ZK-VSA: Zero-Knowledge Verifiable Speaker Anonymization Leveraging Phase Vocoder with Time-Scale Modification

Abstract

Speaker anonymization protects against speaker identity inference, yet third parties cannot verify that released speech is authenticated and anonymized as predefined without revealing the original. We propose Verifiable Speaker Anonymization (VSA), a paradigm that enables public verification that a predefined anonymization has been applied while the original remains hidden. We instantiate this paradigm as ZK-VSA using zero-knowledge succinct non-interactive arguments of knowledge (ZK-SNARKs): we encode phase vocoder with time-scale modification (PV-TSM) as arithmetic constraints suitable for succinct proofs, complemented by SNARK-friendly phase handling, and integrate cryptographic commitments with digital signatures for authentication. We evaluate ZK-VSA on LibriSpeech, using automatic speech recognition (ASR) for intelligibility and automatic speaker verification (ASV) for anonymity. Our proof-constrained anonymization closely matches floating-point PV-TSM, while proofs add only a slight overhead and verify in milliseconds. These results demonstrate the practicality of VSA and open a path to proof-based guarantees for broader speech transformations.