Mathematician Charles Babbage had an interest in cryptography and one volume of his papers is "Scientific Papers: 1. On cyphers and decyphering; 14. April 1808 - 12. February 1870" (British Library (BL), Additional Manuscripts (Add. Ms.) 37205, ff.1-303) (Franksen p.301).
The volume includes a worksheet "Letter of Henrietta Maria, Queen of Charles I, deciphered by C.B., July 1858" (title page, f.220) (Franksen p.34, correcting Kahn's reading "1850"), which is a transcript of the beginning of a letter wholly in cipher from Henrietta-Maria to Charles I, with interlinear decipherment.
The cipher used is what I call "the Third Cipher between Charles I and Henrietta-Maria" in another article. The original cipher is in BL Add MS 72438, f.67-68 (DECODE R8687).
The ciphertext with the deciphering (which I occasionally edited) is as follows.
In the blank half of the page to the right, there is a scribble "At fol. 32 part of another letter dated Paris, Decem. 8 or 9, written partly in English in same cipher / there appear several triplets [i.e., three-digit codes] translated as below". However, the fragments quoted in Babbage's note (e.g., "of Q:R:[the Queen Regent] ... of money to be able to", "money and arms to his majesty") are actually in a continuation by Jermyn of an earlier incomplete letter of the Queen, 11/21 November 1644 (Green p.267-268) in the version in print edited by Green. In Harl. 7379 f.32, the text suddenly switches from French to English in the middle of this page. Probably this is the case Green called "the copyist having proceeded with an entirely different letter, as though it were a continuation of the same" (p.vi).
It is noted that the cipher used by the Queen in her letter in French is also used in English by Jermyn. Henrietta-Maria used the cipher prepared for English in her French letters, as I once observed in another article for "Cipher between Charles I and Henrietta-Maria (and Ministers) after Naseby (September 1645)".
Babbage tells us in a letter (see below) that he "made out much of two of the cyphers" at the library in the British Museum. That is, he reconstructed at least one other cipher than the above, possibly by using deciphered letters available in the library.
While Babbage seems to have achieved these independently, there is also evidence that he was later supplied with materials from a historian, Everett Green. While Babbage's note mentions "the formation of the key" by using the original letters "carefully deciphered" in the state paper office, most probably this refers to the work by Green (see below). (cf. Franksen p.36-38; Kahn p.205)
In 1858, Babbage exchanged letters about ciphers of the royal couple with a historian, Mary Anne Everett Green (Wikipedia), who had compiled Letters of Queen Henrietta Maria (1857).
It appears that Babbage sent an inquiry to the historian, enclosing unsolved ciphertext ("your cyphers"). Green found her keys did not fit and let Babbage try himself.
From Babbage's reply below, it appears Green provided him with three or more keys she reconstructed, of which two were ones Babbage reconstructed independently from the materials at the British Museum, but Green's papers provided identification of additional triplets (three-digit codes).
The letter also mentions a book project about codebreaking (see also Franksen p.13-16, 34).
The unsolved cipher in question here would not have been the cipher of the above-mentioned Queen's letter in Babbage's worksheet, given that Green not only knew this cipher but also the plaintext of the letter itself. The last two letters suggests it was an unsolved letter of Charles I. (Babbage's reference to Charles II must be an error for Charles I, as pointed out by Green, given that his note of the ciphers refers to "Letters of Henrietta Maria & charles II" (see below), which is obviously an error.)
Specifically, the unsolved cipher letter in question might have been Charles' secret letter to Goffe (Franksen p.38 also makes this connection). It is known that this puzzle was brought to Babbage this year but he declined to be engaged in it and in June 1858, the matter was brought to Sir Charles Wheatstone (see another article). From this timeline, Babbage might have sought a solution after he declined to take up the problem.
Another question is what was the present Babbage sent to Green, described as "a work on another subject" by Babbage and accepted as "a memorial of your indefatigable labours" by Green. Identifying this as the decipherment of Henrietta-Maria's letter above (Franksen p.34) seems unlikely, because the cipher and the letter were both known to Green. Although it is still possible that Babbage presented some other decipherment which he believed was new to her, it may have been some writing on a subject other than cryptography.
Babbage's note (f.110) summarizes four ciphers between Charles I and Henrietta-Maria used in 1642-1645, which are:
•First Cipher between Charles I and Henrietta-Maria (Feb. 1642-Aug. 1642)
•Second Cipher between Charles I and Henrietta-Maria (Aug. 1642-Jul.1643)
•Third Cipher between Charles I and Henrietta-Maria (Summer 1644-June 1645)
•Private Cipher between Charles I and Henrietta-Maria (1645)
which I described in another article (based on Green (1857)).
It can be seen that the main part of Babbage's note is textually identical with the description in Green's preface. I think Babbage made his summary from Green's description, rather than he provided Green with his analysis and the latter elaborated on it. (First, the exchange between them quoted above sounds as if Babbage first contacted Green after the publication of the book. Moreover, use of the verb "close" seems to be favoured by (though by no means unique to) Green (cf. p.302 "With this letter, closes the interesting series of private letters ..." p.337 "the political portion of the correspondence of Henrietta Maria may be said to close".)).
The following presents the description of the ciphers by Babbage and Green.
| Babbage Papers | Green (1857) |
|
(Harl. 7379 f.110) Mss in Harleian Colln Brit. Museum Letters of Henrietta Maria & charles II [sic] 90 folios Keys compiled from the decyphered passages a 2n 3rd, & 4th Cypher in three years 1 Cipher March 1642 1st Alphabet exprd by figures or symbols small words by combination of figs and letters proper names by pseudonymes 1st Cipher closes 18 aug 1642 2nd Cipher Entirely of figures except the smaller words, in which the compound of figures and letters used in the first are repeated occasionally The single letters and blanks occupy from 1 to 77 The higher numbers up to 339 are devoted to proper names which follow each other in Alp.l sequence as to initials only 2nd Cypher used untill spring of 1643 and afterwards with the Duke of Newcastle much of the original in the Harl. Mss. 3rd Cipher commences in the summer 1644 3rd Cipher a sheet of figures More comprehensive than the former includes a large range of Words [and] parts of words in frequent use Single letters & blankes occupy numbers to 80 thence to 322 names of persons & places upwards as high as 574 words of present recurrence The originals of these letters exist in the state paper office and have ma terially assisted in the formation of the key as they are all carefully deciphered 4 Cipher began Ap. 1645 |
The first cipher, concerted between them before they parted, was planned with much ingenuity. The alphabet is expressed by figures or symbols, small words by a combination of figures and letters, and proper names by pseudonymes; in order better to mislead any unwary intercepters of letters, the king and queen, and their confidential adherents, assumed the names of the principal leaders of the opposite party, as Pym, Hampden, Essex, &c. This portion of the correspondence has proved the most embarrassing, as in no one instance is the decipherment of any of these proper names given; the pseudonymes were evidently too familiar to the correspondents to require it. The true names are supplied from careful consideration of the parties and circumstances, sometimes with certainty, sometimes conjecturally with queries, when I was not quite satisfied about the correctness of my conclusion. The first cipher closes with August 18th, 1642, when for fear of discovery, it was thought advisable to adopt a second. This consists entirely of figures, excepting the smaller words, in which the compound of figures and letters used in the first
are repeated occasionally. The single letters and blanks occupy the number 1 to 77, and the higher numbers, up to 339, are devoted to proper names, which follow each other in alphabetical sequence, as regards the initial only, with a few simple words interspersed, and such as were likely to be frequently required. This cipher was used between the king and queen, until Henrietta's return to England, in the spring of 1643, and afterwards in the correspondence between her and the Earl of Newcastle, much of which exists in the original, in the Harl. MSS. In the summer of 1644, the queen again left England, and now a much more elaborated cipher was deemed necessary. The crisis of affairs had become so important, and the letters of the royal pair were so eagerly watched for, that it was thought advisable not to blend the cipher with the ordinary character as was before done, but to send the letters in the form of a sheet of figures, without date, or signature, or any clue, by handwriting or otherwise, to the writer. On this account, the cipher which is on the same principle as that last described, is much more comprehensive, including a large range of words, and of parts of words in frequent use, so as to diminish as far as possible the labour of using it. Single letters and blanks occupy the numbers up to 80, thence to 322 names of persons and places, and upwards as high as 574, words of frequent recurrence. The queen's portions, on account of her delicacy of health, were generally put into cipher by her constant attendant Lord Jermyn, and his lordship used the same cipher in a correspondence which he carried on, under the queen's direction, with Dr. Goffe, her agent in Holland. The originals of these latter letters are preserved in the State Paper Offic, and have materially assisted in the formation of the key, as they are all carefully deciphered. The last cipher came into operation as late as April 1645, just before the closing of this portion of the correspondence, and was only used on very few occasions, when the king and queen had some point on which they wished to disclose their sentiments to each other, without the cognizance of even their closest adherents. |
It is well-known Babbage solved a letter from Henrietta-Maria to Charles I, but it is less known that he received materials on the ciphers used by the royal couple from historian Everett Green, though it appears true that he achieved his solution independently. Still, the summary of ciphers in his papers was taken from Green's work.
Franksen, Ole Immanuel (1984), Mr. Babbage's Secret (Internet Archive)
Mary Anne Everett Green (1857), Letters of Queen Henrietta Maria (Internet Archive, Google; a contemporary review: Littell's Living Age (July, August, September 1857) (Google) p.285)
S.Tomokiyo, "Charles I's Cipher Revealed: Sir Charles Wheatstone's Codebreaking" (Cryptiana)