Tool to decrypt / encode like B. Arnold, using a book cipher (recovered messages from the 17th century).
Arnold Cipher - dCode
Tag(s) : Homophonic Substitution Cipher
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Arnold Cipher
Arnold Cipher
The encryption used by John André and Benedict Arnold is called a Book Cipher. This type of encryption uses the disposition of words in a book (chapter, page, line). Thus, to achieve exactly the encryption/decryption of Arnold it is necessary to have the same version of the book he used: Commentaries on the Laws of England by William Blackstone or the Nathan Bailey dictionary. dCode does not have such numerized books.
Answers to Questions (FAQ)
What is Arnold cipher? (Definition)
Arnold's cipher is a book cipher using either William Blackstone's Commentaries on the Laws of England or Nathan Bailey's Dictionary.
How to encrypt using Arnold cipher?
Encryption requires a book (physical or scanned) with numbered pages.
In order to encrypt a word, it must be located among the pages of the book (which implies that the book is large enough and / or contains a maximum of words).
Each word is encoded by a triplet of numbers: a page number, a line number on that page and a word number on that line.
Example: 3,2,1 for the 1st word of the 2nd line of the 3rd page.
For little words, determinants, connecting words, etc. (from, to, a, the) the transmitter did not bother to encrypt them. Likewise, some proper names not being found in the book, they were often replaced by an initial, in the hope that the recipient would deduce them.
How to decrypt Arnold cipher?
Decryption requires knowing / possessing the book used during encryption. It is essential that it is the same book (or the same edition, with the same layout).
For each triplet (X, Y, Z), the receiver must open the book on page X, count line Y on the page, and note the word number Z on the line.
What are known Arnold coded messages?
Several messages dating from 1780 have been found:
| Original | Decrypted |
|---|---|
| I 293.9.7 to C-t B. 103.8.2 the 7th 152.9.17 that a F--- 112.9.17 and 22.8.29 were 105.9.50 to 4.9.71 in 62.8.20 with 163.8.19 A 22.8.19 at with 230.8.13 263.8.17 I gave Mr. S---y a 164.8.16 147.8.261 to be 209.9.216 in C----a and have from 163.8.17 to 163.8.17 58.8.27 to him. such 147.8.21 as I 164.9.5 147.9.16, which he 24.9.125 me has 169.9.23'd to you. I 129.8.7 46.9.22'd no 19.8.29 to 175.9.17 158.8.8 - or any 177.8.13 168.9.13. I 105.9.5 soon to 57.9.7 at 288.9.8 198.9.26 and most 230.8.12 by --- / 291.8.27 an 149.8.27 with 255.9.11 148.8.22, 182.4.28 in whom a 175.9.12 67.8.28 could be 196.9.16. The 177.8.8 is 103.8.19 to 22.9.3 and to 66.8.15. An 182.8.28, 169.8.25 be 260.8.5 205.9.3 near that 209.9.18 and 192.9.9'd to 224.9.9 on 188.8.13, or some 182.8.28 on 188.8.13 sent 185.6.24 to 95.9.124 an 104.8.1 | I wrote to C[ap]t[ain] B[eckwith] on the 7th [of] June, that a F[rench] fleet and army were expected to act in conjunction with the A[merican] army. At (with?) [the] same time / I gave Mr. S[tansbur]y a manifesto intended to be published in C[anad]a, and have from time to time communicated to him such intelligence as I thought / interesting, which he assures me he has transmitted to you. I have received no answer to my Letter, or any verbal Message - I expect soon to command West Point and most seriously (by?) wish an interview with [an] intelligent officer in whom a mutual confidence could be placed. The necessity is evident to arrange and to cooperate. An officer might be taken Prisoner near that Post and permitted to return on parole, or some officer on parole sent out to effect an exchange. |
| 120.9.7 W------- 105.9.5's on the 22.9.14 of 163.8.19 F----- 172.8.7s to 56.9.8 |30,000| 172.8.70 to 11.94.? in 62.8.20; if 179.8.25, 84.8.9'd, 177.9.28. N---- is 111.9.27.'d on 23.8.10 the 111.9.13 180.9.19 if his 180.8.21 are 179.8.25 255.8.17 for that 180.9.19, 44.8.9 --a-- is the 234.8.14 of 189.8.17 I 44.8.9 145.8.17 294.9.12 in 266.8.17 as well as 103.8.11 184.9.15 80.4.20. I 149.8.7 10.8.22'd the 57.9.71 at 288.9.9 198.9.26 as a 100.4.18 in 189.8.19 I can 221.8.6 the 173.8.19 102.8.26 236.8.21's and 289.8.17 will be in 175.9.7 87.8.7. The 166.8.11 of the 191.9.16 are 129.19.21 266.9.14 of the 286.8.20, and 291.8.27 to be on 163.9.4 115.8.16 114.8.25ing. 263.9.14 are 207.8.17ed 125.8.15 103.8.60 from this 294.8.50 104.9.26 -- If 84.8.9ed 294.9.12 129.8.7 only to 193.8.3 and the 64.9.5 290.9.20 245.8.3 be at an 99.8.14. The 204.8.2 253.8.7s are 159.8.10 the 187.8.11 of a 94.9.9ing 164.8.24, 279.8.16 but of a 238.8.25 93.9.28. | General W[ashington] expects on the arrival of the F[rench] troops to collect 30,000 troops to act in conjunction; if not disappointed, (?) N[ew York] is fixed on as the first object, if his numbers are not sufficient for that object, can --a--? is the second; of which I can inform you in time, as well as of every other design. I have accepted the command at West Point as a post in which I can render the most essential services and which will be in my disposal. The mass of the People are heartily tired of the War, and wish to be on their former footing. They are promised great events from this year's exertion. If disappointed you have only to persevere and the contest soon will be at an end. The present struggles are like the pangs of a dying man, violent but of a short duration. |
| As 158.9.25 and 115.9.12 are 226.9.3'd by 236.8.20ing 131.9.21 163.9.6, it is 177.8.6 that the 156.8.11'r 236.9.28 be 234.9.3ed as well as the 98.8.22s I 128.9.25 up, and a 159.8.5 for 236.8.21's 149.27 on and a 255.9.11 13.8.6'd for that 211.8.14 - which I have 168.8.20ed in a 158.8.8 189.6.17 10.9.9 this, 189.8.17 Sir 300.8.4 290.9.20 not, I 31.9.13 think 282.9.12. I am Sir, your Humble Servant. | As Life and fortune are risked by serving His Majesty, it is necessary that the latter shall be secured as well as the emoluments I give up, and a compensation for services agreed on and a sum / advanced for that purpose - which I have mentioned in a letter / which accompanies this, which Sir Henry will not, I believe, think / unreasonable. I am Sir, your humble Servant. |
| P.S. I have 125.8.15 61.8.28 in the 30.8.8er, but 30.8.8. S. 300.8.4 will 264.9.26 him with 231.9.27 223.8.1 in 116.8.19 he 14.8.9's the 61.8.28 196.9.16 in him, 189.8.17 294.9.29 39.4.24 48.8.19 228.8.23 183.8.2 me. The 30.8.8'er 290.9.20 39.9.24 me |200| 126.9.141s, and 190.8.11 the 220.8.50 to 45.8.10 A-----s, who is 222.9.15ed to 216.9.22 the 80.8.8 for Mr. 172.9.12 | P.S. I have great confidence in the Bearer, but beg S[ir] Henry will threaten him with his resentment in case he abuses the confidence placed in him, which will bring ruin on me. The Bearer will bring me 200 Guineas, and pay the remainder to Captain A-----s, who is requested to receive the deposit for Mr. Moore |
How to recognize a Arnold ciphertext?
Arnold's number is made of triplets of non-zero integers.
Small (unsignificant) words are not necessarily encoded.
What are the variants of the Arnold cipher?
Arnold's book cipher uses triplets (page, line, word). It can be simplified in (page, word) or even only (word) or complicated in (chapter, page, line, word).
It is also possible to extract not the word, but a single letter (page, line, word, letter).
The way to count the words or letters can also vary, without specific indication, impossible to know if an empty line counts or not, or if a compound word counts for 1 or 2 words.
When was Arnold cipher invented?
Arnold described this cipher in 1779 but it had certainly been used before.
Source code
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Arnold Cipher on dCode.fr [online website], retrieved on 2024-11-21,
