as the 

laat onea, which, h°"9ver, you fl:l'EI lnfor11Sd are not 

acoordhig _to What the Signal Carps ha.a been advised ,to 

use as standard :i;raotice. That ls, we are not going to 

introcluoe tbe feature ot ooding the key settings. we 

wlll give you J~st as we dld before, meaaages enolpher~d. 

in aooordaIIOe w1 th the letter at ins~otion of which you 

have a OOPJ• I suppose 1ou wlll want about another l . 

J !\pproved for Release by NSA on 11-18-2014 

I-, • . pursuantto E.O. 1352~1 ~ 11 .. -...;. .......... 

. \ 

/ 

/ 

WAR O~PARTMC'NT 

OF .. ICI: OF TH It CHIEF SIGNAL o .. .-JCER 

WABHJHQTON 

-~ 

hundred 118S11&.gea, .and as soon. 88 the officer-in-oha.rge 

of t.be system gets baok from New York CHy, which will 

be Monday, we will ~tart on the work of fixing up 

these 11Sssages in our spare time. I think tila t wl th out 

doubt these meaaages will reach yo·u wl thin two weeks because there isn't quite as moh siare time in whiOh to 

prepare them as we would lilla. 

W~th referenoe to this cipher, you, 

of oourae, know that it 1s quite possible to use only one 

of the two transmlttera, in o~r words, only one cipher 

' tape ot such legth that it will never :epea t itself. 

This ciplmr tape oan be prepared tl'om letters ahosen at 

random &J'.ld I am ~ather CU!'ious to know what yaur force 

has to say about the use of 1111oh a ~ whioh will not • 

r•B1llt in~ sort of a cycle such as ,given by,1

tl:le 

ad~itl_OJ1_~t ~_or ~ee _ar _more ol~er' tapes • ." _A few __ 

words about ~at they think of the possib..ilitiea of . 

deoipherlng the mesas.gee enciphered by this method will 

be of in'terest. · A • 

With warmest regarda,. 

. . 

~olonel Geo~ PabJBD, 

Blv•~banlt ~boratozlea, 

Geneva, Illliioia