The author published an 17-page article on this subject in 2022, entitled "The secret service of renaissance Venice: Intelligence organisation in the sixteenth century", which seems to have been the basis of this book. It can be found here:
https://radar.brookes.ac.uk/radar/items/3d669bd8-c10c-4436-9...
(A link to the PDF can be found under "Attached files".)
I found this through the list of publications on her web page: https://www.brookes.ac.uk/profiles/staff/ioanna-iordanou
She also has another related paper:
"The Professionalization of Cryptology in Sixteenth Century Venice"
https://radar.brookes.ac.uk/radar/items/d6c33ee2-34c8-4994-b...