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COPY NO. 12 

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J/SC 66/4 

13 December 1949 

JOINT COMMUNICATIONS-ELECTRONICS COMMITTEE 

$ECURITY AND CRYPI'OGRAPHIC PANEL 

REPLACEMENT OF THE PRESENT COMBINED CIPHER MACHINE 

Note bJ _the_Secretary 

1. The enclosure, a report or th~ Join~ S~curity and Cryptographic Panel is forwarded to the Joint Coordinating Panel for 

consideration and ls circulated to the members of the J/SC Panel 

for information. 

1'0P 5!0R£1J! 

W, R. JOY 

Secretary, Joint Security and Cryptographic Panel 

J(~C 66/4 

C_Ji P Y 

Declassified and approved for release by NSA on 09-20-2013 pursuantto E .0. 1352\3~ 

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RE~ORT BY THE JOINT COMMUNICATIONS-ELECTRONICS COMMITTEE . ' . . 

to the 

.J'OINT CHIEFS OF s·TAFF 

.Q.ll 

!Y'PLACEMENT OF THE PRESENT COMBTNF'D CIPHER MACHINE 

THE PROBLEM 

1. To comment and make recommendations on the memorandum from 

the British Chiefs of Staff (RDC 1/36, dated 5 December 1949, 

• enclosure to JCS 20?4/1 1 dated 6 December 1949) on the replacement . . of the present Combined Cipher Machine ( CCM). 

FACTS BEARING ON THE PROBLEM AND DISCUSSION . ' s . 

2. See Enclosure "B". 

CONCLUSIONS 

3. It is concluded that: 

~· Complete interchange of cryptographic principles should not 

be ~pproved without qualification, but that a limtted agreement in 

certain fi~lds should be proposed. 

b~ The U.K. s~ould be invited to:disolose the new British 

Cipher Machine to the U.S., as the basis of adaptation to a new 

Com!.'>l.ned Cipher Machine which would link. together the new British 

Qtpher Mac_hine and t_he appropriat• U. S Cipher Machine. 

~- The U. S should agree that attempts be made to develop a 

7-rotor BCM as one of the possible replacements for the present CCM 

Howevr-r no definite commitment should be made as to the adaptation of 

the ?-rotor BCM until the U.S. is satisfied with the development. 

d. The British propsal of a 7-rotor ECM should not be 

accepted. 

~· Combined U.S -U.K. communications should continue in the 

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:t'¥.esent CCM until an emergency, or until such ttme as a new.com.-

bined c~.pher machine is available and fiCCepted. Such improvements 

as increasing the number of rotors to a ~et, frequent eupersesslon 

of rot-ors and ltey lists, lnterchangeabl~ cam cop.tours, and any 

o~her feasible material improvements should be introduced. 

r. The U. S. should assure the U.K. that, in the event of an~~~~~~~~ 

_emergency before the completion of the new combined cipher 

~achine, the U. $. will furnish to the u. K. a limited number of 

U. S. cipher machines to meet immediate urgent needs of highest 

command communicattons. 

RECOMMENDATIONS 

4. It is recommended that tP.e memorandum in Enclosure 11 A11 be 

torwarded to the Representatives of the British Chiefs of Staff. 

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TOi ijiC~iT .ENCLOSURE 

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"A" 

P .RA F T 

MEMORANDUM FOR THE REPRESENTATIVES OF THE BRITISH CHIEFS OF STAFF ... :;;· 

· 1. The U.S. Chiefs of Staff have considered the proposals made'in . . . .· 

RDC 1/36 of 5 December 1949 concerning the replacement of the present 

Combined Cipher Machine (CCM). The two requests contatned in paragraph 

7 of RDO 1/36 are discussed herein in turn . 

.§.· W.htch c lE?er mechan tam should b.e employed on a longterm 'bas ts within the Comb1ined Ctpher Machine: 

Should the British Chiefs ot Staff care to disclose thetr new 

cipher machine as the b~sts of a possible new combtned cipher machine, 

the U. S. Chiefs of Staff will be pleased to consider this machine for 

such adaptation of both the U. S and U. K. destgns as may be feasible 

to.provide intercommunication. 

·However the U. S. Chiefs of Staff consider that the ?-rotor BCM .. 

mechanism with appropriate stepping provides adequate long-term security 

for combined communications and therefore recommend that the British 

machine be comp~eted with this in mind. Thts 1s 'desirable in order that 

in the event the U. S. 7-rotor BOM development becomes satisfactory this 

mechantsm might be an alternative replacemen~ for the present Combtned 

Cipher Machine. ; . " 

b. 

-- The interchange of cryotographic principles on a 

rec12rocal-basis: ~ . .. . . ... 

. ·The U. S. Chiefa of Staff regret that they are still unable to 

accept such a proposal without qualification. Howevf_3r, the U. S • 

. Chiefs of Staff reQognize_ that, in certa~n fields, such interchange may . . 

be very profitable to both the U. S. and the U.K_., and are agreeable 

to m~iing this the subject of a conference- in Washington. 

2. The U. S. Chief of Staft are in agreement that the potential 

insecurity of the COM can be reduced in part by additional rotors in 

the set and by the ultimate addition of inte.rchangealHe tires bearing 

the stepping_oontrol notches, and that ever~ effort should be made in ,· - . . 

these directions until the successor machine to the CCM is available 

for combined communications. 

In this connectton, in the event of an e~ergency before the com 

-3- Enclosure 11A11 

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pletion or the· new combined cipher machine, the U. s. Chiefs of Staff 

assure the British Chtefs of Starr that every effort wlll be made to 

provide the U.K. with a limited number of U. S. cipher machines to 

meet immtdtate urgent needs of htghest command communtcattons. 

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ENCLOSURE 11B11 

. ,_ 

FACTS BEARING ON THE PROBLEM AND DISCUSSION 

l. The U.K. has, for various reasons, rejected a proposal of the 

U. S. (Enclosure "A" to_ JCS 2074, dated 18 October 1949) to adopt the 

6-rotor BCM for combined use. 

2. The JCEC has re-exam1ned the problem, particularly centering 

its deliberations around paragraph ? of the Appendix to JCS 2074/1 

which raises three ne~ possibilittee for combined cipher communications, as follows: 

a. The 7-rotor.ECM 

b. The 7-rotor BOM 

c. Both the ?-rotor EOM and the ?-rotor BCM at different 

communication levels. 

3. With regard to the proposal made in paragraph 2,!l above, that . ls, the ?-rotor ECM, there is no such machine now in existence. The 

·-

u. s cannot_ afford, from an operational ahd economic viewpoint, to 

consider _produ61ng such a machine. To do so would entail a shift 

from the yresent NCM-CSP 2900 program to whtch the U.S. is firmly 

committed. ·In fact, the U. S. Navy will commence use of the CSP-2900 

as o:r 1 July 1950; the Army and Air Force will commence using this 

machine as soon thereafter as their produa".tion requirements are met. 

4. With regard to the proposal made in paragraph 2b. above, i.e., 

the 7-r~tor BCM, it is probably feasible, from both cryptographic 

and engineering standpoints to produce an adaptor to the NCM-CSP 2900 

machine, which would permtt ?-rotor BCM combined commun1cat1ons. . . However, in order to assure combined communications to all U. S. 

commands, tt would be necessary for the U. S. to provide a separate 

7-rotor BOM for use in sens~tive or semi-sensitive areas because just 

as the U.S. does not in peace time expose the ECM in such areas 

netther should the U. 6. expo~e the CSP-2900. 

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-5- Enclosure 11 B11 
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5. A ?-rotor BC!j would pro·vide vastly more secure combined communications than either the CCM or the present 5-rotor BCM. The 7-rotor 

BCM should have security comparable to that or the ECM. This point 

cannot be established definitely until all cryptographic details of 

~he. 7-rotor BCM have been determ tned and appropriate security studies 

have been conducted. 

6. With regard to the proposal made in paragraph 2~. above, i.e., 

both the 7-rotor ECM and the 7-rotor BCM at different communication 

levels, this proposal must be discarded in view of the facts stated 

in pa."ragraph 3 above. 

? . a. Th~ __ !!ecuri ty evaluation of the 5-rotor BCM dlade in the 

Appendix to JCS 20?4/l is substantlally correct~ but it implies that 

the evaluation is also applicable to the present ECM. It is certain 

that ·the application of the proposed British attach to the ECM is 

very much more complex and difficult. 

b. Although the U. S. security experts agree that the evaluation ts substantially correct with regard to the present 5-rotor BCM, 

it should be noted that the solution le based on the assumptton that 

the rotors are physically compromised. Considering the care and ex-

·pense that are taken in produding, shipping, and. accounting for 

cryptographic material, the routine acceptance of a presumption that 

the rotors for a ctpher machine must always be constdered compromised 

appears to be considerably beyond the normal limits of calculated 

risk. Indeed, if it must be assumed that the rotors are always 

compromised, then there is no valid reason for not assuming that the 

key-lists are also always compromised. 

( 1) Further, the presumption co_ncerning the 25-letter 11 crib11 

assumed that the crib is correctly placed tn cipher message, 

and all time estt~ates of the soltuion are based on this 

-assumption. As a matter of fact, both the U. S. and U.K., 

use two special encryption techniques, btsection and variable 

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Enclosure 11 B11 

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·spao:tng, speo:t:f' lcally des:tgned to h:tn_der. orib-f_1 tt1ng; 

they are very effective for that purpose_ • 

.2.· Increasing the number of rotors in a COM or BCM set from 

10 rotors to 20 rotors wQuld tncrease the length of time a 

hundred fold. 

d. The introduction of rotors wi~h interchangeable CBJ'.ll 

contours, and more frequent supersession or rotors and key iists 

in conjunction with an increased n~mber of rotors to a set can 

make the security of the prPsent CCM acceptable for a considerable 

. period of time (at least five years) 

8. The second Part of the U.K.'e proposal, to effect complete 

interchange of cryptographic principles on a rectprocal basts, 1s 

still considered unacceptable unless qualified. However, certain 

limited tntercnange may be profitable to the U.S particularly in 

the following communication fields: ·. 

a. non:..l:tteral 

b. low echelon literal 

o. met_eor_ologioal 

d. merchant ships· .. 

-g. This study has been coordtnated with tne Armed Forces Security 

Ag~n~y Cou~cil (AFSA). 

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