Intercepting and instrumenting COM applications
COOTS'99 Proceedings of the 5th conference on USENIX Conference on Object-Oriented Technologies & Systems - Volume 5
Detours: binary interception of Win32 functions
WINSYM'99 Proceedings of the 3rd conference on USENIX Windows NT Symposium - Volume 3
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Phone based card payments utilize inband DTMF signaling to convey data. Since the DTMF signals are audible to a human ear, a call operator is in position to carry out a privacy attack. We investigate real-time techniques that can obfuscate the 'digit' values without deteriorating the voice quality. Furthermore, we consider a setting where the privacy solution is being provided by a third party which does not have the benefit of open interfaces to the communication application. Our experiments reveal the efficacy of binary interception to 'inject' the signal filtering. Meanwhile, we observe that several DTMF suppression techniques that have been proposed in literature can leave a residue that is sufficient for de-anonymizing the digit value. In light of these observations, we argue in favor of more modest privacy guarantees, which can be achieved by suppressing only the higher frequency. We show that margin crossings and peak variances can be used for fast pre-filtering of audio to detect the presence of a tone, thus reducing the computational needs.