Let's assume we have a computer that sends packets to the internet using dial-up connection, and we have access to the analog data on the phone line(we have access to the phone line), how can we make a proper sniff for the data that is being transmitted through?


1 Answer 1


If it is a PSTN line a simple tape recorder attached to the lines could do the trick. For ISDN I suspect you need a DAC but its also easy, as long as you have physical access to the line.

Any connection using a Telephone line (digital or analogue) is easy to understand for anyone that knows the encoding schema. To realy protect it you should use the same techniques as being used between computers. There we ue an encription layer in between the physical line and the interpretation layer (a.k.a. between the telephone receiver and the physical telephone line) The current default implementation for this is the TLS Protocol, this encrypts everything but the name of the intended 'destination' (so phone number and name)

Bottom Line, if you want to protect your physical line use a TLS connection.

  • Could this way lead to a "data sniffing", and to get the plain http requests, for example? May 22, 2015 at 14:32
  • Yes, you can see everything going over the line!
    – LvB
    May 22, 2015 at 14:33
  • And one more question! Is the DAC enough to take care of it? May 22, 2015 at 14:34
  • the Digital Analogue Converter is to record a Digital Signal on a Analogue Medium. So its just there to be able to store a digital signal on a tape. if you use digital recording technology you probably already have that. (its the same thing that is done to speech when you use a cell-phone)
    – LvB
    May 22, 2015 at 14:36

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