NSA releases 52,000 pages of William F. Friedman Collection,
   searchable:
   [1]https://www.nsa.gov/public_info/declass/friedman_documents/index.sht
   ml
   Document index spreadsheet:
   [2]https://www.nsa.gov/public_info/_files/friedmanDocuments/Friedman_Co
   llection_Metadata.xlsx

References

   1. https://www.nsa.gov/public_info/declass/friedman_documents/index.shtml
   2. https://www.nsa.gov/public_info/_files/friedmanDocuments/Friedman_Collection_Metadata.xlsx