Phonotactic Reconstruction of Encrypted VoIP Conversations: Hookt on fon-iks
In this paper, the authors unveil new privacy threats against Voice-over-IP (VoIP) communications. Although prior work has shown that the interaction of variable bit-rate codecs and length-preserving stream ciphers leaks information, they show that the threat is more serious than previously thought. In particular, they derive approximate transcripts of encrypted VoIP conversations by segmenting an observed packet stream into subsequences representing individual phonemes and classifying those subsequences by the phonemes they encode. Drawing on insights from the computational linguistics and speech recognition communities, they apply novel techniques for unmasking parts of the conversation.