Compressed web phone calls are easy to bug

Compressed web phone calls are easy to bug
Compressed web phone calls are easy to bug 

By David Robson news service
12 June 2008

Plans to compress internet (VoIP) phone calls so they use less bandwidth 
could make them vulnerable to eavesdropping. Most networks are currently 
safe, but many service providers are due to implement the flawed 
compression technology.

The new compression technique, called variable bitrate compression 
produces different size packets of data for different sounds.

That happens because the sampling rate is kept high for long complex 
sounds like "ow", but cut down for simple consonants like "c". This 
variable method saves on bandwidth, while maintaining sound quality.

VoIP streams are encrypted to prevent eavesdropping. However, a team 
from John Hopkins University in Baltimore, Maryland, US, has shown that 
simply measuring the size of packets without decoding them can identify 
whole words and phrases with a high rate of accuracy.


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