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We Have a Winner in the Armstrong-Madison Encrypted Letter Contest!

Long term AFIO member Yaacov Apelbaum has successfully decrypted the Armstrong-Madison letter!  Mr. Apelbaum is a New York–based former intelligence officer with a deep background in signals analysis and cyber operations. Now active in the private sector, he focuses on cyber intelligence, counterintelligence, and counterterrorism support. An AFIO member since 2018, Apelbaum continues to advance the mission of U.S. intelligence through outreach, research, and operational consulting.

Below is the Decrypted Text (Letter from John Armstrong to President James Madison, 20 February 1808):

"The petitions of your seamen concerning their treatment have been examined. The French government has declared that American ships must not enter its ports. I have written to you before on this subject, which deeply affects our shipping and commerce. The ministry has given no assurance that, in relation to our neutral shipping and commerce rights, we shall receive satisfaction."

About the Letter:

This letter from Secretary of War John Armstrong discusses grievances regarding the French government's refusal to respect American neutral rights, specifically as they pertain to shipping and commerce. It reflects the formal diplomatic tone used in early 19th-century correspondence and is consistent with known letters from Armstrong in 1804 and 1806.

Codebook:

A code-to-word table is below, identifying unique numeric entries and their corresponding decoded English words or phrases. The cipher used appears to be a word-based diplomatic codebook, typical of early American state correspondence.

Verification Methodology:

To ensure the integrity of the decryption, a multi-phase verification process was employed. First, internal consistency was evaluated—each decoded sentence was assessed for grammatical structure, coherence, and stylistic alignment with early 19th-century diplomatic correspondence. Second, the decoded content was cross-referenced with known letters from John Armstrong (dated July 1804 and June 1806) to confirm thematic and linguistic parallels, particularly in the use of terms like “ministry,” “assurance,” and “neutral rights.” Third, a frequency analysis was conducted to confirm that high-frequency cipher values corresponded to common English words such as “the,” “this,” and “have,” and that these mappings held consistently across the text. Fourth, a stylistic reconstruction test was applied to evaluate whether the decryption produced naturally flowing, idiomatic language typical of the period—an outcome highly unlikely to occur by random or incorrect mappings. Finally, all remaining unmapped codes were reviewed to confirm that they occurred in non-essential or supplemental positions, such as endings or transitions, posing no threat to the core semantic fidelity. Collectively, these verification layers provide a high-confidence confirmation of the decrypted message’s authenticity and accuracy.

Reference Letters from John Armstrong to James Madison:

• To James Madison from John Armstrong, 15 July 1804. Discusses diplomatic tensions, neutrality, and maritime affairs.
• To James Madison from John Armstrong, 7 June 1806.  Covers French relations and commercial restrictions relevant to U.S. interests.

Armstrong–Madison Cipher Codebook:

Entry #	Code	Word
1	1	our
2	6	i
3	12	rights
4	13	ministry
5	14	this
6	17	of
7	18	the
8	27	french
9	28	shipping
10	36	deeply
11	38	and
12	39	written
13	44	and
14	45	have
15	48	relation
16	65	has
17	67	enter
18	76	their
19	88	that
20	98	treatment
21	121	government
22	131	to
23	143	before
24	240	to
25	246	no
26	356	has
27	370	to
28	381	given
29	384	you
30	387	must
31	388	have
32	432	its
33	436	on
34	454	declared
35	489	this
36	496	which
37	564	commerce
38	640	ports
39	671	in
40	681	petitions
41	751	neutral
42	946	subject
43	1120	assurance
44	1170	nor
45	1180	concerning
46	1254	been
47	1267	have
48	1320	commerce
49	1340	your
50	1358	that
51	1540	shipping
52	1640	american
53	1760	ships
54	1761	the
55	1842	satisfaction
56	1900	affects