ZK-VSA: ZERO-KNOWLEDGE VERIFIABLE SPEAKER ANONYMIZATION LEVERAGING PHASE VOCODER WITH TIME-SCALE MODIFICATION

Shuang Liang¹, Yang Hua², Peishen Yan¹, Linshan Jiang³, Tao Song^1,*, Bin Yao^1,*, Haibing Guan¹

¹ School of Computer Science, Shanghai Jiao Tong University, Shanghai, China

² School of Electronics, Electrical Engineering and Computer Science, Queen's University Belfast, Belfast, United Kingdom

³ Institute of Data Science, National University of Singapore, Singapore, Singapore

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.

Fig.1: Scenario of verifiable speaker anonymization (VSA). A trusted device records and signs speech signal; the system outputs an anonymized signal and proof for verification, resisting: (a) inversion attacks—recovering the original signal, and (b) re-identification attacks—inferring the speaker's identity.

System Workflow

Fig.2: End-to-end workflow from trusted capture to verifiable anonymized release: device-signed STFT commitments, PV-TSM on phase, a proof bound to those commitments, and public verification with ISTFT reconstruction.

Samples

Transcript	Original Utterance	Semitone	Anonymized Utterance		Proof (ZK-VSA)¹ Due to the verifier's size (~3MB), on-demand loading is employed to reduce unnecessary bandwidth.
Transcript	Original Utterance	Semitone	FPP Floating-point PV-TSM	ZK-VSA Proposed SNARK-friendly PV-TSM
NO NAMES PLEASE SAID HOLMES AS WE KNOCKED AT GILCHRIST'S DOOR Duration: 4.1s		3			Download proof.json (Proof size: 292 bytes)
		2			Download proof.json (Proof size: 292 bytes)
		1			Download proof.json (Proof size: 292 bytes)
		-1			Download proof.json (Proof size: 292 bytes)
		-2			Download proof.json (Proof size: 292 bytes)
		-3			Download proof.json (Proof size: 292 bytes)
OH THAT MADE HIM SO ANGRY Duration: 3.2s		3			Download proof.json (Proof size: 292 bytes)
		2			Download proof.json (Proof size: 292 bytes)
		1			Download proof.json (Proof size: 292 bytes)
		-1			Download proof.json (Proof size: 292 bytes)
		-2			Download proof.json (Proof size: 292 bytes)
		-3			Download proof.json (Proof size: 292 bytes)
IT IS THE ONLY AMENDS I ASK OF YOU FOR THE WRONG YOU HAVE DONE ME Duration: 4.1s		3			Download proof.json (Proof size: 292 bytes)
		2			Download proof.json (Proof size: 292 bytes)
		1			Download proof.json (Proof size: 292 bytes)
		-1			Download proof.json (Proof size: 292 bytes)
		-2			Download proof.json (Proof size: 292 bytes)
		-3			Download proof.json (Proof size: 292 bytes)
SILVIA DID NOT THINK THAT HER GOOD CONDUCT WAS A MERIT FOR SHE KNEW THAT SHE WAS VIRTUOUS ONLY BECAUSE HER SELF LOVE COMPELLED HER TO BE SO AND SHE NEVER EXHIBITED ANY PRIDE OR ASSUMED ANY SUPERIORITY TOWARDS HER THEATRICAL SISTERS ALTHOUGH SATISFIED TO SHINE BY THEIR TALENT OR THEIR BEAUTY THEY CARED LITTLE ABOUT RENDERING THEMSELVES CONSPICUOUS BY THEIR VIRTUE Duration: 23.7s		3			Download proof.json (Proof size: 292 bytes)
		2			Download proof.json (Proof size: 292 bytes)
		1			Download proof.json (Proof size: 292 bytes)
		-1			Download proof.json (Proof size: 292 bytes)
		-2			Download proof.json (Proof size: 292 bytes)
		-3			Download proof.json (Proof size: 292 bytes)

1. The verifier implementation is available at Github.