Rev. William Gordon's Polyalphabetic Cipher for George Washington (1786)

Rev. William Gordon (1728-1807) was born in England but went to America in 1770 and took up the patriotic cause. In 1788, he published a four-volume history of the American Revolution. (Founders Online)

Introduction of the Cipher

Before he left for England in early 1786 to complete his work, Gordon sent a cipher to George Washington for use in their correspondence.

Gordon to Washington, Jamaica Plain [Mass.], 4 February 1786
As I may possibly have something at one time or other to communicate, which I would wish to conceal from every one but yourself, I propose sending you a Cypher the next week, & if you approve of it let Cornwallis be the key, which keep secret in your own breast.
(Founders Online)

Gordon to Washington, Jamaica Plain [Mass.], 16 February 1786
Have drawn out the cypher (which I shall enclose) & given a specimen of the mode of working with it. To you it may have no novelty.
(Founders Online)

At the time, Washington had retired from public life but did not have much leisure because of numerous correspondences and other duties. He did receive the cipher but just laid it aside for the time.

Washington to Gordon, Mount Vernon, 20 April 1786
Your Cypher came safely to hand. I have not had leisure to examine it, but presuming no difficulty will arise in the use, I have laid it by 'till occasion may call it forth.
(Founders Online)

Gordon was justified in his precaution, as he recounted from England later in the year. He reported, among others, there were many falsehoods unfriendly to the United States and concludes with a warning:

Gordon to Washington, 28 September 1786
Would have your letter be under cover & directed by another hand, & sealed with another seal, that it may not be known at the Post Office that we correspond, lest the runners of government should suppress or peep into your letters. I have learnt, that one of the former secretaries gave me the name of arch-rebel, & that the letters in my hand writing were stopt.
(Founders Online)

Cipher Scheme

To the left of the table are instructions for enciphering (cipher numbers only partially transcribed below), while similar instructions for deciphering are to the right.

Supposing the key to be Boston then
B ostonB os tonB ost onBost onB ostonBost on Bosto I expect to sail for Europe the beginning of April 8,16,5,....

Where does B fall in with i? on the line 8 o .. with e? .. 16 s .. with x? .. 5 etc.
The trouble may be lessened by leaving out those words that the good sense
of the reader will not fail of supplying -- thus expect to sail beginning April.

This is equivalent to a variant of Vigenere cipher known as Beaufort cipher. The top row of the alphabet table shows key letters. Along the column headed by a letter in the keyword (e.g., "B"), the plaintext letter (e.g., "I") is sought and the figure far left in the row (e.g., "5") indicates the ciphertext letter. Use of figures for the ciphertext facilitates explanation of the scheme and may avoid confusion for beginners between plaintext and ciphertext letters as in ordinary Vigenere or Beaufort cipher.

Forgotten Cipher

It appears the cipher was never used. Gordon was not even sure of the keyword "Cornwallis" he proposed in the beginning.

Gordon to Washington, 3 April 1788
Should Cornwallis be the watch word agreed upon, of which I wish to be absolutely certain, be pleased to introduce it in your next.
(Founders Online)

Gordon to Washington, 24 September 1788
I send under cover to Mr Hazard, that so it should not be known at the Coffee house, that I correspond with your Excellency; & pray you not only to have any direction to me written in some other hand than your own, but the letter sealed with the seal of another. When you write again, introduce the Key in some sentence when it may appear natural, with a stroke underneath it. The reason of the request is, my not being absolutely certain about it, though I conceive it has some relation to the persons who surrendered at York Town.
(Founders Online)

Washington, in his part, could not even locate the cipher. After acknowledging the news of completion of Gordon's History and professing his desire to remain in private life (the Constitution of the United States, which had been adopted under the presidency of Washington in 1787, had been ratified earlier in the year and Washington was under pressure to take up public affairs again), Washington confessed as follows:

Washington to Gordon, 23 December 1788
As it is really so long since I have had any occasion to make use of a cypher or key to communicate my sentiments to my Correspondents; and as it was so little probable I should ever have any occasion to express them by such modes in future, I have absolutely mislaid or entirely lost yours, with others. Besides, I have not a single idea to communicate to any person while in Europe; the knowledge of which could give any advantage to those who should be curious enough, or mean enough, to inspect my letters. Thus much I thought it might be well to say, in apology for my not being able to comply with your request.
(Founders Online; George Washington Papers)