Two Syllabic Challenges (1653, 1654)

The volume I mentioned yesterday (ADD MS 4200) includes two letters that appear to be undeciphered: a letter of Bordeaux, French ambassador in London (1653) and a letter of the Prince of Condé (1654). I included sections for these in "Unsolved Historical Ciphers".
Both employ Arabic figures with diacritics and probably involve symbols representing syllables.

The ambassador's cipher would be similar to other French diplomatic ciphers having fairly regular assignment of syllables to numbers.
The Prince of Condé was in the Spanish Netherlands and fought the French at that time. If his cipher in 1654 was similar to the known cipher from 1655, it would involve non-trivial assignment of syllables to numbers.

The Prince of Condé's Cipher with his Agent in London

The cipher used in the correspondence from 1655 between the Prince of Condé and Barriere, his agent in London, (Add MS 4200) is better than contemporary French ciphers in that single letters, syllables, other words and names, and nulls share diacritics. For example, single letters may be represented by figures with a circumflex (^) or an umlaut (¨) (or other symbols based on Roman letters), while some syllables and words are also represented with figures with a circumflex or an umlaut.
At the time, Condé was in exile in the Spanish Netherlands and was fighting the French troops. It may be speculated that he might have had his source of cipher other than the king's court.
See the new section in the updated article, "Ciphers Early in the Reign of Louis XIV".

A Syllabic Cipher of Cardinal Gualterio Reconstructed Manually

I uploaded a new article "A Syllabic Cipher of Cardinal Gualterio Reconstructed Manually (ca.1715)", in which I demonstrate manual reconstruction of symbols representing syllables used in letters of Abbé D'Estées, given assignment of symbols for single letters.
The letters record real-time reactions to historical events such as James Edward's expedition to Scotland (December 1715), Prince Eugene's victory over the Turks (August 1716), Spanish invasion of Sardinia (August 1717), and the Triple Alliance (January 1717). Actually, these are mentioned in cleartext. Hopefully, the ciphertext contains even more interesting contents. (I don't know whether the plaintext is in the archives.)

Parliament's Ban on Ciphers during the English Civil War

Use of cipher was prohibited during the English Civil War by an order passed by the Parliament in April 1643: "That all such should be punished as Spyes and Enemies of the State, who hereafter should send any Letters or Papers written with Cyphers, or any other unknowne Characters." (Nadine Akkerman, "Enigmatic Culture of Cryptology" in Daybel et al. (ed.) (2016), Cultures of Correspondence in Early Modern Britain).

But the ban was only selectively enforced, at least in the view of the royalists. The Mercurius Aulicus (21 October 1643), a weekly royalist news pamphlet, accused the parliamentarians of the partisan application of the rule and printed an intercepted cipher letter subscribed by a Parliamentarian, a Matthew Durbun, pointing out that the parliamentarians "when they please can practice it, without the least transgression of their order, which it seems was made only for the punishment of the Kings friends but not for such innocent Rebels as they are."

How long the ban was in effect is not known for sure. While it was natural for the royalists to continue using ciphers (see "King Charles I's Ciphers"), we know that under John Thurloe (head of intelligence from July 1653), informants used ciphers (see "Codes and Ciphers of Thurloe's Agents"). Akkerman points out John White's A Rich Cabinet with Variety of Inventions (1653) promoted use of cipher when writing love letters and John Cotgrave's The Wits Interpreter (1655; 1662; 1671) described one of Cardinal Richelieu's cipher keys and recipes for secret ink. By these days, ciphers as well as steganographic techniques such as secret ink became quite common even among ordinary people.

Duke of Nevers' Variable-Length Figure Cipher (1571)

From my renewed interest in variable-length figure ciphers I mentioned the other day, I uploaded my transcription of a ciphertext from an undeciphered letter in Italian from Lodovico Birago to the Duke of Nevers (1571) in "Unsolved Historical Ciphers".
Although the ciphertext is relatively short, once the continuous stream of figures can be broken into tokens (cipher symbols), homophonic solvers may readily decipher this.