Thomas Jefferson Papers
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# I. Description of Method

[18 Apr. 1802]

Method of using Mr. Patterson’s cypher.

1st. Operation.—In writing the original1 paper which is to be cyphered, use no capitals, write the letters disjoined, equidistant, and those of each line vertically under those of the one next above. this will be greatly facilitated, by using common black-lines, chequered by black-lines drawn vertically, so that you may place a letter between every two vertical black-lines. the letters on your paper will thus be formed into vertical rows as distinct as the horizontal lines.2

2d. Operation.—To cypher. divide the vertical rows of the page into vertical columns of 9 letters or rows in breadth each, as far as the letters or rows of the line will hold out. the last will probably be a fractional part of a column. number the vertical rows of each column from 1 to 9. in regular order. then on the paper to be sent to your correspondent, begin as many horizontal lines as there are vertical rows in your original, by writing in the beginning3 of each of every 9 horizontal lines as many insignificant letters from one to nine as you please; not in regular order from one to nine, but interverting the order of the numbers arbitrarily. suppose4 e.g. you write 8. insignificant letters in the first line, 3.5 in the 2cd. 1. in the 3rd. 6 in the 4th. &c. you will thus have the horizontal lines of your 2cd. paper formed into horizontal bands of 9 lines each, of which this, for instance, will be the key, or key of insignificant letters as it may be called.

8.3.1.6.9.4.7.2.5. | 2.9.1.8.4.6.3.7.5. | 3.6.9.2.8.5.7.4.1 6 then copy the vertical lines of the 1st. paper, or original, horizontally, line for line, on the 2cd.; the columns in regular succession, but the vertical lines of each arbitrarily; as suppose you copy first the 1st. vertical line of the 1st. column, the 5th. next, then the 2cd. then the 8th. &c. according to this, which may be called the key of lines

1.5.2.8.7.9.6.3.4. | 8.3.6.1.4.7.2.5.9. | 7.3.5.8.4.1.9.2.6. | 3.2.1.

then fill up the ends of the lines with insignificant letters, so as to make them appear of even lengths, and the whole7 is done.8 your correspondent is to be furnished with the keys thus.9

 key of letters. 8.3.1.6.9.4.7.2.5. | 2.9.1.8.4.6.3.7.5. | 3.6.9.2.8.5.7.4.1. | 2.1.3. key of lines. 1.5.2.8.7.9.6.3.4. | 8.3.6.1.4.7.2.5.9. | 7.3.5.8.4.1.9.2.6. | 3.2.1.

3d. Operation.—To decypher. your correspondent takes the10 cyphered paper you have sent him, and first, by the key of letters, he dashes his pen through all the insignificant letters, at the beginning11 of every line. then he prefixes to the lines the numbers taken from the key of lines in the order in which they are arranged in the key. then he copies the 1st. line of the 1st. horizontal band, writing, on a seperate paper, the letters vertically one under another (but no exactness is necessary as in the original operation.) he proceeds next to copy line No. 2. vertically also, placing it’s letters by the side of those of his first vertical line: then No. 3. and so on to No. 9. of the first horizontal band. then he copies line No. 1. of the 2cd. horizontal band, No. 2. No. 3. &c. in the regular order of the lines and bands. when he comes to the insignificant letters at the ends of the lines, they will betray themselves at once by their incoherence, and he proceeds no further. this third paper will then, in it’s letters and lines, be the true counterpart of the 1st. or original.12

(); in Meriwether Lewis’s hand; undated; at head of text: “Cypher. Mr. Patterson’s”; with emendations in TJ’s hand (see notes below); endorsed by Livingston. (: TJ Papers, 128:22130); entirely in TJ’s hand; undated; at head of text: “Method of using mr Patterson’s cypher”; endorsed: “Cypher mr Patterson’s.” (same, 232:41574); lacks endorsement. (); entirely in TJ’s hand; undated; on recto of of Document II; at head of text: “Method of using this cypher”; endorsed: “Robert Patterson’s cypher”; with significant variations as noted below. Enclosed in TJ to Robert R. Livingston, 18 Apr. 1802.

1Word interlined in in .

2Here in in , TJ partially erased “divide.” : “1st. operation. write your letter in horizontal lines, not distinguishing words, but each letter disjoined, & those of <one> each line falling vertically <over> under those of the preceding line. when done, divide the whole page into columns of not exceeding 9. letters each (counted horizontally) and number the vertical rows in each column with the figures 1. 2. 3. 4. &c.”

3Word corrected by TJ from “begining.”

4Word interlined by TJ.

5Digit apparently changed by TJ from “2” to “3,” here and in in .

6 in continues: “2.1.3.”

7 in : “work.”

8: “2d. operation. transcribe the vertical lines, horizontally, not in the order of the numbers 1. 2. 3. &c. but promiscuously, and making the <horizon> lines as horizontally transcribed, overjet one another by arbitrary & different numbers of letters. then fill the deficiencies of each line at both ends, with insignificant letters which however had better be of consonants & vowels duly mixed that they may not betray themselves.”

9: “3d. operation. state the key, by arranging the numbers of each line in the order in which they have been promiscuously written, and by the side of each number place the figure <shewi> expressing how many insignificant letters there are at the beginning of the line. this key may be <safely> sent in the letter as it would not probably be understood but would be better previously lodged with your correspondent, and changed from time to time by safe conveyances.”

10Word interlined by TJ.

11Word corrected by TJ from “begining.”

12: “4th. operation to decypher. first prefix to each line it’s proper number from the key, and dash out or erase the insignificant letters at each end of every line. then copy <the 1st. letter of the line No. 1. 2. 3. 4. &c. in their numerical order> the horizontal line No. 1. vertically, then No. 2. by it’s side, vertically also, No. 3. the same & so on; and when all the horizontal lines of the cyphered letter shall be written vertically in their due order, and one column after another, the <letter> paper may be read horizontally. to prevent mistakes in this last operation it will be well to mark every letter of the cyphered paper with a dot as you copy it, lest you should by mistake copy the same letter twice or not at all.”