Fig. 1a, from The code makers, by Raymond E. Dessy, Trends in Analytical Chemistry, 16 (1997) 1. © 1996 Elsevier Science bv.

Fig. 1a. Encryption Strategies for Sending Secure Documents: Single keys are Private Keys (Ann, certifying organization, time/date stamping organization), while multiple keys on a ring are Public Keys (Bob). The sequence involved is (A) Ann hashes the document to a Message Digest (PostIt Note), and then creates a Digital Signature using her Private Key. (B) This is placed in an encryptolope, along with Certificate slip(s) and Time/Date stamps from third-parties verifying Ann's identity and the time of creation. (C) A symmetric Session Key is created. (D) The document is encrypted with the key. (E) The Session Key is encrypted with Bob's Public Key and attached to the ciphered document. The encryptolope, encrypted document, and associated encrypted key are sent as a unit.