Letters she sent were decoded at the time. The evidence leading to her being executed was largely based on that. It is a simple substitution cipher so vulnerabl

Letters she sent were decoded at the time. The evidence leading to her being executed was largely based on that. It is a simple substitution cipher so vulnerable to letter frequency analysis. So the article title is either misunderstanding or click-bait. They do appear to have found previously lost letters which is very interesting. But deciphering them is easy.