Decipherment of a German encrypted letter sent from Sigismund Heusner von Wandersleben to Axel Oxenstierna in 1637

We present our work on an encrypted letter from the Thirty Years’ War written by the ally of the Swedish Empire, Sigismund Heusner von Wandersleben in 1637 and sent from Kassel to the Swedish High Lord Chancellor Axel Oxenstierna. We describe our analysis of the ciphertext including information on the cipher type, the process of cryptanalysis and challenges for the decipherment. We include the edition of the letter in the current state of decipherment and summarize its content.