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.
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 undeciphered.
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.
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.
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.
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.
I solved in 2019 a cipher used in a letter addressed to Cardinal Schiner (1520), only to find that it had already been solved by Grégoire Nicollier, Matthieu Jacquemet, and Gilles Evéquoz. The cipher is a simple numerical cipher, but it is interesting in being an early specimen. See another article.
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.
Undeciphered letter of 1551 (PARES)
Undeciphered letter of 24 August 1551 (PARES)
For contemporary Spanish ciphers, see another article.
The letter (PARES) is undeciphered. The cipher looks like (but, of course, not the same as) Cg.6 (1571). (For Spanish ciphers at the time, see another article.)
Of many unsolved ciphertexts of which keys have been found (by myself or others), only some are given in this article. I specifically mention BnF es.132 here because it may contain interesting materials for historians. It includes many undeciphered letters from Philip II and Antonio Perez to Juan de Vargas Mexia. The keys were not known at least as of 2012. In 2020, I identified the four keys used in this volume (I cracked one myself). This will allow historians to read the letters in the volume. See another article for details.
BnF fr.20974 is a collection of ciphers used in the correspondence of the Duke of Guise (ca.1556). It includes some undeciphered ciphertexts. I solved one cipher, but two remain unsolved. See another article.
I posted undeciphered letters to Mr de Mercoeur probably from the Duke of Guise in my blog.
For contemporary ciphers, see another article, which also presents several other undeciphered ciphertexts, including the one below.
A private email made me aware of three new Vatican challenge ciphertexts posted by George Lasry in 2019 at MTC3:
The Vatican Challenge - Part 3 ... a short message dated "Brusseles 9 Oct. 1721", consisting of one- to four-digit figures.
The Vatican Challenge - Part 4 ... a letter from the bishop of Senigallia to the Secretariat, consisting of figures. The cleartext seems to include the date "Marzo 1536." This was solved in August 2019 by Thomas Bosbach, who found a matching plaintext in a book (Lasry et al., "Deciphering papal ciphers from the 16th to the 18th Century" (Cryptologia)).
The Vatican Challenge - Part 5 ... The cleartext seems to include the date "Aprile 1542." According to the introduction of the challenge, this letter is in a bundle of "Lett. Orig. e cifre del card. Farnese al nunzio, 4 oct 1539-24 nov. 1548. ff. 7-123."
See my blog for some observations.
Two ciphers of papal nucios (1625, 1628) were posted as challenge problems at MTC3 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
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).
BnF fr.4715 in the French archives contains many undeciphered letters. I could solve some (at least partially) but three remain unsolved despite their seeming simplicity. See another article.
BnF fr.4712 contains some undeciphered letters. 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)
Cinq Cents de Colbert 33, a volume containing despatches deciphered by Viete, contain some undeciphered original letters apparently left undeciphered by Viete. See another article.
(f.539) Cardinal de Joyeuse to Villars, admiral de France, Rome, 15 February 1594
(f.555) Senecey to Archbishop of Lyon
Ms. 994 of National Library, Madrid, contains an undeciphered letter from Venetian secretary Marco Otthobon [Marco Ottobon] to ambassador, Juan Mocenigo [Giovanni Mocenigo], dated 27 April 1589. Valle de la Cerda appears to have solved it, but his solution is lost. See another article.
BnF Clair 369 (Gallica) contains a partially enciphered letter dated Rome, 13? November 1616 from Cocquet to Mangot (f.316). See another article for some contemporary ciphers.
Ms. 994 of National Library, Madrid, contains ciphertext solved by Luis Valle de la Cerda. The cipher was in a scheme invented by a Milanese, Jerónimo Sertori. Valle not only broke it but indicated that he had devised the same scheme fifteen years earlier. However, his solution is not extant. See another article. (According to Nick Pelling's blog ("Girolamo Sirtori Cipher Mystery"), Eloy Caballero got close to the solution in 2012.)
A letter of fra Guglielmo Vizani, 8 October 1637, has portions that appear to be in an unsolved cipher. See another article.
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 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 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.
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.
Cardinal Richelieu's letter from 1641 mostly in cipher was solved by Norbert in 2020 (Klausis Krypto Kolumne). See another article for some background.
An unsolved letter from Henri Brasset, a French resident in The Hague, to "Vostre Eminence" (Mazarin?) is in BnF Clair 421. The figures with diacritics probably represent syllables alphabetically arranged and some words and names, as with other ciphers at the time (see another article). You can post comments or solution in my blog, where I posted my provisional transcription and initial comments.
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.
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.
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.
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's letters in cipher during his captivity in the Isle of Wight (1648) remain undeciphered. See another article.
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.
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).
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.
Some passages in cipher in Charles II's letter to the Duke of Hamilton (1650) remain undeciphered. See another article.
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.
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).
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)
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).
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.
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.
A coded letter of 1691 addressed to General Catinat appears to remain unsolved (see another article).
A coded letter of 15 September 1702 written by Marshal Catinat remains unsolved (see another article).
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:
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.
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 devised a new cipher system and sent Thomas Jefferson a challenge, which was deciphered in 2009 by Lawren M. Smithline. See another article.
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.
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.
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.
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.
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.
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).
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).
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).
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.
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 ...."
An undecoded telegram to Sun Yat-sen (1916) is preserved in the Japanese archives. For the most part, it consists of ten-letter groups. It seems certain that the message was first encoded with a conventional Chinese telegraph codebook, and then two-digit figures were translated to two letters (consonant+vowel) with a code condenser.
Another article presents two contemporary code condensers used by Junzaburo Yamada, who supported Sun Yat-sen, and also provides my decoding of Sun Yat-sen's telegrams, which were superenciphered by addition of 111 instead of using a code condenser.
The Japanese found out the superencipherment, but it is not known whether they identified the code condenser. A clue may be found from the fact that the typical Chinese codebook at the time did not have the figures in the 9000s.
The Japanese archives preserves a telegram from Huang Xing to Lin Hu and Li Genyuan (1916). They were in exile in Japan, and opposing Yuan Shikai separately from Sun Yat-sen.
The syllable structure is different from Sun Yat-sen's code condenser above. Actually, the syllables (no Cs or Ls, SHI, CHI instead of SI, TI) conform to the Japanese syllabary. There remains a possibility that the enciphering is something different from a code condenser.
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.
In 2008, the Zhongshan Warship Museum called for solution of encrypted telegrams found in SS Zhongshan, which was sunk by the Japanese bombing in 1938. As of 2009, 352 out of 891 were solved. I have not located the primary sources of these telegrams. See another article.
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.
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 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.