Files W.F.F. Archive Patent and Equipment Records Correspondence, Description, Diagrams, SISDE-20, Cipher System and Apparatus for Plural-Unit-Code Telegraph Printer, 1936-1939
Cryptographic and Operating Advantages for Proposed Machine, 1 January 1944; SISDE 20
Department of State Cover Letter Enclosing an IBM Proposal for A Cryptographic System; SISDE 20
Friedman Invention; Cipher System for Teletype and Radiotype (SISDE-20), 11 January 1944
Invention of A Cipher System and Apparatus for Plural-Unit-Code Telegraph Printer, 14 June 1936; SISDE 20