The CIA analyst's own account of solving K1 to K3 by hand over about 400 hours from 1991 to 1998, with the plaintexts; written for the agency's internal journal and later declassified.
Central Intelligence Agency (declassified release), 1999. Public domain
Copies 2
ScanCentral Intelligence Agency (declassified release) · nsarchive2.gwu.edu · Public domain (US government work)Primary source: The Puzzle at CIA Headquarters: Cracking the Courtyard Crypto1 step from the original
Cracking the courtyard crypto" (studies in…David D. Stein, Central Intelligence Agency · nsarchive2.gwu.edu · Public domain (US government work)1 step from the original
Where it was made
Courtyard of CIA headquarters, Langley · Building courtyard
Sources 1
Cite it
Mysteries Department. (2026). David Stein, "The Puzzle at CIA Headquarters: Cracking the Courtyard Crypto" (Studies in Intelligence, 1999) [Artifact ART0D7HTJSP0MDA]. https://mysteriesdept.com/r/ART0D7HTJSP0MDA
@misc{mysteriesdept_art0d7htjsp0mda,
title = {David Stein, "The Puzzle at CIA Headquarters: Cracking the Courtyard Crypto" (Studies in Intelligence, 1999)},
author = {{Mysteries Department}},
year = {2026},
note = {Artifact, catalog key ART0D7HTJSP0MDA},
url = {https://mysteriesdept.com/r/ART0D7HTJSP0MDA}
}