Saturday, June 4, 2011

Dr Church's Monoalphabetic Cipher

  So just what cipher did Benjamin Church, Jr. use in his letter to John Fleeming, his brother-in-law? He used what is referred to in cryptography as a "monoalphabetic cipher" -  a simple substitution code that uses fixed substitution over the entire message as opposed to a "polyalphabetic cipher" that uses a number of subsitutions at different times. Here is the key to Dr Church 's cipher:

The top line is the alphabet. The second line sets forth the substitutions  in Church's handwriting. The third line is a cleared up version of the second line.

 Here are the first few lines of the letter in original manuscript form:


   Here is the first page of the letter after being cleaned up to make it more readable:

      Using the key we get the first two sentences of the letter:

      I hope this will reach you. Three attempts have I made without success in effecting the last.


  1. This is really cool! Did you actually get to see/handle the original document in Church's handwriting?

  2. Thirty years ago I could walk into the Madison Building of the Library of Congress, walk into the room where the papers of George Washington are stored and ask to see the originals of the Washington papers. I would have to check my briefcase, etc., and walk into the room only with a lead pencil and sheets of paper. I would be issued a pair of white gloves and a librarian would bring the document(s) I wished to see. So, I did see and examine the original Church letter.
    Today, with all of the new rules and procedures in effect, I would have to provide the Library a specific reason why I would need to see the original Church letter. Since the letter is on microfilm, albeit a lousy copy made by an old and inferior technolgy, my request would be denied.
    But then I still remember the days when anybody could walk into a federal building in DC without being screened or pawed over by a bored security guard and just proceed to whichever office he needed to visit.
    And I can still recall the thrill I had actually handling the original papers of George Washington.
    A lost America!