Decoding Deane-Jay Code

Silas Deane was sent to France by the Continental Congress early in 1776 as a secret agent to seek French assistance to the colonists. Soon he was joined by Benjamin Franklin and Arthur Lee. However, his financial transactions aroused suspicion from Lee. Eventually he was recalled and returned to America in 1778.

In a dispute before Congress, he was defended by his friends including John Jay. With the accusations unsettled, he was allowed to return to Paris. Thus, he left America in June 1780 and arrived at Paris for the second time in July 1780.

The year before, John Jay had been appointed as minister to the Spanish court. When Jay left in October 1779, Deane had given him a code THE=780 (mentioned in Deane to Jay, 8 September 1780).

The code had a vocabulary of about 900 words generally arranged alphabetically, e.g., 1(a), 780(the), 867(your). Conjugated forms and derivatives are usually represented by a single code, e.g., 43(arrival/arrived), 675(resolution/resolve/resolving) but the ending is sometimes hinted by a suffix 270g(establishing), 410g(increasing), 675g(resolving), 843d(wanted), 344n(given).

Since the code did not contain single letters or syllables, only the words in the code list could be encoded. Sometimes, a letter was appended to a code to denote another word: e.g., 1s(as), 780m(them). Usually, however, words not in the code list had to be enciphered by a substitution table. It was a simple Caesar cipher. That is, a letter was enciphered with a letter which is next in the alphabet.

plaintext: a b c d e f g h i j k l m n o p q r s t u v w x y z ciphertext: b c d e f g h i j k l m n o p q r s t u v w x y z

Numbers could also be enciphered by alphabetical letters:

plaintext: 1 2 3 4 5 6 7 8 9 0 ciphertext: a b c d e f g h i j

In order to distinguish the enciphered letters from ordinary words, enciphered words were often underlined and enciphered numbers were marked with a double underline.

The code was used at least from 18 September 1780 to 16 June 1781. (According to Jay Papers, a letter from Deane to Jay dated 1 December 1782 is accompanied with a sheet in cipher, which may be the same code.)

Most of the passages in code of the Deane-Jay correspondence in Jay Papers have interlined decoding but some are left undecoded. Further, interlined decoding is often truncated. For example, the interlined decoding "am" for 31 actually meant "America" or "American".

From encoded passages with interlined decoding, we can partially reconstruct the code list, which may be used to decode yet undecoded portions.

Deane to Jay, 18 September 1780

... whilst France establishing an army on the continent & affording us no decisive aid but holding the [balance] between England & America & between the parties in the latter, America will be so reduced, as well as England that the last may be left to its fate without the least apprehensions of future events.

(Page 10)
... whilst 311(France) 270g(establish[ing]) 3(an)
42(army) 569(on) 780(the) 188(contin[en]t) 62(&) affording 825(us) 534(no) decisive aid
114(but) holding 780(the) 72(Ball [balance]) between 266(Eng[land]) 62(&) 31(am[erica]) 62(&) between
780(the) 601(parties) 394(in) 780(the) latter, 31(am[erica]) 855(will) 68(be) 710(so) 664(reduced), as well
as 266(England) 816(that) the last may be left 799(to) 398(its) gbuf[fate] without the
least apprehensions of 321(future) 274(events).

Jay to Deane, 2 October 1780

Had Harding arrived before you left Philadelphia? Send your letters under cover to some person here. They may then come safe. Carmichael cannot account for Bancroft not answering his letters.
When we write in cypher for the future, add 20 to each number.

Had Harding(ibsejoh)⁽¹⁾ arrived⁽²⁾ before you left Philadelphia? send
your letters under cover to some Person here. They may then come
safe[.] 185[Carmichael]⁽³⁾ 121(cannot) 15(acc[oun]t) 284(for) 71(B[ancroft])⁽⁴⁾ 535(not) 36(an[swering]) 369(his) 471(letters) [one word? unreadable] --
852(when) 848(we) 857(write) 394(in) dzqifs(cypher) 284(for) 780(the) 321(future) bee(add) bj(20) 799(to)
256(each) ovncfs[number].

(1) Rather than cipher "ibsejoh" with an interlined plantext "Harding", the cipher "ibsejoh" is written above the plaintext. This word is substituted for struck out words "the Confederacy" with an interlined code "139" (not struck out). Seth Harding was Captain of the ship Confederacy which Jay was on board when he sailed from America. Jay mentioned Harding probably because Harding was a witness of the feud between Jay and Carmichael which started soon after they left the American coast. (See, for example, a letter from Jay to Deane dated 16 June 1781 below.)

(2) This word is also a substitute for some struck out word with an interlined code "101" (not struck out).

(3) The code 185 is consistently left without interlined decoding. From the partially reconstructed code list, which is generally alphabetically ordered, it may safely be said this is a name starting with C. The identity "Carmichael" may be conjectured from Deane's reply to this letter (see below).

(4) The interlined decoding for the code 71 is consistently abridged as "B". Again, "Bancroft" may be conjectured from Deane's reply to this letter (see below).

Deane to Jay, 16 October 1780

This is a reply to Jay's letter of 2 October. Jay's proposal to change the code by adding 20 to every code number was not understood by Deane. Thus, both continued to use the original code prepared by Deane.

Ct [Captain] Harding arrived before
I left Virginia but I left Philad[elphi]a soon after you. my
Letters in future will come under Cover as you advise. --
Dr Bancroft can best account for his not answering Mr.
Carmichael[']s letters, tho from what the Doctr has told
me, I am surprised that the latter should be at any
loss at all on the subject. I do not well understand
your proposed addition of bj(20), & therefore must write in
my former method untill you explain it more fully.

In a subsequent portion of the letter, Deane enciphered "common sense" as "bpllpo tdotd", which actually should be "dpnnpo tfotf".

Jay to Deane, 27 October 1780

Your favor of the 9th Inst. has come to my hands having as usual been inspected. Spain wants Mississippi. Sat verbum. Whenever you write to me, do it in full expectation that your letter will be opened before I get it, this being the case with almost all I receive. The language of our minister J.Adams will never do. If your suspicions prove true, excuses will be drawn from every little circumstance capable of affording the most trifling

Your favor of the 9th Inst. has come to my hands havg
as usual been inspected - 738[Spain] 843[wants] 520[Mississippi] sat verbum
whenever you write to me do it in full expectation that your letter
will be opened before I get it, this being the case with almost
all I receive. The language of 586[our]
512[minister] 53[J.Adams] 855[will] 536[never] 198[do] - if your suspicions prove true, excuses
will be drawn from every little circumstance capable of affording
the most trifling

Deane to Jay, 1 November 1780

~~Your having left Philadelphia when you did accounts for your not knowing certain matters which you otherwise would have done and which would have explained my remark relative to Bancroft & Carmichael.~~
....
~~My question about Bancroft & Carmichael was not with his privacy or by his request. Nor shall I make the least mention of your remark on that stead.~~
....
In my last, I told you that Spain wanted Mississippi. A sheet could not convey more to a person so well acquainted with the subject as you are.

Your having left Philadelphia when you did accounts for
your not knowing certain matters which you otherwise
would have done and which would have explained my
remark relative to 71[Bancroft] 62[&] 185[Carmichael]
[The above paragraph is crossed out.]
....
487(my) 655(Qu[estion]) 7(ab[out]) 71(b[ancroft]) 62(&)
185[Carmichael] was not with 369(his) 624[private]y 571(or) 115(by) 369(his) 683(Req[uest]) nor shall I
make the least mention of your remark on that stead
[This portion is also crossed.]
....
In my last I told you that 738[Spain] 843[want]d 520[Mississippi]
a sheet could not convey more to a person
so well acquainted with the subject as you are

Jay to Deane, 28 March 1781

[Postscript]
The reason why I think if you mean to come this way, you had better do it soon is that you may soon [maintain??] successor with whom more may perhaps be [done?] by a time -- [invaluable?] than any other money.

The reason why I think if you mean to come this way, you had better do it
soon, is, that you may 712[soon] 488[maintain??]⁽¹⁾ tvddfttps[successor] 856[with] xipn[whom] 530[more] may perhaps 68[be]
197[done?]⁽²⁾ 115[by] 1[a] 815[time] -- 426[invaluable?]⁽³⁾ 789[than] any other 515[money] --

⁽¹⁾ Reading not supported by another instance. The sequence of known code numbers suggests this is probably a word beginning with an "m" before 493(many) and possibly the first word in the "m" section apart from 485(me), (mine?), and 487(my). Another candidate may be "manage".

⁽³⁾ Reading not supported by another instance. Guessed from 432(interest) and 430(island).

Jay to Deane, 16 June 1781

As to Carmichael, he is ignorant of the subjects of any letter that have passed between us. He [once] had my good opinion and might have [retained] it if almost from the time we sailed from America he had not given me [sufficient] [case] to repent his being with me. [I] cannot now go into details, I wish to be in a situation of forgetting them & him. This must be entre nous.
I am told that Payne is in France, but as far as I can learn, the objects of his voyage remain a secret.

1[a]s 799[to] 185[Carmichael] 368[he] 396[is] 399[ignorant] 576[of] 780[the] 762[subject] s 576[of] any 471[letter] 816[that] 373[have] 602[pass] d cfuxffo[between] 825[us] 368[he]
poef[onde]⁽¹⁾ had 487[my] 345[good] Pqjojpo[Opinion] 62[and] njhiu[might] 373[have] 678d[retained]⁽²⁾ 398[it] 397[if] almost 316[from] 780[the] 815[time] 848[we] 716d[sailed]
316[from] 31[America] 368[he] had 535[not] 344[give] n 485[me] 754[sufficient]⁽³⁾ dbuf[cate]⁽⁴⁾ 799[to] sfqfou[repent] 369[his] being 856[with] 485[me] K[I]⁽⁵⁾ 121[cannot] 559[now] 332[go]
395[into] Efubjmt[Details] J[I] xjti[wish] 799[to] 68[be] 394[in] 1[a] Tjuvbujpo[Situation] 576[of] gpshfuujoh[forgetting] 780[the] m 62[&] ijn[him] -- This
must be entre nous --
I am told that 604[pay]n⁽⁶⁾ is in France, but as far as I can learn, the objects of his
voyage remain a secret.

⁽²⁾ Reading not supported by another instance. Guessed from 675(resolve/resolution) and 682(regard). (This part of the code list is out of alphabetical sequence.)

⁽³⁾ Reading not supported by another instance. Guessed from 753(suffer) and 756(supply).

⁽⁵⁾ Context suggests this "K" is a cipher for "I", though Jay uses "J" for the word "I" in the next line. He may have identified "i" and "j" here.

⁽⁶⁾ Reading not supported by another instance. Guessed from 602(pass) and 605(peace). Thomas Payne was in France from March to May 1781, accompanying young John Laurens to seek immediate French aid.