The worldwide dial plan proposed by the International Telecommunication Union recommendation E.164 reserves multiple country codes for future use. These unused codes present an opportunity for a potential covert channel over the public switched telephone network utilizing a spoofed source phone number of a call to send information to a mobile device. The reserved country codes can act as a delimiter indicating that a secret message is being sent. By spooï¬ng a call using a reserved country code number, the application listening on the mobile device will be able to intercept the call and extract information from the remaining digits based on ASCII encoding in a decimal format. The purpose of using a reserved country code number is so that there will be no denied service to the user with a call from a legitimate phone number.
Date of creation, presentation, or exhibit
Department, Program, or Center
Department of Computing Security (GCCIS)
Harmat, Bryan; Stroud, Jared; and Johnson, Daryl, "A Covert Channel in the Worldwide Public Switched Telephone Network Dial Plan" (2015). Accessed from
RIT – Main Campus