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

Fig. 1b. Decryption Strategies for Receiving Secure Documents: Multiple keys on a ring are Public keys (Ann, certifying organization, time/date stamping organization), while the individual key represents a Private Key (Bob). The sequence involved is (A) Bob decrypts the Session Key using his Private Key. (B) This symmetric key is used to decrypt the received document. (C) The Public Keys of the third-parties providing Certification and Time/Date assurance are used to decrypt their slips. (D) Ann's Public Key is used to recover the Message Digest. (E) Bob hashes the decrypted document and compares his version of the Message Digest with the transmitted version. If the two are identical, and the Certification, and Time/Date Slips decrypt properly, then Bob can have assurance in the deciphered document.