Analysis of encrypted VoIP traffic by packet size

    Successfully listen to conversations over VoIP possible even if the VoIP-traffic is securely encrypted. The fact is that modern sound encryption algorithms are specially optimized for voice coding with maximum quality with a narrow bandwidth. Therefore, some services use VBR compression. The acronym VBR stands for “variable bitrate,” that is, a change in bit rate depending on the content of the content. This “advanced” technology has not yet received wide distribution, but many VoIP services plan to implement it in the future.

    When using VBR, long complex sounds (op) are encoded with a high bit rate, and small simple sounds (t) are encoded with a small bitrate to save bandwidth. So, scientists have found a way to restore the original content by analyzing the bitrate and linguistic analysis using a database of phonemes and words.

    Specialists from Johns Hopkins University have shown that a simple analysis of packet sizes already provides enough information to restore the original words and phrases. These can be passwords and other sensitive information.

    Phrase recognition accuracy is 50%, and long complex words - 90%.

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