Plausible Deniability in Fully Homomorphic Computation
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arXiv
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| Format: | Preprint |
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2026
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| _version_ | 1866917456855957504 |
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| author | Ahmad, Shahzad Rass, Stefan Seyedi, Zahra |
| author_facet | Ahmad, Shahzad Rass, Stefan Seyedi, Zahra |
| contents | We introduce \emph{Plausible Deniability in Fully Homomorphic Computation} (PD-FHC), a framework enabling users to outsource Boolean computations to an untrusted cloud while maintaining both computational privacy against honest-but-curious providers and plausible deniability against coercive adversaries. We define the notion of a \emph{Deniable Computation Medium} (DCM) and a \emph{Deniable Computation Scheme} (DCS) as medium-independent abstractions, then instantiate them using RGB images with Fredkin-gate circuits. Multiple computation scenarios (one real, several decoys) are embedded at secret positions within cover images; the cloud applies identical operations to every pixel, processing all scenarios uniformly. Under coercion, the user reveals a decoy computation with verifiable results while the real computation remains hidden. We formalize multi-round coercion games with existence and intent distinguishing advantages, proving computational privacy with advantage $Θ(1/(n-1)!)$ and negligible existence-hiding advantage for the image instantiation. Our Python implementation, benchmarked across circuit sizes (5--289 gates) and image dimensions ($128^2$ to $512^2$), demonstrates competitive performance with TFHE for Boolean circuits while providing deniability that FHE fundamentally cannot offer. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2605_01985 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Plausible Deniability in Fully Homomorphic Computation Ahmad, Shahzad Rass, Stefan Seyedi, Zahra Cryptography and Security We introduce \emph{Plausible Deniability in Fully Homomorphic Computation} (PD-FHC), a framework enabling users to outsource Boolean computations to an untrusted cloud while maintaining both computational privacy against honest-but-curious providers and plausible deniability against coercive adversaries. We define the notion of a \emph{Deniable Computation Medium} (DCM) and a \emph{Deniable Computation Scheme} (DCS) as medium-independent abstractions, then instantiate them using RGB images with Fredkin-gate circuits. Multiple computation scenarios (one real, several decoys) are embedded at secret positions within cover images; the cloud applies identical operations to every pixel, processing all scenarios uniformly. Under coercion, the user reveals a decoy computation with verifiable results while the real computation remains hidden. We formalize multi-round coercion games with existence and intent distinguishing advantages, proving computational privacy with advantage $Θ(1/(n-1)!)$ and negligible existence-hiding advantage for the image instantiation. Our Python implementation, benchmarked across circuit sizes (5--289 gates) and image dimensions ($128^2$ to $512^2$), demonstrates competitive performance with TFHE for Boolean circuits while providing deniability that FHE fundamentally cannot offer. |
| title | Plausible Deniability in Fully Homomorphic Computation |
| topic | Cryptography and Security |
| url | https://arxiv.org/abs/2605.01985 |