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Operating Instructions for CSP-845 (a.k.a. M-138A)

Kind readers,

Below is a replica of the instructions for operating the CSP-845 as written by the Army in 1945. I have selected this Army version of the instructions because it is the clearest photocopy of a strip cipher operating manual that I have collected. The manual has be input using optical character recognition followed by reformatting to network format (HTML.) The formatting does not attempt to preserve the paragraph indenting and font sizes.

Thank you for your patience as we work to find a good copy of the Naval instructions from late 1945.




DECLASSIFIED
Authority NND 963016
by M NARA Date 6/27/96



CONFIDENTIAL

SPECIAL INSTRUCTIONS
FOR USING THE
STRIP CIPHER DEVICE

(Short Title: FEDB-1)



This document contains information affecting the national defense of the United States within the meaning of the Espionage Act, 50 U.S.C., 31 and 32, as amended. Its transmission or the revelation of its contents in any manner to an unauthorized person is prohibited by law.



DEREGISTERED
13 MAR 53
ROY R. PLUMLEY, MAJ. ARMOR






CONFIDENTIAL

SPECIAL INSTRUCTIONS
FOR USING THE
STRIP CIPHER DEVICE

(Short Title: FEDB-1)



This document contains information affecting the national defense of the United States within the meaning of the Espionage Act, 50 U.S.C., 31 and 32, as amended. Its transmission or the revelation of its contents in any manner to an unauthorized person is prohibited by law.


This document consists of
11 numbered pages
Verify upon receipt

Prepared under the supervision of the
War Department
for authorized Federal Agencies




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CONFIDENTIAL



FEDB-1


5 February 1945

"Special Instructions for Using the Strip Cipher Device" (short title: FEDB-1) is a registered CONFIDENTIAL document and will be handled accordingly. It contains detailed instructions for the use of cryptographic systems based upon the strip cipher device by authorized Federal agencies.

A record of the custodians of this document is held by the distributing agency. Reports of possession, transfer, or destruction of this document will be made as directed by the distributing agency. Any reference to this document in unclassified correspondence should be by short title and register number only.

Loss or subjection to compromise of this document will be reported to the distributing agency by the fastest means available.




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CONFIDENTIAL

TABLE OF CONTENTS

Section Paragraphs Pages
I. Description 1- 6 3- 6
II. Operation 7- 9 7- 9
Appendix 10-11

SECTION I

DESCRIPTION

Paragraph
Component parts of the system 1
Keying elements 2
Indicators 3
Method of selecting message indicators 4
Length of messages 5
Paraphrasing 6

1. Component parts of the system. - The items necessary for the operation of a strip cipher system are a strip cipher device, an alphabet set, and a key list.

a. Strip cipher device. - The strip cipher device bearing the title CSP 845 consists of an aluminum or plastic base on which is formed a series of channels or grooves into which alphabet strips may be inserted and slid horizontally. A vertical rule called the reading guide, which can be slid to the right or left, is used for marking a specific column of letters to be copied. At each end of the channels is a stop bar. When the aluminum CSP 845 is used, the strips are inserted from the side. When the plastic CSP 845 is used, the strips should be inserted from the center; if the strips buckle, the cover plates at the edges of the device should be removed and the ball bearings and springs taken out. The strips should then slide freely.

b. Alphabet set. - Sets of alphabet strips, that is, strips of paper bearing random-mixed alphabets, are issued for use with the CSP 845. Each alphabet strip bears the following data:

(1) On one side:

(a) A random-mixed alphabet of 26 letters, repeated, making a sequence of 52 letters. The two alphabets are separated by a vertical black line.
(b) A strip number at the left end of the strip, identifying the particular strip in the alphabet set. The numbers run from 0l to 00 and are used in selecting the strips when preparing a device for use.
(c) The classification of the strip - whether SECRET, CONFIDENTIAL, or RESTRICTED - immediately to the left of the repeated alphabets.
(d) An identification symbol immediately to the right of the repeated alphabets, specifying the particular alphabet set to which the strip belongs. The symbol consists of the initials of the using agency and a number. All strips belonging to the same set bear the same identification symbol.




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(2) On the reverse side: The register number of the particular alphabet set to which the strip belongs. All strips belonging to the same set have the same register number. When an alphabet set is issued, the register number appears on the back of strip 01. It is recommended that this number be written by each holder on the back of all the other strips.

c. Key lists. - Each copy of a key list bears a register number for accounting purposes. The key list consists of the following two types of tables:

(1) Numerical keys
(2) Channel elimination numbers
(Sample tables appear in the Appendix.)


2. Keying elements. - In preparing the device for encipherment or decipherment, the operator uses two keying elements: a daily keying element and a message keying element.

a. Daily keying element. - The selection of strips to be used and the order in which the strips are placed in the device constitute the daily keying element and are controlled by the table of numerical keys (see sample Table I in Appendix). This table contains 31 numerical sequences. The date upon which a numerical key is to he used is indicated at the left of the sequence. Each key is effective for twenty-four hours on the date shown. The numbers in the key refer to the strip numbers; the order in which the numbers appear in the sequence indicates the order in which the strips are to be placed in the device.

b. Message keying element. - The "channel elimination" or "interruptor" scheme of encipherment is used with strip cipher systems. In order to maintain a high degree of security, both the particular channels eliminated and the total number of channels eliminated should vary among messages enciphered on the same day. The internal message indicator is the message keying element and determines the number and identity of channels eliminated in enciphering or deciphering a particular message.


3. Indicators. - Every message will bear two indicators, a system indicator and an external message indicator.

a. System indicator. - The system indicator is a five-letter group which identities the specific strip cipher system used in encipherment. System indicators to be used during a particular period are found in the effective key list. Some key lists may not contain indicators for each classification of messages. If an indicator is not provided for the classification of the message being enciphered, use the indicator provided (or, if two indicators are provided, use the indicator for the classification closest to that of the message) and bury the classification of the message in the plain text. The abbreviation TOPSEC will be buried within the plain text of TOP SECRET messages. The system indicator is transmitted as the first and last groups of the message.

b. Message indicators. - Every message will carry an external message indicator, from which the internal message indicator is derived.

(1) External message indicator. - The external message indicator is a five-letter group transmitted as the second and next-to-last groups of the message. It will be different for every message or message part.




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(2) Internal message indicator. - The internal message indicator is a key which contains from one to five numbers and which indicates the particular channels to be eliminated in enciphering or deciphering a message. The internal message indicator is never transmitted.

c. Position of indicators. - The following example illustrates the position of the system indicator and external message indicator in relation to the cipher text:

 PDLNB  LBKGN--------CIPHER TEXT-------LBKGN  PDLNB
 |      |                             |       |
 |      -- External Message Indicator--       |
 |                                            |
 ---------------System Indicator---------------

4. Method of selecting message indicators.

a. Select at random five different letters of the alphabet, for example, LBKGN. (Bona fide words should not be selected and may be used only if they occur by chance.) This group of five different letters becomes the external message indicator.

b. Refer to the current table of channel elimination numbers in the key list (see sample Table II in Appendix). This table contains 35 number sequences, most of which contain blanks. The numbers at the left and right of the first 31 sequences indicate the date. (The last four lines are required because five successive lines of the table are used in deriving each internal message indicator; on the thirty-first of the month, for instance, lines 31 to 35 will be used. *) Above and below the number sequences appears a normal alphabet, each letter of which designates a column in which numerical equivalents are to be found. The numbers in the sequences refer to the channels of the device, not to the numbers on the alphabet strips.

(1) In the line corresponding to the date of the message find the number appearing under the first letter of the external message indicator (i. e., the number which is in the column designated by the first letter of the external message indicator).
(2) In the line immediately below the current date line find the number appearing under the second letter of the external message indicator.
(3) In a similar manner, in the second line below the date line find the number appearing under the third letter of the external message indicator; in the third line below the date line find the number appearing under the fourth letter; and in the fourth line below the date line find the number appearing under the fifth letter.
(4) The numbers thus derived form the internal message indicator and designate the channels to be eliminated.

c. In some cases it will be found that for a particular letter of the external message indicator there is no corresponding number in the appropriate line of the channel elimination table or that the number is the same as a number derived from a pre-

------------

* In some key lists, Table II may contain 31 sequences, none of which contains blanks. With such tables use as many more lines as are required from lines 1 to 4 of the same table when the date of the messages is 28, 29, 30, or 31.




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vious letter of the indicator. In either case the number of channels eliminated will be less than five. Although any number of channels from one to five may possibly be eliminated by the external message indicator, the external message indicator itself will always remain a five-letter group.

d. Assume that LBKGN is chosen as the external message indicator, that the date of the message is 29 January, and that Table II in the Appendix is the table of channel elimination numbers currently in use.

(1) In line 29 (corresponding to the date of the message) a blank appears below L; therefore no channel will be eliminated by the first letter of the indicator.
(2) In line 30 the number 27 appears below B, the second letter of the indicator; therefore the twenty-seventh channel will be eliminated.
(3) In line 31, the number 27 appears below K, the third letter of the indicator. Since the twenty-seventh channel has already been eliminated, no channel will be eliminated by this letter of the indicator.
(4) In line 32, the number 22 appears below G, the fourth letter of the indicator, and the twenty-second channel will be eliminated.
(5) In line 33, the number 10 appears below N, the fifth letter of the indicator, and the tenth channel will be eliminated.
(6) Thus, the internal message indicator derived from the sample external message indicator LBKGN consists of three numbers, 27, 22, and 10, and the twenty-seventh, twenty-second, and tenth channels will be eliminated.


5. Length of messages. - If the cryptographed text of a message will exceed 100 five-letter groups, divide the plain text into two or more approximately equal lengths so that no part will exceed 100 five-letter groups. Select a new external message indicator for each part. The system indicator and external message indicator are transmitted at the beginning and end of each part.


6. Paraphrasing. - Paraphrasing is required when:

a. A message enciphered in a strip cipher system is re-enciphered in a strip cipher system. (A different external message indicator must be used.)

b. A message enciphered in a strip cipher system is re-enciphered in any other cryptographic system. *

c. A message enciphered in any other cryptographic system * is re-enciphered in a strip cipher system.

d. Information contained in a message enciphered in a strip cipher system is to be released to the public.

e. Information which has been released to the public is to be enciphered in a strip cipher system.


------------

* Paraphrasing is not required in certain cryptographic systems. Instruction documents for such systems state the exceptions to the necessity for paraphrasing.




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SECTION II

OPERATION




                                                               Paragraph
 Encipherment                                                              7
 Decipherment                                                              8
 Security precautions                                                      9

7. Encipherment. - At the beginning of each cryptographic period, insert the alphabet strips in the channels of the device, from the top downward, in accordance with the daily key given in the current table of numerical keys. To encipher a message, proceed as follows:

a. Select at random an external message indicator of five different letters. Determine the channels to be eliminated in accordance with the procedure outlined in paragraph 4. Withdraw the strips from the channels designated by the internal message indicator, counting the channels from the top downward. (The numbers of the internal message indicator refer to the channels of the device, not to the strip numbers.) Reverse the strips which have been withdrawn, so that the blank sides are exposed, and reinsert them part way in the same channels.

b. Move the reading guide to the extreme left position.

c. Align the first 25 to 29 letters of the plain-text in a vertical column, starting at the top, under each X of the Index Strip (which appears at the top of the device). If the letter sought appears to the right of the center vertical line on the alphabet strip, that is, in the right-hand alphabet, slide the strip to the right and align the letter under the right-hand. X of the Index Strip. If the letter appears to the left of the center vertical line, that is, in the left-hand alphabet, slide the strip to the left and align the letter under the left-hand X. This operation is most conveniently accomplished by placing the eraser of a lead pencil on the desired letter and pushing the alphabet strip into position.

d. When all of the 25 to 29 plain-text letters have been set up, check the plain-text column to make sure none of the strips have been moved accidentally.

e. With the plain-text letters in position under the X's of the Index Strip, there are 25 different cipher generatrices, or columns of letters, under the 25 generatrix numbers between the X's on the Index Strip. Move the reading guide until its right edge is adjacent to a generatrix number, selected at random, on the Index Strip. Make a note of the generatrix number so that it will not be used again in enciphering the message or message part.

CAUTION: NEVER SELECT EITHER OF THE PLAIN-TEXT COLUMNS AS A CIPHER GENERATRIX.

f. Record in five-letter groups the cipher text appearing at the right edge of the reading guide.

(1) Because the 25 to 29 letters to be recorded are distributed more or less irregularly over 30 channels, care must be exercised in copying the cipher letters.
(2) When the first plain-text setup contains 26 to 29 letters, the last cipher group recorded from the cipher generatrix will be incomplete. Make that group a complete five-letter group with the first letters of the cipher generatrix selected for the next plain-text setup.




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g. Slide the reading guide to the extreme left again, set up the next 25 to 29 letters of plain text under either X of the Index Strip, and repeat the process until the message has been completely enciphered.

h. If the last group of the message or message part is not a complete group of five letters, complete it by adding the necessary number of X's after the cipher text. Never encipher these additional X's.


8. Decipherment. - Insert the proper alphabet strips in the device in correct order, in accordance with the daily key; as determined by the system indicator in the message. To decipher the message, proceed as follows:

a. Derive the internal message indicator from the external message indicator according to the procedure explained in paragraph 4, and withdraw the strips from the channels designated by the internal message indicator. Reverse the strips and reinsert them part way in the channels.

b. Move the reading guide to the extreme left position.

c. Align the first 25 to 29 letters of cipher text in a vertical column under each X of the Index Strip. A cipher letter may be set up under either X, depending on the position of the cipher letter either to the right or left of the center vertical line on the alphabet strip.

d. Check the column of cipher text under either X to make sure none of the strips have been moved accidentally.

e. There are now 25 different generatrices between the cipher-text columns under the two X's. One of these will be plain text. The reading guide will be useful in finding the plain-text generatrix.

f. Record the plain text in proper word lengths.

g. Slide the reading guide to the extreme left again, and repeat the procedure with the rest of the cipher text until the message has been completely deciphered.

h. Delete any final X's in the last cipher-text group before attempting decipherment of that group.


9. Security precautions. - The following rules must be followed closely to protect the security of the system:

a. The original or repeated plain-text column will never be selected as a cipher generatrix.

b. The same generatrix number will never be selected twice in enciphering a message or message part.

e. Generatrix numbers will always be selected in an irregular manner. The selection of generatrix numbers must never be made according to a prearranged or regular pattern.

d. The five different letters of the external message indicator will be selected at random.

e. A message indicator which eliminates fewer than five channels will not be changed to one which will eliminate five channels.


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f. The plain text of a message will be divided into two or more approximately equal parts if the cryptographed text will exceed 100 five-letter groups.

g. Unenciphered X's will be used when it is necessary to complete the final cipher group of a message or message part.

h. Stereotyped words and phrases will be avoided, particularly at the beginning and end of messages. If messages constantly begin with such words as REFERENCE, REQUEST, CITE, etc., or end with ACKNOWLEDGE, ACKNOWLEDGMENT, ENDS, etc., the security of the system is weakened. Constant use of any word or phrase at the beginning or end of a message causes it to become a stereotype.




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APPENDIX
TABLE I.-NUMERICAL KEYS (SAMPLE TABLE)
JANUARY

Note: The sequence of numbers standing to the right of the column headed "Day of Month" gives the order in which the alphabet strips are to be inserted in the cipher device.

(For use with Alphabet Set XXX-616)

DAY OF
MONTH                                       NUMERICAL SEQUENCE
 1    43 44 82 37 73|32 74 85 20 70|71 40 18 19 63|08 34 93 28 46|38 92 29 56 47|49 66 39 33 62
 2    38 44 65 34 26|67 95 11 76 55|24 88 00 15 56|13 43 71 12 72|54 79 41 07 51|49 36 74 35 97
 3    09 99 55 91 86|82 05 64 89 43|78 42 24 20 18|77 65 26 45 71|22 23 85 30 17|03 49 87 37 00
 4    38 43 66 99 55|47 80 03 71 78|24 50 37 65 95|69 63 58 75 36|68 29 19 32 81|16 18 64 48 45
 5    36 44 87 09 32|45 97 60 00 75|66 06 04 55 22|80 31 48 89 52|03 24 96 79 57|43 37 85 02 71
 6    94 75 26 52 56|14 71 36 31 95|77 21 82 65 15|37 23 93 55 80|04 70 78 46 61|06 85 76 13 08
 7    08 69 48 55 85|13 41 77 76 03|05 43 67 39 83|20 75 45 19 47|21 27 98 29 58|61 38 82 54 22
 8    37 64 87 54 39|10 05 34 32 03|38 90 56 80 85|43 13 74 36 18|58 48 35 91 52|20 26 04 88 84
 9    06 40 82 37 67|51 24 91 23 92|15 32 77 35 87|09 41 93 66 38|22 52 13 49 27|76 29 99 08 47
10    24 95 89 84 19|06 43 85 41 79|70 30 01 03 55|75 64 38 57 45|23 72 58 11 97|20 31 00 12 22
11    18 79 89 88 11|64 52 53 41 97|56 69 66 20 45|42 30 65 99 71|15 08 91 72 37|77 26 70 95 02
12    83 65 23 25 24|52 60 33 68 46|95 21 17 81 05|84 93 35 50 66|58 98 13 32 61|02 97 20 04 94
13    10 40 79 28 48|32 63 35 61 87|73 11 92 43 34|94 23 38 53 83|57 76 99 08 42|21 18 15 36 51
14    42 54 10 09 49|55 99 95 90 70|58 07 73 71 17|05 34 44 03 47|20 62 15 60 18|01 25 24 52 56
15    43 31 27 04 85|88 82 05 53 52|41 94 47 60 95|42 39 22 80 77|30 89 09 75 74|93 06 72 14 91
16    29 42 83 68 96|47 93 91 58 59|78 88 37 56 69|07 17 13 08 40|03 15 12 36 09|85 05 81 92 06
17    08 79 64 92 67|73 84 86 55 58|52 21 13 62 66|38 27 98 89 46|85 25 09 37 06|43 15 97 57 54
18    72 24 78 20 93|63 11 21 92 60|59 83 54 37 53|80 07 22 03 13|40 01 56 15 04|51 30 52 98 64
19    72 78 16 38 20|81 92 59 80 35|57 58 11 68 26|77 34 03 67 84|25 49 73 69 44|15 28 66 96 22
20    27 21 53 16 60|47 95 88 40 68|54 90 04 93 31|52 05 34 57 23|66 25 48 11 92|24 35 82 67 75
21    56 98 57 22 76|69 80 96 29 94|00 23 60 61 28|55 50 31 83 15|67 27 41 09 86|79 59 01 89 84
22    42 49 14 03 04|88 36 13 29 68|62 59 71 74 81|75 87 54 55 86|43 25 58 12 02|90 09 56 70 85
23    12 10 03 45 34|81 09 66 01 20|50 54 71 84 48|98 18 60 31 19|33 00 91 13 88|23 79 97 75 35
24    22 52 73 49 10|32 85 42 08 01|75 37 34 48 62|63 71 95 13 43|69 45 26 35 82|04 76 46 55 66
25    02 63 56 21 07|77 84 76 03 82|42 23 46 38 91|99 55 64 12 97|29 00 74 32 96|28 60 37 22 26
26    24 16 94 07 03|47 97 42 56 87|41 05 80 91 82|74 21 64 72 85|37 63 59 76 14|70 28 90 18 38
27    33 84 94 18 79|54 44 72 97 75|38 19 70 45 56|80 65 12 23 66|32 87 95 35 29|51 04 88 71 77
28    80 85 63 11 64|43 08 89 96 17|40 31 76 73 66|09 48 44 67 28|93 79 82 58 88|87 84 41 32 77
29    26 03 04 76 38|70 85 50 84 29|75 09 30 73 40|68 49 98 18 82|96 28 60 13 56|91 44 93 20 74
30    23 70 86 13 95|18 90 21 69 63|67 87 92 20 56|46 14 27 35 64|55 28 06 12 00|52 09 50 65 36
31    49 61 10 72 75|73 74 12 87 70|18 99 29 94 40|37 47 67 15 91|64 38 57 34 89|90 11 68 02 28



                                SYSTEM INDICATOR: FDLNB



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APPENDIX
TABLE II.-CHANNEL ELIMINATION NUMBERS(SAMPLE TABLE)
JANUARY

(For use with Alphabet Set XXX-616)
System Indicator: PDLNB

DAY OF                                                                             DAY OF
MONTH A  B  C  D  E  F  G  H  I  J  K  L  M  N  O  P  Q  R  S  T  U  V  W  X  Y  Z MONTH
 1    4        1 30 29       10 14        6 18          27  9 24    17 23             1
 2    1    13    22     3 24 21     7    20    26 19  5 28       14       23          2
 3   26  3     2    17    25     5 16 19 27 10    23  1 22  7  9    18    21    15    3
 4   15    13    19    18 28     7 21 2 11        14    25       12    22    29       4
 5   19 27 20 10 21  8 23 22 29 24  5 25  2 12  4  6 26 17 11 15  7 28 30  9  3 13    5
 6   21     9 24  5 15    27    10    18    28 23 19 25 11     8 20        7 17  1    6
 7    3    10 23 11       22    27          19 25  1     8       21    20     6 14    7
 8   15 18 17 24  1 27    13     3 11 26       23 29     6    28    21    14 12 22    8
 9   28 16 26 27 29 15  4  5 14 23 25  6 22 10 12 20 30 18  1 21 17 11  7  3  9  2    9
 10      1    22       24          11 10 30 19  6        2  4 25     5    13     9   10
 11   6 14 29  8  9 17     4 18 23 21       20       22     2 24       28 26         11
 12     23 17 24     1 20 28  2    30    25 16       27  6  8  5  3 10       14 18   12
 13   1  3 27 26 16  9 12 30 19 25 29  8  5 15 21 14  6 23 10  4  7  2 22 28 13 17   13
 14     30     9    23 17  2 15       25        6    14 22  5  9    16    24 20  8   14
 15  22     4    28     8       11 17       20       26  7 23 27 14  5 19 16     9   15
 16   7 22 16 11 10 17 23 12 30 15 18  9  3 19 20  2 14  4 13 29 25 24 27  5 21  1   16
 17  15 30 19  4     9 25 29 20  5    12 24  2          16 22 26    21  6       10   17
 18  18           9 10  7 15     3    28 25    17 29 23 24 16 20       11    12      18
 19  12 24 22    27    19 11 17 16 13  8     3 28 18     5 14    26        9    21   19
 20  28  3 15  6 30 26 24  1 18  2 11  5  7 10 21 27  4 14 20 29 17 16 19  8 25 12   20
 21  13 23 10       14    30       20 11 25 15                      22 27 28  2  8   21
 22   8             16    11 28     9 21        5 20     4  2    12    26  3         22
 23  12       13          17 10    18 14    21 19 23 11        9     4    29     3   23
 24  18 22 29    13 30 23 27          17  4     2  5 19       12     8    26  7      24
 25  13  4 26  1 22 17 19 10 11 21 23  8 24  2 27  9  6 15 16 29  5 30 28  3 20  7   25
 26  22    20 21     4    12     5 28    17    15        3  1     8     2     9  6   26
 27  27  7  9  6 21  5 25  8 17 27 18 30 12 22 11  1 16 23 19  4  3 13 20 10 15 29   27
 28  26 18 24 11 10 30 27 29        6 13     5  3       21  1    14    26       20   26
 29         6  8  9       26       10    27 14 11 19  4 16 13 23 29       18 28  5   29
 30  10 27       15 26 23    30  1  6 20 17 21     8 13 19    11  4 29     2 22      30
 31  15  5 10 29 13 19     2 17 28 27  4  8 25 20 14  7  9 16 18  3 23 12 11 21 26   31
 32        17          22  8  2    29    30       23 13 19 12              6     7   32
 33         4  7          27 22    12     3 10    16 30 26     1     2 28 17 19 20   33
 34     11 15 19 26       18       25       23             21  7 22 13     8     3   34
 35  26  4  1 29 21  2 28  3 18 22  9 15 11 12  6 16  8 27 30 13 24 20 23 10  7 19   35

  A  E  C  D  E  F  C  H  I  J  K  L  M  N  0  F  Q  R  E  T  U  V  W  X  Y  Z 

DECLASSIFIED
Authority NND 963016
by M NARA Date 6/27/96

11





REFERENCES:

The information enclosed here relating to the strip cipher was OCR scanned and reformatted for the Internet from:
War Department (1945) Special Instructions For Using The Strip Cipher Device (short title: FEDB-1) This is available from NARA; NSA Historical Collections 190/37/7/1, NR 2288 CBLL35 12804A 19450205 , 1945 (Box 798, F: 2288, pp 12)

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