'":"STANDARD FORM NO. 14 

TO : 00'// r-c.s 

Thru · :d~. 04T, (!~ 

FROM :"fT4l2 

DATE: 15 June 1951 

SUBJECT: Telecrypto and Cryptex Model CI 

1. Inolosed here;vi th is a report "Brie£ Security Estimate ~f Telecrypto", 

as requested. 

2. -Also inclosed are coITl!!l.ents on Cryptex Model CI. 

3. Mr. Hagelin' s letter is returned herevri th. 

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Inclosures - 3 

1 - Brief Security Estimate of Telecrypto 

R. H. SHAl'J' 

Head, AFSA-412 

2 - Comments on Cryptex l·'odel CI ___ __ __l iJ~- ~ 7)f 

3 - Letter from l!r. Hagelin £th/er/ ..M, ~Lto~··'«U.. 'O S: 14~ 

Declassified and approved for release by NSA on 06-17-2014 pursuantto E .0. 1352a 

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am SECURITY ESTitTA'l'E OF TELECRYPTO 

APSJ.-f12B/egb 

15 Ju.ne 1951 

1. 'l'•l•erypto b a k•y ~nerator using the M-209 pin wheel a11ea'bl7 (which 

•t.P• u in 11•209), 4 k9Y oyl!nders and 12 ... bar drum. Th• key o:ylinden 

are st.pped erratically by the teeth on the 12 bara of' the drum. which in 

turn are 1lld by the intera.otion of the piius and luge. The eelaction ot 

which key cylinder ia to be u1e4 is controlled by a second reading position 

on 3 of the pin wheel.. , 

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2. A.FSA 4121' oonduatod A week'• 1ntenlliw ••aurity atudy ot 'leleorypto. 

This paper ii a. .unary of the reau.lt1 of that •tudy. 

s. Cryptographic ltequireaen.tl. 

a. Daily Key. - T•laemto haa,many variable• that sit be aet daily, 

thereby orea:ting many chances tor operator error. !he 1ystem11 being 

a teletype 1yst.m, do•• not permit easy oheok1ng. Th• daily set-up 

publiahed in a k•y li•'t would haTe to oontain th• 1'olloring: · 

(1) Dally pin end lug ••t-up. 

(2) Dail7 t•tt1ng ot 128 plugs, 32 on each ot tour 4yl1nd•r•• 

(3) Daily 1etting ot t "A" pl~gl between the cyl11ulen and the ••lntor•• 

(4) Daily sett1ng 0£ 3 ~Bu plugs to chee.e the th,.. ••l•ctor p1n whe•l•• 

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The lug aet-up1 11111t be caretu lly •d• up in order to auure 1 to 6 1t•P• 

tor each cylinder per half•turn or th• drua. 1.e., per operation ot the 

maohine. The tiud teeth in the J10d•l in the db.gr•• a.r• probably not 

th• be1t arr&ngft8n.t po11ible but no matter what arrange111ent la used. lug 

pa~tern.s mu&t be carefully ,d•ri..,.d. 

b. :Mes•age Al1gnlll9n~s. - For eaoh ~•ssage th• pin wh••ls and oyliadera mu.at 

be aet. It the oylindera are 1et for ea.oh meas&g•, there is a chance 

tor ott ~ylinder 1ituationa- to ocour whioh may lead to recon1truotion ot 

the maohine variabl••• To aToid auch ocourl"itno••• the cylind•rs oould 

be 1•roized tor each 'l18ssage. But thia al10 leads to a bad •itUation 

because. it the cylinders are •et the aame ~t the be&inning of each 

• .,aage. the cylinders will et•p in aJa4 out of pha•e between ~easage1 1 

•in•• all 1ylinder1 •1i8P at approximately the aame rate. Thia ai"'1&t1on 

could beoome very ~angerou1. Theretore, e1th•r aolution ia unde1ira~le. 

PL 86-36/50 USC 3605 

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.Inolo1ure l to AFsA Serial dated • ~~------ ---------- t.J ' • - J 
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• RE~ rn:ASaa13 • 

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BRIEF SECURI!Y ESTIMATE OF 'l'ELICRYPTO (continued) 

- 2 -

Inolosui-• 1 to A.FSA Serial dated l' ~ 1

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. U-OP 3ECRE1 ___ , ) _, __ 

EO 3 . 3 ( h) ( 2 ) 

PL 86-36/50 USC 3605 

.AFSl-412n,/egb 

15 Jun• 1951 

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~--:~ ~~~~,ll..e13 • ' -t. ~(ii~~~~ BRIEF SECU'B.lTT I:sTI'..!ATB OF 1'ELICRYPTO (contin'll•d) 

EO 3 . 3 ( h) ( 2 ) 

PL 86-36/50 USC 3605 

.U'IU.•412B/egb 

15 June 1951 

e. 8Ull&!7• - !eleorypto requiree too llPCh aet-up ti• tor 1 t to be pr&ot1cal 

tor UH 'by the u.s. Armed Forces. .ASAJl 2-l i• lBH 'VUl .. rable to oryptanalytio 

a.ttaok so that '.feleorypto would not bs any imprO"NMnt oftr the comparable 

ayatea now in u••• 

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REF ID:A58813 

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AFSA-412B/egb 

1$ June 19'1 

3. 3 (h) (2) 

86-36/50 use 3605 COYDlrl'S OH CBYPfll llODEL CI 

1. Ceypte:x, Model CI is simil-,r to 1'elecr,pto but differs from it in the 

f~ct th~t the pin wheel 8S&embl7 in Teleceypto is the 5:'U ~s M-209 sind in 

Cr.ypte:x, Kodel CI is aimil=ir to t.h•- !!lodifi.ed !Utgelin. with er~tic stepping. --

The p1tper on Cryptax., Model CI is deted 5 lugust 19$0 ond therefore 11:17 be J! 

.rorerwmer ot Teleceypto. Pem=ips there were difficulties in its '"nuf!lcture 

with the more complic~ted err.tic motion. 

2. The aecuri t studies recentl c:>rried out b !\FSA.- l2B were all on '1' lee to. 

The ae1;-up tim for Crypt.ex, JI e !'Il s i:r y o oper-:- or error 

would be the S"lt:',e PB Teleceypto. This time ::alone would ~,::>:pe .. r to m~ke the 

\ a,ata iapr.=.ctic~ble. 

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Incloaure 2 t~ 'iSA Serial d~ted 

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