SECRET KEY DELIVERING SYSTEM

PURPOSE:To attain key delivery without decreasing the through-put of data communication by constituting the system that the key is delivered once only at acquisition of a line. CONSTITUTION:When a communication request comes from a data terminal device DTE1, a network controller NCU4 is started and a call to a public network is conducted. When an exchange sets a line with an opposite network controller NCU5, the NCU4 informs it to a line terminator DCE3. The DCE3 sets a data set ready signal DR to a ciphering device DEE2. When the ciphering device DEE2 receives the DR signal from the DCE3, the DEE2 sets the DR signal to the DTE1 so as to allow the DTE1 to output a transmission request signal RS. When the DCE3 receives an RS signal, a ciphering device DEE7 of the opposite station receives it and transmits a ready signal RR. Thus, the ciphering device DEE2 delivers a secret key with the opposite DEE7.