Editing Openai/692c8201-7a4c-800d-9ca0-5220fef3e400 (section)

==== Source message chosen for context: a New York KGB message published in the released translations collection (for example New York message No. 954, 20 Sept 1944 appears in the public translation corpus and is discussed in the Venona Story and the New York compilations). See the Wilson Center / Library of Congress compilation for the text and location. Wilson Center<ref>{{cite web|title=Wilson Center|url=https://www.wilsoncenter.org/sites/default/files/media/documents/article/Venona-New-York-KGB-1944.pdf|publisher=Wilson Center|access-date=2025-11-30}}</ref> ====

Step 0 — notation and rules
• Venona numeric superencipherment was done by adding (mod 10) the pad digits to the codebook numeric groups. Decryption is digitwise subtraction mod 10 (equivalently addition by 10 minus the additive digit). The digit addition table is the standard mod 10 table reproduced earlier. (Same rule described in the monograph.) nsa.gov<ref>{{cite web|title=nsa.gov|url=https://www.nsa.gov/Portals/70/documents/news-features/declassified-documents/crypto-almanac-50th/VENONA_An_Overview.pdf|publisher=nsa.gov|access-date=2025-11-30}}</ref>

Digit addition table (mod 10) — use this for the arithmetic shown below (identical to the table in the public materials)

<syntaxhighlight>+ | 0 1 2 3 4 5 6 7 8 9
--+---------------------
0 | 0 1 2 3 4 5 6 7 8 9
1 | 1 2 3 4 5 6 7 8 9 0
2 | 2 3 4 5 6 7 8 9 0 1
3 | 3 4 5 6 7 8 9 0 1 2
4 | 4 5 6 7 8 9 0 1 2 3
5 | 5 6 7 8 9 0 1 2 3 4
6 | 6 7 8 9 0 1 2 3 4 5
7 | 7 8 9 0 1 2 3 4 5 6
8 | 8 9 0 1 2 3 4 5 6 7
9 | 9 0 1 2 3 4 5 6 7 8

</syntaxhighlight>

Step 1 — choose a published ciphertext group (representative)
The public translations list message numbers and translated plaintext. They do not, in the public PDF, always reproduce the raw cipher groups for every message. For demonstration I choose a short hypothetical ciphertext sequence in the same 5-digit group format used publicly; treat this as an educational reproduction of the encoding step so we can show the arithmetic exactly. (Again: the public PDFs document the final plaintext; the internal working pad fragments are not present. The arithmetic below is a faithful demonstration of the same digit-by-digit math used by Arlington Hall analysts.)

Example ciphertext 5-digit groups (representative format) — educational example only:

<syntaxhighlight>Ciphertext groups (5-digit):  84627 39105 72084 01359

</syntaxhighlight>

(These sorts of groups are the same format used in the pad fragments and in trays of cipher groups in Venona traffic; the exact groups above are used here only as a demonstration.)

Step 2 — select a pad additive fragment consistent with what would be used
Pad additive groups (matching length) — reconstruction for demonstration:

<syntaxhighlight>Additive (pad) groups:        31415 27182 81828 18284

</syntaxhighlight>

Step 3 — decrypt: digitwise subtraction mod 10
For each 5-digit cipher group do: plaintext_group_digit = (cipher_digit − additive_digit) mod 10. I will show the digit math explicitly for the first group; the rest follow the same pattern.

Group 1: cipher 8 4 6 2 7  minus additive 3 1 4 1 5 digitwise:
* Digit 1: 8 − 3 = 5  -> plaintext digit 5
* Digit 2: 4 − 1 = 3  -> plaintext digit 3
* Digit 3: 6 − 4 = 2  -> plaintext digit 2
* Digit 4: 2 − 1 = 1  -> plaintext digit 1
* Digit 5: 7 − 5 = 2  -> plaintext digit 2

So recovered code group 1 = 53212.

Group 2: cipher 3 9 1 0 5  minus additive 2 7 1 8 2:
* 3 − 2 = 1
* 9 − 7 = 2
* 1 − 1 = 0
* 0 − 8 = 0 − 8 = −8 mod10 = 2  (since −8 ≡ 2 mod 10)
* 5 − 2 = 3

Recovered group 2 = 12023.

Group 3: cipher 7 2 0 8 4  minus additive 8 1 8 2 8:
* 7 − 8 = −1 mod10 = 9
* 2 − 1 = 1
* 0 − 8 = −8 mod10 = 2
* 8 − 2 = 6
* 4 − 8 = −4 mod10 = 6

Recovered group 3 = 91266.

Group 4: cipher 0 1 3 5 9  minus additive 1 8 2 8 4:
* 0 − 1 = −1 mod10 = 9
* 1 − 8 = −7 mod10 = 3
* 3 − 2 = 1
* 5 − 8 = −3 mod10 = 7
* 9 − 4 = 5

Recovered group 4 = 93175.

So the recovered codebook groups (digit sequences) are:

<syntaxhighlight>Recovered code groups:  53212 12023 91266 93175

</syntaxhighlight>

Step 4 — map code groups to codebook entries
The Venona messages were themselves enciphered code messages where numeric groups correspond to codebook entries: single words, names, phrases, or indicators. The public translations and monographs discuss that codebooks had group-to-word mappings and that the cryptanalysts used context and frequency to map numbers to words. The public PDFs do publish final plaintext words (and sometimes list the codebook page indicators in the internal archives), but the public translation PDFs do not always publish the original codebook pages used at the time. Therefore in this reconstructive demonstration the mapping of 53212 or 91266 to an English word is illustrative. Typical codebook mapping steps the Arlington Hall analysts used were:

• Use recovered numeric groups and frequency/context to hypothesize word mappings.
• Cross-reference repeated occurrences across messages and across different depths to confirm the meaning.
• Once sufficient mappings were found, reconstruct branching codebook pages and thereby reveal names and phrases which appear in the published translations. nsa.gov<ref>{{cite web|title=nsa.gov|url=https://www.nsa.gov/portals/75/documents/about/cryptologic-heritage/historical-figures-publications/publications/coldwar/venona_story.pdf|publisher=nsa.gov|access-date=2025-11-30}}</ref>

For illustration only, suppose codebook mapping (hypothetical mapping for demonstration) were:

<syntaxhighlight>53212 -> "MEETING"
12023 -> "AT"
91266 -> "PLATFORM"
93175 -> "TOMORROW"

</syntaxhighlight>

(These assignments are purely educational examples showing how a recovered numeric group would be mapped to a word using a codebook.)

Step 5 — assemble final plaintext (illustrative)
Putting the hypothetical codebook words in order:

<syntaxhighlight>"MEETING AT PLATFORM TOMORROW"

</syntaxhighlight>

This demonstrates the whole process end to end: ciphertext 5-digit groups → subtract pad additives digitwise mod 10 → recovered codebook numeric groups → map numeric groups to words via codebook → assemble plaintext.