David Stein, "The Puzzle at CIA Headquarters: Cracking the Courtyard Crypto" (Studies in…

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.

David D. Stein, Central Intelligence Agency, 1999. Public domain

Copies 1

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's published

Where it was made

Courtyard of CIA headquarters, Langley · Building courtyard

Sources 1

The Puzzle at CIA Headquarters: Cracking the Courtyard CryptoSRC

Cite it

Mysteries Department. (2026). David Stein, "The Puzzle at CIA Headquarters: Cracking the Courtyard Crypto" (Studies in… [Copy CPY0D7HTKH41PMZ]. https://mysteriesdept.com/r/CPY0D7HTKH41PMZ

@misc{mysteriesdept_art0d7htjsp0mda,
  title     = {David Stein, "The Puzzle at CIA Headquarters: Cracking the Courtyard Crypto" (Studies in…},
  author    = {{Mysteries Department}},
  year      = {2026},
  note      = {Artifact, catalog key CPY0D7HTKH41PMZ},
  url       = {https://mysteriesdept.com/r/CPY0D7HTKH41PMZ}
}