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.