-,. t i ,-

REF ID:A66357 

St.~:t- ~ 

R 0 T <- '\/ G.A!J.. 

JulJ 11, ltll. 

hu- ~tr TraAdeU: 

I • •••lt•inc 1se ... nt11 a •n•4 11uopal.1 et the three 

leotu ... I PT• 1ut wet. Toa will ti.ad tat I baTa aadM9'tl'td tt •et wi.tla 

71ar re--9.-10• tbat it 'be ••• u brief ae p111111i.. , .. ...,. I ba•• 1••• 

tt tu 1tar enr,.. •ad ••• at»br••lat•d tbe ••tliae "" neta. If ••· Jleu• 

1d"'81 •, aad l wf.11 be 1l&d tt eatead tbl1 , ... 

., r·--· .... _ ...1111 acat• ter tbe •• .., pleuaat Ti•it 

J'ft IMltled .. to ban, bd fn' tla1 -1 ltftNie1 whleh JOU &acl JeV Hl1•••1 

---• .._. •• -dvtmltlle whole wet. 

-~ir Karl TrueauU, -... d .. a1'tll'l 1 ll.O.T .O., 

·Gimp Altro• fa1 l, ... ...,.ri, •. ~. 

liaoerelf J•ur•, 

@\pproved for Release by NSA on - -11 22 2013 pursuant to E.O. 1352§ 
J.1 

I .. 

I 

: 

I : 

• Synop11I of a oour11 or t~~o~~Jf~Ef~"7 and Ciphtl"I, given betofe tb1 

1tudtnt1 of the R.O.T.C., Caap-m& •• r.d .~.!, L.tt.= 511.,.r, R. J., July 6-S. 11211 

bJ 

w. 1, friedman, Code Compilation 8eot1on, Oftlce of the Ohl1f 81gnal Oftlo1r, 

Signal Corp1, U,8.Aray. 

·-·-----------·--------------- lint Leoture, Jul1 6. 

l. Introduotor1 r111&rka. Brief hiatorioal tUl"Tt$ of 1ubJ1ct. Great adYano11 ... 4, in 

reoent 71are both in method• &ad in analy1l1. 

2. Detinitiona, 01'Jptography. Cipher. Knoipherlag;Dloiphering. Plain text; Olpher Text, 

Ood•. lncodlng; Deoodina:. Plain text; Code text. 1Doiph1r1d Code • . 3. Coapari1on of ad'fantag11 and cli1&clftlltage1 of ood.11 and oiph1r1. Sharp 411tlnctioa ~.t ... en code and cipher in .. dern Ol'JPtograp ..... 

4, Lia1tatione or both ood• and cipher. Th• 'U•• e1-ent S.n 1olu.tion mnt 1aportant ~n 

JliU.tary ciphera or cod••, beoaue no practical eyata yet. d1ri11d ia lneoluble. 

5, Influence of rtoent rapid ·advance in radio on the uee ot oeyptograpbic meane or c••· 

munication in wartar•. 

6. Neoe11it7 for proper training of ottio•r• and 1peoiali1t1 in the uee of oodt and oipher 

Beriouan••• of reeult1 of failure to obaerYe fundmmental rulee and preoaution1. 

An appreciation of thi• feature 11 to be f o~nd ia a etudy of the prinoip1'1 Uled 

in the 1olution, or aaaly1i1 of cipher1. 

7, .AllalJ•il of Ciphere. Principle• of llechanbm of a written, alphabetical language .• 

Frtquenoy table1. Proport1ona of Yowell and con1onant1. Relati•• order of trequenor 

or varioue letter•, and oombinationetf lettel'I. Th• two principal olaa•e• of 

oiphera: Traa1po1iti1n Clpher1; 8ubetitut1on Ciphera. Kxaapl .. of eaoh. Method 

of diatingui1hing. Varioue type• of tran1poaition oiphtr1. Method of Solution. 

a. 8ub1titition Clph1r1. The kinda of alpbab•t•. Clph1r alphabet•, normal alphab1t1, 

direot • reTened, aiud, reciprooal. Slap le or single alphabet eubat:l.tution 

cipher•. llultlple alphabet eu'b8titut1on cipnera. Tb• u.s.Army Diek. Pla1tair. 

81oond Leoture, July 7. · ,1. Review of general principl.u of traaepod. ti on aad eubati tutioa c:Lphen. 

'· 2 .• Daaonetration of the 1011.\tioa of a typical four-alphabet 1ubatitution a:Lpher. 

Repetitiona or reourreno... Principle of faotoring the interY&l between the•• 

recurreno•• in cipher text. Oluea to number of alphabet• inyolyed. AnalJ•i• of 

frequency table• prepared upon 'ba118 of the nuaber of alpbabete • 

.. ll!llit .,_, reaeone for '\he 11apioit7 of th• 101\ltion. Short k•J vs. a. long or a Otll• 

tiou~'aa tey. Known alpbabet1 (direct or l'Yera1d norml) ••. mixed or unknown 

alp~iabMie. 

•• 

5. 

6. 

I 

CoJTeotion of errore. lrror1 in enciphering. lrrora in telegraphic traaamlaa:Lon • 

Brfore in cleoiphering. Krror1 in copying • 

lumJ)lea or deipb1r1d Gerau •••aaH taken fro• one dq'• aotl•ity. The 1tudy of 

time factor in thHe ao lvtiou .• 

'l'h• reflu~r•nta of a oipher tor ailtarr field ue. form• euitable tor t11egraph7. , ilut: not be longer than original text. •mJ can be in po1111a:lon ot all dete.11.e 

'· of th• •r•t•. Onl7 thing kept eearet 11 the k•J applJina: to particular meuag11. 

·: 

It ,4.n1,tnaent u1ed, auat acbd.t poHeeeion by •••1· llethod or 1nciphenaent ud 

deqiph•rmnt mu1t ba d.aple, deand no etrain. Complex proe•••H iapo1aibl1 on r~el.d. 87at .. ll\1llt admit of •P••4J oorraction of error1. Oonforaing to all pre• 

oediJng, a71te aut be auoh that aolution of 50 to 200 meeaagH all in ••• ke7 

ia a difficult matter--euf f1ciant to delar eolutlon tor auoh length of time that 

inf onaation 11 Y&luel••• when eo1Y1d. 

7, lxpilaaatioa. ot the nn U.8.AnQI Multiple Diak Cipher DeYloe. Der'fing a numerloal - ke7 from a tey wrd or a k&J phrase. 
REF•2In: A6635 7 

Third 14ot¥e, .July 8. 

1. Code. ReTi.,, definitiou and d1•tinotion between code and cipher. 

2. The vanou. tnH of cod••. Cemerclal. Gov.enemental. looDOllf. 8eoreo1. 

Alphabetical or one.,an otdea. l\andomiaed, or tw..,.rt oodea. Mn.nta1q 

and diaad'f&ntagee of eaoh. Neoe1ait1 of furth•r•eaoiphel'llent tor ••oret 

alplabetloal cod... N•oeeaity of careful attention to randoaiaed 00411. 

Secwity in latt•r oonaie'\a in r•arrang•ent of code equi.Talent• tra 

till• to ts.... Meaning of "MY edition, or obange in code". 

3. The Anny Field OodH. General d.e11aription of content• and type ot groupe. Phru•, 

wrdll, number•, ayll&blet, letten, tiae groupt, null.II, blal!Jta. 

4. The UmitaUone of the Ueld cod••· Reduced •i••• and oon1-au1nt •••11 na..'bulaJ"1. 

Heceaaity of becoming familiar with content•. lleke code ••••ac• fit tbe 

code book, not •lee veraa. 

5. Safegurding the ood1. R.euone for preoautiou to be found iJ:a pa1t eap.-iao .. &ad 

1tudy of the anal.rel• of oode. 

6. General rule•. N10111i·ty for preaerTing complete a1or1oy of the book S:tltlt .. aiaet 

unauthoriaed eight, photogJ"apha, e\o. Coaproai•• of a tingle copy nto•••i• 

tate• complete wlthdra•l of all cople1 and iaaue of new edition. V•r-t 

expeuiTe, till• loat • danger, eta. 

All code aeaeag11 ot equal iaportanc1 to the ••"'1 code 111•1ng ••cti1n. 

Solution• 1n non-imporiut meHagu great aid in aolutS.on of i•portut. 

Hence, in aotual arlare, reetrlot traffic to loaat poa1ible U.alt. The 

amount of material int•rcepted ia usually the deciding :t•otor in eo ltJtion. 

7. 8p1cifia rul11. ~••lfiiia once tran1mitt14 in one fora pf alpher or code auat n•••r be 

r1peat.•d in any other f ol"m whateoenr. Demonetn.tion of cue ta aotual 

10 lution of new Qeran ood• from three ••••1•• lnt1roept1d. If abao 1v.tel1 

neaH•IU"J to repMt in another tona, ••••age m11t be paraphruecl. l&plan. 

ation-cbanging about the n ru. phPu•e, 11nteao11. llue nn mt11ag1 

b .. r i...t ree .. blano• to original. a. Mea.age onoe ••nt in code or o:Lpher 

aut neT•r be ••nt in clear; lad doe vu1a. a. lteftr iuen plain tot •f 

•DJ kind in oode or oipher ........ nor pv.notutien,o~breTiatiou, eto. 111 

clear. •· Plain teat and equi:nlent oode tea.'\ aut nenr applU" ea ••• 

ab1et of paper for tile. Work 1h11t1 auat be ... tro7e4 b7 burning. Plain 

text ehe•t• muat never be filed attaohtd to cipher or code 1h1eta. 

a. Brief de1'cription of pr:lnoip14a of anal.J•i• of 0041. R1con1tr110-.1on of the 0041 

boot. Breuing up th• unknown '\ext into a aerl•• of ••t• of group1. ~tuey of the beb&Tiour of the .,. .. :Lov.1 typea of elea1nt1 going to make up 

intelligible text. 'lordl• varioua natur11. Pr1po1itiou, aoune, adJeotiTea, 

Terba, eta. all behave dlfter1ni11. 

9. 8oluti1on b)' ooaparle.._r aaaloa. Danger of at1r1otn14 •••••&•• or report. of u7 

kinda. luat be avoided baoau11 eaei11t •ol•ed. Solution by firat prinotplta. 

10.The 'rtp•r u1e of the oode to aake eoluion by Urat prlnoiplea aore difficult. Dange1' 

et addr11111 and eignaturea. 011 of 8p11Ung group• to be Urd.ttcl eo tar 

u .PO•tiblt. The7 are ..Utet p•.rt of the code. U•• ot the ftrianta and oullt 

or non•aign1fioant groupe. 

11./ 0.n.ral 8UDlat"J' •