Unsolved Historical Ciphers

Several well-known unsolved ciphers such as the Voynich Manuscript, Beale ciphers, Dorabella cipher, etc. have been attracting attention of the worldwide cryptologic community (see, e.g., Elonka's List of Famous Unsolved Codes and Ciphers) but historical archives (and other publications) contain many other pieces written in codes and ciphers that remain unsolved. The following lists some of such pieces in the hope that only a fraction of the efforts directed to major cryptologic puzzles might contribute to the solution of these small puzzles.

(Recently broken ciphers are also listed.)

The reader is kindly asked to provide information if he/she knows or attains decipherment of any of these.

Postscript to King Ferdinand's Letter to his Ambassador in Rome (1498)

King Ferdinand's letter to Garcilaso de la Vega, his ambassador in Rome, of 31 August 1498 was deciphered by Parisi (2004) (pdf; p.115) but the last ten lines are in a different cipher and is left undecipehred.

Galende Diaz (1994), cited in another article, mentions a cipher of Garcilaso de la Vega preserved in the archives.

You can post your comments or solution here.

Spanish Letters (1497-1504)

BnF Espagnol 318 (Gallica) includes undeciphered letters. Ff.5-6 and f.116 employ known ciphers but the following three are in unknown ciphers:

f.122, no.95 A letter of 8 January 1497

f.120-121, no.94 Viceroy of Sicily to Ferdinand, 27 April 1503

f.118, no.93 (p.448 of pdf) Lorenzo Suarez to Ferdinand and Isabella, Venice, 24 February 1504

See another article.

You can post your comments or solution here.

A Spanish Letter (1504?)

PTR,LEG,54,DOC.13 is a letter entirely in cipher, not deciphered. It is filed with letters from 1504. The last line may be in a different cipher. There are many repetitive patterns (like "16e", "8ρ", "ogθ+", etc.) and it does not seem to be a very complicated system.

For contemporary Spanish ciphers, see another article.

You can post your comments or solution here.

Catherine of Aragon's letter to King Ferdinand (1509) Solved

I called for a solution of an undeciphered letter (1509) of Catherine of Aragon to her father, King Ferdinand at MTC3 in 2018. To my pleasant surprise, it was immediately solved by two people. See my blog post.

Spanish Cipher Letter to Emperor Charles V (1529) Solved

I solved in 2018 a cipher used in a letter (1529) to Emperor Charles V from Suarez de Figueroa, Spanish ambassador in Genoa. See another article.

Before that, I tackled a cipher in a letter (1543) from Suarez de Figueroa to Prince Philip. After some initial success, however, a plaintext was found in the archives. See another article.

Spanish Letters (1551)

Undeciphered letter of 1551 (PARES)

Undeciphered letter of 24 August 1551 (PARES)

For contemporary Spanish ciphers, see another article.

Letters from Duke of Guise? (ca. 1581)

I posted undeciphered letters to Mr de Mercoeur probably from the Duke of Guise in my new blog.

Vatican Ciphers Solved

Two ciphers of papal nucios (1625, 1628) were posted as challenge problems in 2018. I was the third to solve them. See another article.

Before that, I solved three Vatican ciphers from 1593. See another article in Cryptologia.

Solution of a similar ciphertext (1573) was described by Albert C. Leighton back in 1969. See another article

Bellaso's Ciphers Solved

Many of the ciphers presented in works of Giovan Battista Bellaso in the mid-16th century were solved by Tony Gaffney in 2009. The remaining four were solved by Norbert Biermann in 2016-2018. See the links at the end of another article (in Japanese).

French (or Italian) Ciphers (c.1590)

BnF fr.4715 in the French archives contains many undeciphered letters. I could solve some (at least partially) but three remains unsolved despite their seeming simplicity. See another article.

The French archives has many other cipher materials. In some cases, they can be solved with keys reconstructed from letters with decipherment. See the following articles:

Reading an Undeciphered Letter of the Duke of Mantua (1590, 1593)

Reading Undeciphered Letters to the Duke of Savoy (1593)

Reading an Undeciphered French Letter from Antwerp (1580)

Wallenstein (1626) Solved

A simpe substitution cipher used by Albrecht von Wallenstein during the Thirty Years' War was solved by Nagra in 2016. See another article.

Emperor Ferdinand III and Archduke Leopold (1640-1645) Solved

Emperor Ferdinand III and Archduke Leopold used cipher in their private correspondence in 1640-1645. In 2018, Thomas Ernst succeeded in codebreaking. The Habsburg brothers' cipher turned out to be essentially a numerical cipher with some figures guised in graphical symbols. See another article.

Two Ciphers of Imperial Ministers from the Thirty Years' War Period Solved

Two homophonic substitution ciphers of Imperial ministers from the time of the Thirty Years' War were solved in 2018. One was solved by Thomas Bosbach and Nagra independently. The other was solved by Thomas Bosbach. See another article.

Carl von Rabenhaupt (1646)

A letter (1646) of Carl von Rabenhaupt (Wikipedia), a Bohemian who fought for the Protestants during the Thirty Years' War, to Amalie Elisabeth, regent of Hesse-Kassel (Wikipedia), is presented in Klausis Krypto Kolumne (2016) and Crypto-World (7-8/2013; 9-10/2013; 11-12/2013). The cipher consists of two- or three-digit figures and other symbols.

This ciphertext has not been deciphered yet.

Ormonde-Maltravers Cipher (1634-1635)

Calendar of the manuscripts of the Marquess of Ormonde, K.P., preserved at Kilkenny (Internet Archive), p.28, includes two letters partially in code from Lord Maltraverse (Wikipedia), MP in the Parliament of Ireland, to Ormonde in 1634-1635.

Maltravers to Ormonde, 13 September 1634
My Lord of Kildare is long ago in England though I have not seen him, it is said he came over because he was 65 35 21 26 59 98 113 186 108 143 refused to see him because he brought no 28 69 49 50 70 44 89 from 186 99.

Maltravers to Ormonde, 22 January 1634-5 [i.e., 1635]
.... You desire to know what 93 185 95 hath written unto 99 149, concerning 98 10 44 79 47 8 59 for whom 270 thus hereafter of which I can give you no account of at all, only by what I hear it is like to go worser with him, rather than better, 95 186 98 hath written unto 98 218 97 much in praise of 100 174 103 in general, and particularly for his good carriage in 111 95 221 and upon his motion 93 31 174 99 is to be 64 99 11 79 85 35 12 69 28 29 79 44, in which courses 174 shall do well to continue.....

The underlined occurrences "44 79" and "79 44" seem to indicate these are combinations of frequent letters. Many cipher sequences are delimited with 91-111, which may be nulls.

Ormonde-Clanricarde Cipher (1644) Solved

A letter in cipher printed by Davys (1737) has been solved by the present author in 2011. The letter was one long known to historians. See another article.

Private Cipher between Charles I and Henrietta-Maria (1645)

While Charles I used various ciphers, a passage (8 April 1645) in the private cipher for use with the Queen appears to remain undeciphered. See another article.

Charles I in the Isle of Wight (1648)

Charles I's letters in cipher during his captivity in the Isle of Wight (1648) remain undeciphered. See another article.

Prince Rupert's Cipher with His Brother Maurice (1645)

An encoded letter Prince Rupert received from his brother soon after the Battle of Naseby is printed in Memoirs of Prince Rupert, and the cavaliers by Eliot Warburton (Google), p.133 and appears to be unsolved.

.... By your cipher, you may observe, that 15 26 342 148 136 13 325 162 84 212 26 334 61 340 199 39 328 353 149 49 329 26 351 397 150 100 148 212 66 336 156 217 28 229 355 82 16 15 194 229 214 84 324 131 293 252 355 150 293 148 231 22 194 228 293 323 151 351. Garrison, 6 15 148 64 229 354 37 323 217 41 398 373 150 172 170 48 227 214 293 148 66 84 270 361. Accordingly, 151 244 229 149 213 324 239 274 185 12 15.
Maurice to Rupert, Worcester, 7 July 1645

The highest number is 398. Considering that two-digit figures do not appear in succession, the code seems to be different from the ones Rupert used with Charles I or Nicholas at about the same time (see another article).

Prince Maurice to Lord Digby (1645) Solved

The British National Archives has an educational page that shows an image of a letter in cipher from Prince Maurice to Lord Digby dated 31 August 1645. Although it is not "unsolved" (see another article), it may be included here because the page encourages the reader to crack the code because "We don't know!" the content.

Charles II to Duke of Hamilton (1650)

Some passages in cipher in Charles II's letter to the Duke of Hamilton (1650) remain undeciphered. See another article.

Charles II's Letter by Pseudonym (1655) Solved

The cipher of Charles II's letter by a pseudonym J. Westrope was broken by Eric Sams and Julian Moore in 1977. The letter was one long known to historians. See another article.

Dutch ciphers (1653)

Thurloe State Papers include some undeciphered Dutch letters, for example: Beverning and Vande Perre to the Dutch ambassador Boreel at Paris, 1 September 1653 (NS) (British History Online).

Intercepted Letters (1656)

Thurloe State Papers include some undeciphered intercepted letters, for example:

An intercepted letter of du Gard in a letter to White, Brussels, 10 June 1656 NS (British History Online)

An intercepted letter, Brussels, 12 August 1656 NS (British History Online)

An intercepted letter, from Jo. Waddall, 22 August 1656 (British History Online)

French Cipher to Ambassador in Constantinople (1690) Partially Solved

Louis XIV's instructions in code to Castaignere, French ambassador in Constantinople, dated July-August 1690 are printed in Paul Rycaut, History of the Turks (Google), p.453 ff. This appears to be the letters John Davys deciphered around 1701 (see another article) but his deciphering is not known. The present author partially solved it (see another article).

French Cipher to Ambassador in Rome (1690)

Louis XIV's instructions in code to the Duke of Chaulnes, French ambassador in Rome, dated 10 July 1690, remain unsolved. See another article. While I was writing the relevant section therein, discussion started in Klausis Krypto Kolumne.

French Cipher Unsolved by John Wallis (1690)

Harry Thompson, The Man in the Iron Mask prints in the appendix a letter in a French cipher that John Wallis could not solve (see another article). It is one of the letters from Louvois to Lauzun in Ireland (27 May 1690), written about a month before the Battle of the Boyne.

French Cipher Despatch received by General Catinat (1691)

A coded letter of 1691 addressed to General Catinat appears to remain unsolved (see another article).

French Cipher Despatch of General Catinat (1702)

A coded letter of 15 September 1702 written by Marshal Catinat remains unsolved (see another article).

French Code during the American Revolutionary War (1779)

An encoded letter from Admiral D'Estaing to Gerard, French minister in Philadelphia, dated 30 April 1779 is preserved in William L. Clements Library, Clinton Papers, "vol 64:14". It begins as follows:

240 318 401 367 211 382 108 152 34 450 109 471 541 525 113 511 262 321 382 402 56 393 482 110 152 34 445 152 109 382 110 42 39 487 382 283 184 37 208 401 240 113 235 20 213 401 334 137 374 262 410 380 334 271 402 109 17 239 378 443 237 55 300 401 ....

The present author identified four French diplomatic codes in the same period (see another article) but none of them seems to decode this. The highest number used in this letter is 597, suggesting a smaller code than the diplomatic codes.

Cipher between James Madison and Philip Mazzei (1780) Solved

There is a portion in cipher in a letter James Madison received from an Italian, Philip Mazzei. See another article.

In 2015, when this page was mentioned in a German cryptology blog, Armin Krauss immediately responded with his solution. See another article.

Patterson's Cipher for Jefferson (1802) Solved

Patterson devised a new cipher system and sent Thomas Jefferson a challenge, which was deciphered in 2009 by Lawren M. Smithline. See another article.

Encoded Letter to Marshal Marmont (1807)

An Encoded letter to Marshal Marmont in 1807 is reproduced in J. Vilcoq, "Le Chiffre sous le Premier Empire", Revue Historique de L'Armée No.4 (1969). It begins with "Vous avez du recevoir Monsieur le General Marmont mes lettres des 8.14 et 20 courant" and the rest is wholly in code. The code consists of two-digit figures as well as alphabetical letters and other symbols.

Considering that Marmont used a relatively simple code of 150 entries in 1811 (see another article), this would not be a very complex system.

Encoded Letter from Berthier to Napoleon (1812)

An Encoded letter from Berthier to Napoleon dated 22 December 1812 is reproduced in J. Vilcoq, "Le Chiffre sous le Premier Empire", Revue Historique de L'Armée No.4 (1969). It begins with the following. See another article for Napoleonic ciphers that may be similar to this code. Considering that it bears a note: "Duplicata, Chiffre du Prince de Neufchâtel, La Primata a été déchiffrée", its decipherment may be found in some archives.

918 1045 1100 493 359 989 1105 73 710 432 118 718 544 810 1060 1135 1122 173 666 862 718 772 493 359 701 13 572 544 432 413 960 112 43 989 821 791 1030 811 999 1153 820 918 1045 1100 415 1048 623 236 559 854 946 851 168 854 1148 236 602 13 782 844 1238 656 69 823 803 741 536 280 669 1051 215 314 498 434 402 1193 238 1178 10 711 1100 1109 504 463 73 793 388 703 43 13 821 791 2 1135 1122 1087 566 476 982 853 354 289 13 741 536 1063 710 1388 889 410 443 994 ....
Berthier to Napoleon, 22 December 1812

Postscript in Code from Armstrong to Madison (1808)

A letter of 30 August 1808 from John Armstrong, US minister in France, to James Madison, secretary of state, has an undecoded postscript. The known plaintext of other letters may give a clue to its solution. See another article.

Ciphers Left Unsolved by Edgar Allan Poe (1841) Solved

In 1841, Edgar Allan Poe wrote a series of articles in a magazine, in which he solved simple ciphers sent by the reader. At the end of the series, Poe published two cryptograms sent by W. B. Tyler, which he did not solve. The first was solved independently by Terence Whalen (dissertation in 1991; published in 1994) and John Hodgson (1993), while the second was solved by Gil Broza in 2000. See another article.

The "Decoding the Civil War" Project

In 2016, the project "Decoding the Civil War" started to transcribe and decipher about 16,000 telegrams from The Thomas T. Eckert Papers. These papers belonged to Thomas T. Eckert, the head of the Union military telegraph office, and, though long thought to have been lost, were recently acquired by The Huntington Library. They include Union correspondence that has never been published. See another article for an overview of Civil War codes and ciphers.

Union Ciphers during the Civil War (1862)

Indiana Memory Digital Collections has cipher telegrams to Brigadier General Robert H. Milroy. One is from J.D. Cox, dated 3 December 1862 (here), and another is from G.M. Bascom, dated 4 December 1861 (here).

Probably, these employ a simple route transposition system. The context would be found in OR vol.24, around p.830 (see another article).

A Dictionary Code between Confederate Generals: J.E. Johnston and Robert E. Lee (1862) Solved

An encoded letter from J.E. Johnston to Robert E. Lee, dated 8 April 1862, is found at Civil War Day by Day. The image shows the recipient could not decode the message. Davidsch found the right dictionary, which led to the following reading (see another article).

There are 45R1(cars) here for 174R16(one) 40M10(brigade). 228L33(Six) more to 108L13(follow). 250R18(Three) of them, 153R22(Long-) 239L29(-street) will 157R17(march). Can not the government 195R11(procure) 45R1(cars) for the 176M23(other) 250R18(three)? I hope enough for 174R14(one) 40M10(brigade) will 56L26(come) to-morrow.

A Dictionary Code Used by Confederate Navy during the Civil War (1863)

An encoded letter from Lieutenant Barney, commanding CSS Harriet Lane, to Mallory, Secretary of State, remains unsolved. The dictionary is said to be a Webster (see another article).

Barney to Mallory, 19 March 1863
In my last of 9th instant by Lieutenant Warley I reported that General Magruder proposed to (177)-2-16- the (216)-1-15-(113)-3-85- in (29)-3-36-(23)-3-29. I am officially informed that (163)-1-34- will prevent (85)-3-14- from (115)-1-7-. As my previous suggestions are thus defeated, I presume the (262)-3-22- will not be kept in (54)-2-33, (215)-2-26 being entirely useless. I beg leave respectfully to suggest that being so near (149)-1-30-a (156)-1-8- the (163)-3-40 might be (213)-2-21-(10)-1-12-.
P.S. -- What shall be done with the (150)-3-12- sent from Richmond in case the above suggestion is carried out? Some might, if practicable, be sent (10)-1-12-.
N.B. -- The second or middle figure indicates the column, 1st, 2d, or 3d.

The highest page number in the message is 262 and the highest line (or entry) number is 85. The column is either 1, 2, or 3. While there are many dictionaries bearing the name of Webster (The Online Books Page), 3 columns and 85 lines (assuming the latter indicates an unmanipulated line number directly) almost limits the candidates to the unabridged with its most condensed format (for example, Webster's Handy Dictionary (1877) has three columns but only 64 lines). One may rather rely on the relative location of the coded words in the dictionary (see another article for illustration of such a method), with the help of the context found in OR Navy or other sources.

A Diplomatic Telegram from British Consulate in Africa (1911)

An encoded telegram from the British consulate in Lüderitz (Wikipedia) (then German South-West Africa (Wikipedia)) to the Foreign Office in London is posted in Klausis Krypto Kolumne. It consists of 43 five-figure groups: "68195 71235 ...."

Japanese Coded Telegram Decoded by Yardley (c. 1920)

It may be inaccurate to call this "unsolved" because it was probably solved by Yardley's Cipher Bureau at the time. It is printed in Yardley's The American Black Chamber (1931) p.251 as a typical example of Japanese displomatic code messages (though he does not say this was the first which he solved and demonstrated in the book). The sender appears to be Uchida Kosai, foreign minister from 29 September 1918 to 2 September 1923. See another article for various codes deciphered by Yardley and another article for details of one specific code dubbed Jp.

German Navy Enigma Messages (1942) Solved

The German Enigma cipher during World War II was broken by the Allies but three unsolved messages intercpeted in 1942 were found. Two of them were solved by distributed computing of Stefan Krah's M4 Message Breaking Project in 2006 and the last was solved by Dan Girard in 2013. CNET carries Graeme Wearden's report in 2009.

Another Enigma Message (1945)

A photo(!) of an unsolved Enigma message sent on 10 January 1945 by a deputy of "Oberbefehlshaber Oberrhein" (Supreme Commander of Upper Rhine Area) (to which the post Heinrich Himmler had been appointed in December 1944) is presented in Klausis Krypto Kolumne. This article also cites further works in recent years to break original Enigma messages from World War II. Another article of the blog reports reconstruction of Bombe.

©2015 S.Tomokiyo
First posted on 11 January 2015. Last modified on 21 March 2019.
Articles on Historical Cryptography

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