schriste@uceng.UC.EDU (Steven V. Christensen) (11/29/90)
Hi, Last month (I think) I saw a project in one of the Radio Electronic type magazines about a self conrained telephone line controller. Basically it hooked in parallel with all your phones, and could be made to prevent numbers beginning with certain prefixes from being dialed. Does anyone know how this is done, since the device is in parallel with all other phones? How can it prevent me from completing calls beginning with "1900..."? Thanks, Steven -- Steven V. Christensen U.C. College of Eng. schriste@uceng.uc.edu For the adventurous: svc@elf0.uucp
ropg@ooc.uva.nl (Rop Gonggrijp) (12/03/90)
schriste@uceng.UC.EDU (Steven V. Christensen) writes: > Last month (I think) I saw a project in one of the Radio >Electronic type magazines about a self conrained telephone line >controller. Basically it hooked in parallel with all your phones, and >could be made to prevent numbers beginning with certain prefixes from >being dialed. > Does anyone know how this is done, since the device is in >parallel with all other phones? How can it prevent me from completing >calls beginning with "1900..."? A device that does this needs at least a way of detecting dial pulses (peaks in line voltage if hooked up in parallel. How would a device that is hooked up in parallel break the connection though? It cannot hang up, it can only short the wires so that there is no audio. Needless to say this can still mean very high phone bills. In this simplest version DTMF-dialling would also defeat it. Even if it had a DTMF-decoder fitted, you could still fool it by blowing either: -so low that the phone switch hears it but the device doesn't (at least the first few digits or, if the device is more sensitive than the switch (which is more likely) -so low that the device does hear you, but the switch still provides a dial- tone. Then dial a few innocent (local) digits and then tell the CO to call Mars..... Conclusion: the only hack-proof way of doing this is by using a device that detects dialling on one end and repeats it to the CO. This way there is the absolute certainty no digits are slipped in-between. All other ways lead to fraud if exposed to the general public (this does NOT mean, the 'safer' method is hack-proof in every implementation (see COCOTS)). -- Rop Gonggrijp (ropg@ooc.uva.nl) is also editor of Hack-Tic (hack/phreak mag.) quote: "We don't care about freedom of the mind, | Postbus 22953 (in DUTCH) freedom of signature will do just fine" | 1100 DL AMSTERDAM Any opinions in this posting are wasted on you | tel: +31 20 6001480
dclaar@hpcuhc.cup.hp.com (Doug Claar) (12/11/90)
The phones hook up to the device, and the device to the line. The device generates ringing voltage, etc for the phones. Given this implementation, it is (I think) obvious how it works, and how to bypass it: Physically. Doug Claar HP Computer Systems Division UUCP: mcvax!decvax!hplabs!hpda!dclaar -or- ucbvax!hpda!dclaar ARPA: dclaar%hpda@hplabs.HP.COM