In this illustration we see Alice looking rightwards. Above her is the message, m, and below her is the symmetric session key, KS. A blue arrow points from the message to a white box labeled KS(.). The blue arrow, now labeled KS(m), extends rightward from the box, then vertically downward to a circle labeled "+." A blue arrow extends from the symmetric session key to a white box labeled K (+/B) ( . ). The blue arrow, now labeled K B+ ( K S ) extends rightward from the box, then vertically upwards to the circle labeled "+." A blue arrow points rightward from the circle to a cloud representing the Internet. This entire process is labeled "Alice sends e-mail message m."

A blue arrow extends rightward from the Internet to a circle labeled "-." An arrow extends upwards from the circle and then horizontally rightward, now labeled KS(m), to a white box labeled KS(.). A blue arrow extends downward from the circle and then horizontally rightward, now labeled K B+ (KS ), to a white box labeled K B- ( . ). A blue arrow, labeled KS, extends vertically upwards from this box to the box labeled KS(.). A blue arrow extends rightward from this box, delivering the message, m, to Bob. This entire process is labeled "Bob receives e-mail message m."