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SUMMARY 

1. Pursua,nt to' verbal ahtho.rit;r, '.·d~~~s~ib~:~~~~_;liellf~~~"~~~;~:::-_ c·:o-~::~: ~:' with representatives of the British Governmerit on ue· ila~ter 

of improving the sectirity of the Combined Cipher :Machine. The 

results of the conferences as agreed upon by British and U.S. 

representatives are as set forth in.Tab A. Although a det'init-e 

agreement was not reached, ·a .fip basis therefor was established. E==-j.s . 

2. The following ~tlin~s the pres~ritati~k~'DiiAa b,. ·the· - -~ ~-·. ·\~'~tl~~~ Britieh representatives at the opening meeting: 

a. In the opinion of the British, th~ :pretient Comb:lnecf 

Cipher Machine (CCM) is not sufficiently secure to resist increasingly effective cryptanalytic techniques. In addition, 

the British are anxious to develop a replacement for their present high level cipher machine_ (Typex). 

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b. For reasons of economy the British feel it desir.: -· · · 

able that any new intra-service machine developed b.Y. them be 

adaptable for Com~ined use and for this reason they are anxious · 

to participate in parallel research and development with the U.S. 

c •. The British indicated that they were aware ·or the' j 

principles of the high grade U.S. cipher machlne, SIGABA (ECM). / 

They described this equipment quite accurately, considered its / 

security to be of the highest order, and stated, in fact, that 1 they had incorporated its principles in a radioteletype cipher I 

machine for their own u·se. \ 

d. · The British stated that they had developed an idea 

which they termed as "nay; and revolutionary" wr.ich they feel 

is superior to the SIGABA principle. They fUrther indicated ~ '~ l ;~- .,~ ~ ~?' .-T 

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-e-c-la_s_s ..... ifi_e_d_a_n_d_a __ ro_v_e_d_f_o_r_re-le_a_s_e_b_N"""'"S_A_o_n ___ o ...... g_ ..... ·2 .... 0-~~ ..... o--· 1-3--u-rs_u_a_n_t t-o-E ............ 0 ....... -1""""3""""5""""2 ..... Q""c_ 1 ~ 
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that ~ the U.S. were willing to consider the eventual replace-

.. ment of the SIGABA with something more secure, they ~oulc like 

to ma.Jee available their new principle for a cipher machine 

'. which could be used for Combined as well as intra-service 

. .. cOllUlltllii~ations. If, however, the U.S. did not contemplate 

·.' replacement of the SIGABA, the disclosure of their new ideas 

;, "ttotild be only· of academic ·interest. In the latter case, the 

' ·-·:!t · · .::-~\... 1 )h'if,ish suggested that the SIGABA principle be incorporated in 

: ._."~~'i. ~~:t . a nn COM, which principle they wOUld also incorporate in their ... ~.:. i:':.: · ;-1.ntra-service machine. 

r).~:tf~--. ..,.~~ j. a. It has been U.S. policy to withhold the cryptographic 

; ·, ~j . ··.'.~:- • <pr,inci,p+e of the SIGABA from 8.11 foreign powers, including the 

f. .. '.-?~~_- .. ~::_f;,"-.,/· :~Briti.sb.1 . Therefore, in spite of obvious British knov-;ledge of. ~- _:';? ··~·:._ '. · 'th.e pr~ciple ·of this device, discussions were temporarily 

~ · .. ~\~:··i<,,;·~:· . ·di;scontinued ~ order that the U.S. policy could be reexamined ~ - ::-.-..~·:i:·~i:',-: :··in j-oliit session. · :_~·- >-~ ~- ~t··· -~ -~~L:~.·.·· ~ _,.~ .. _ . '.. ··. -. . 

~- ),~·; ~~;;..~:./~·.: <• • i ·~ b. .At the joint conferences, the Army representatives 

:. >:.~ »;{°~·-::-: ~ ·_Jtpolc_-the position that they could see definite advantages and 

i ~-~'.~~- ~::~i ··~ , ' nc>.·aeriOQ.s disadvantages to the U .s. in the release of the 

;. , _ ~ .'.:'t'~- .·. "'. ;_ .,f!~GABA. principle !"or incorporation in a new Combined Cipher :-,~c \; ~~: ·:!.;£ ·:· _'-'.. iJlaehin,i!I, and in view of the circumstances, were desirous of 

~-:· ~:::j drl" ·[ .; ' . :rec9mnt"itliding' to higher authority the reconsideration of the 

~-. :~- ~;;~~ t ·· · eXIBt!ng policy 0£ non-disclosure of the SIGABA principle. 

~.:_·:·''!':~;; ·:~ .•--.H~e;r, i~~Q serious ob~ctions on the part o~ ~ .... -~}~~~· }~~:r..eR.resentati~ep, it was finally jointly agreed to 

l, -:=:;;~-t.~~-- r~· ; -~ol'll_,}he British that the SIGABA principle could not be dis-

~£; :~~~3~:~_- ·~:.;/~;: Cli..88.ed~ As a result, _that_ phase of the matter was completely 

~~· · .,_~<i::t· _).:._:; e:llntl~ted tr0m discussion during subsequent Combined meetings. 

~-~··:~1i~f4r>~·>c.· ';»'J Upon receipt of th~ dec~sion indicated above·, the 

~ ,{>'.~£~1-;~f :.:'~1ti8! representatives made a complete disclosure of their 

k~·::.----~{'.~~i't;..;J~;~f1$1(:~ revolutionary• idea. The U.S. representatives wer~ 

. ;;.'-::'~~~r_;j~'lriiab~~-;to 8.c.c-ept it_ due t()_ engineering and maintenance difficul-

. -~L;~~~";:~-:,,f~-~~Jes ihi~h,, inJ.heir cQpsidered opinion,_ would make a device 

, .· _ -~ ·-:.3."~: ~ ;~,i;~Qas~ ~ere.on. impra.Cti~al~_ . The British representatives, in ~. '·j}~;-~~-~:·;~~f-pJ.:te~f _this' ad..jerse opirilon, stated that they expect to con-

". ·.~?~-' ·~..cti~{';.ltixm~~c!evelopment ot equipment, incorporating these principles 

' -~:~~=~~,_;:;~:':a-dl"t"tnlicaied that the resUlts of their work would be made 

:~ :'~~"-;~_~-7~~~.J~i~li.l>'le to the U.S.,· ti~in _the_ir view it might have Combined 

;~_ ~:3fi\~~~-~~~P!?mtti~~·· ~; > >.; -~ ~~ . ~·~:< ... : : . . : . · . ~: ;;~~\~~.-~;:~b-< ,.,-f$i: TheJf.S. ·representatives then presented their olln 

r'~ ~-~"~~:;~L>~~~:i ~or the,~μlpri:ivement :or t'\le security Of· tlte" Combined Cipher .'.'-· _ -~:;-... '"'< ·~:ut~'B!De:~· ·These. ideas witl .. be studied by- the British from the . 

~ :::.~·:k~ ~"_o:~~~mi,i)~nt.'· o~ crrr,obo'r~l~F.£.the_ u.s.' estimate of _enhanced 

.. -,_~-~~~-,~·::r;;-;~~~· __ At the_ .~e ...,t.iJI!,~, ,.:the U.S. will co~tinue its research 

"-;;;'~-"':.-:~-·Jtr~.~~.:~l~~!~ ot_ P;!lc_tfoal, or engineering and maintenance, 

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REF ID:A2435927 

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problems introduced by the proposed changes. These British 

and U.S. studies will require approximate.lJ' three months and 

ai'ter study of the results by all concerned, it should be 

possibee to reach a definite conclusion in a total of six 

months. 

6. a. The British representatives indicated their desire 

to collaborate in the development of a cipher machine for 

Combined use in lower echelons; however, the U.S. representat~vea lacked authority to enter into such discussion. The ~ British urged that the necessary auttority be requested. 

b. During the war just ended there was a need for 

such a.device. As a resuit of practical experience the British 

·are in a good poisition to contribute basically ne. and improved 

ideas to CI"Y,Ptographic projects, and it is therefore believed 

. that collaboration would be useful and advantageous to the U.S • 

. 7. As a preliminary.to fllrther collaboration, however, 

,the U.S. representatives proposed that Combined Communication Secu~ity Regulations be established in order to standardize 

· the protection afforded combined cryptographic material, This . propo'sal was taken under ~dviseptent by the British, who will 

prepare a draft set of regulations. Both the British and the 

U.S. will subm~t their re~pective drafts to the Combined ~ommunications board in order to obtain a.mutually acceptable 

84.t of combined regfllations. 

RECCMMENDATIO.N • 1 · 

· It is recommended that contingent upon the establishment · of a set of Combined. Communication Security Regulations and 

subject to concurrence or the U.S. Navy, authority- be granted 

to collaborate with the Britishi (a) In the improvement of 

the Combined Cipher Machine, and (b) In the development of a 

low echelon cipher machine for combined use. .. ' . ·. · .. ·"' 1 · .. ,, 

· .Approved 2 May 1947 by order of the Secretary of War, 

THOS. T. HANDY, Deputy Chief of Sta£f, •subject to clearance with SWNCC and •itbin. 

present budgetary and manpower limitations." 

/s/ Walter E. Todd 

WALTER E. TODD 

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/a/ Victor L. Cary 

for- I. E. Thurman 

Lt. Col C.SC Asst to the Deputy Chie!' 

of Staf .f 

Brigadier General, U.S.A. 

-Deputy Director of 

Intelligence 

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