|Owners||Portland Protective Association|
|Appears||The Protector's War|
|Comments||This is an article about a fictional representation of an historical location, character or entity; please see the article about Ottendorf cipher on Wikipedia.|
The Altendorf substitution code was the name used by Samuel Aylward to describe a code based on both the sender and recipient have access to identical copies of a book and using numbers that referred to page, line and position in line of words in the book.
In The Protector's War, a group of refugees flees the Portland Protective Association. When found by Samuel Aylward and other Mackenzies, one of their members offers a list of codes. Sam describes them as "Altendorf substitution code" and describes how both parties using a cipher must have identical copies of the same book.
After the Mackenzies capture Mathilda Arminger and Juniper Mackenzie agrees to a visit by a delegation from the PPA, the group arrives during the horse fair at Sutterdown. Katrina Georges, one of Mathilda's tutors brings a book Mathilda wants to loan to Rudi Mackenzie. When Eddie Liu, who is leading the delegation sees the book, he is enraged.
That night Liu and his men attempt to rescue Mathilda and capture Rudi as a hostage to ensure their safe escape. Liu demands that his men finds the book Katrina brought. After the battle that follows, in which Rudi is gravely wounded, Mathilda confesses to Juniper that Rudi would not have been attacked if Liu had not wanted the book. Juniper realizes that the book is the key to the cipher.