19/03/2024

Codebreaking of Sir Robert Southwell during the Popish Plot

The Popish Plot may refer to "a period of extraordinary political tension that took hold in England in 1678" (Fictitious treasons: 'The Popish Plot') instigated by revelation of a fictitious plot known by this name.
My notebook included a reference to Sir Robert Southwell's deciphering during this period since 2009, but I have not known whether this involved codebreaking or used a key obtained in a non-cryptographical way. The other day, I found Southwell himself wrote this was "without a key", which makes it interesting enough to be included in an additional section in "Ciphers of Coleman's Correspondence Discovered in the Popish Plot".
It's a pity it is not known specifically what cipher was broken by Southwell.

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