A Second "More Ample" Babington Cipher

Chapter 2 of Nadine Akkerman and Pete Langman (2024), Spycraft details on the undoing of Mary, Queen of Scots, in the Babington Plot and points out many facts which should have been apparent from well-known sources.

(1) The famous cipher used in Mary's fatal letter of 17 July 1586 to Anthony Babington was a very simple one. (The first letter from Mary to Babington dated 25 June 1586 (Pollen (1922) p.15) was also in the same cipher, as I noted in "Ciphers of Mary, Queen of Scots". The 17 July letter was a reply to Babington's response to this first letter.) When one learns that Mary used more elaborate ciphers with other correspondents (as seen in the collection of keys in SP53/22, SP53/23), one cannot help wondering why such a simple cipher was used in this important correspondence.

The authors point out (p.133) that new correspondents were given a simple cipher at first and a fuller one later. Indeed, the 17 July letter ends with "I have commanded a more ample alphabet to be made for you, which herewith you will receive" (cf. Pollen (1922), p.26 ff., esp. p.45).

According to the authors (p.138), such a "mature" cipher was actually used by Babington in his reply dated 3 August 1586 (Pollen (1922) p.46-47, printed from SP53/19 no.10), but the key was intercepted by the authorities and the letter was readily deciphered by Phelippes. Phelippes attests "The new Alphabet sent to be used in time to come between that Queen and Babington ... is of Nau's hande" (I have not checked the cited SP53/19 no.85, which is Phelippes' record of the secretaries' testimony from 4 September, to see whether "in time to come" really refers to the 3 August letter).
[(8/14/2024) Nau's argument is printed in Tytler's History of Scotland. It says "The new alphabet sent to be used in time to come between that Queen and Babington, accompnying the bloody despatch, is of Nau's hand." So the cipher was attached to the 17 July letter (consistent with Mary's wording "herewith") and it may well have been used in the 3 August letter. Curle's cover letter to Barnaby enclosing the 17 July letter says "Giuen hereiwth is the addition to this alphabet" (Pollen (1922) p.25). If this does not refer to an update to the Mary-Babington cipher, such an update may well have been enclosed at the same time.]

(2) Another observation of the authors interesting from a cryptologic viewpoint (p.134-135) is that the well-known copy of the Mary-Babington Cipher in SP12/193/54 is a copy from the original, rather than a product of Phelippes' codebreaking. This can be seen from the nomenclature entries such as "your name" and "myne."

On the other hand, before concurring with the authors' conclusion that Phelippes did not break the Mary-Babington cipher at this time because he already had the key, we may need to assess whether it was feasible to associate a particular intercepted key to Babington (for example, if the three keys on SP12/193/54 were the only keys sent out around June 1586, the authentic key could have been used by Phelippes).