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REF ID:A67561 It 

March 9, 1936 

MEMORAm:rru ON CIPH&:R DEVICE TYPE 11-138 

This morning I disclosed to Lieut. \Yenger, Code and Signal 

Section, l._vy Department, my idea for a modification of the Strip 

Cipher Device as follows: 

Arrange the device to consist of serially nwubered sections 

of five channels each. To set up the numerical key for the day 

arrange the sections lll serial order from l to 5 and insert the individual alphabets in the successive channels in accordance with the 

daily numerical key. Each message would begin with an indicator which 

would indicate arbitrariiy the order in which the sections were to be 

assembled. This would afford 120 different sectional arrangements. 

Vie commented upon this scheme with Mr. Rovrlett being present. 

During the course or the discussion the question came up as to weakness 

introduced by the fact that the sections were always of the same number 

of alphabets, in this case, five. During the course of the d1scuss1on 

I brought up the matter of the Treasury Department Device with its 30 

alphabets and noted that one of the obJections to it was that while we 

had found it extremely difficult to match lines containing 25 letters 

by means of statistics based upon coincidences, it might be that with 

30 letters, which gives 20~ more text, the matching of lines to determine 

which were in the same generatrix might be much easier. I then went on 

to say that with an arrangement such as I propose that if the sections 

were interchangeable this obJect1on to a 30-alphabet device would be 

eliminated and from that point on I suggested that one might have six 

sections of which only five would be selected according to the indicator. 

Continuing I said that I had given some thought to a device in which one 

could easily vary the number of alphabets in each section, but that I 

had not arrived at a practicable solution mechanically. 

Lieut. Wenger then suggested that w~ might make the sections 

themselves of unequal V11dths. Then I said, for example, supposing that 

Section l had 3 alphabets, Section 2, 8 alphabets, Section 3, 4 alphabets, 

Section 4, 1 alphabet and Section 5, 9 alphabets, totaling 25 alphabets, 

the message indicator would indicate the arrangement of these sections 

for each message so that each message would have 25 alphabets but arranged 

in different sections. I then said something about the packing of the 

sections in transporting the device and being able to pack them in a 

pyramidal arrangement on account of the different widths of the sections. 

Mr. Rowlett pointed out that if one had six sections varying in widths 

from 4 to 9 alphabets, thJB would afford a total of 39 alphabets available 

or which an individual message would use 30 to 35 alphabets depending upon 

lA\pproved for Release by NSA on 09-09-2013 pursuant to E. 0. 1352§ 
REF ID:A67561 

the indicator. At the same time this would combine the advantages or 

the 30 alphabet arrangement which affords 720 different arrangements or 

six sections. 

Lieut. Wenger said that he would give the proposal some thought 

and would talk it over with his associates. He stated that it seemed 

to him to have good poss1bil1t1es. 

~~~ ... ~~a:,,., .... , ...... 

William F. Friedman. 

I was present at the aboTe-mentioned conversation and, to '1113 

knowledge, the statements made in this memorandum are correct. 

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