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Sanitization of FHE Ciphertexts
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Additionally, when a public key is provided, ciphertexts are also re-randomizable, e.g., by adding to them fresh encryptions of 0. From those two operations we devise an algorithm to sanitize a ciphertext, by making its distribution canonical. In particular, the distribution of the ciphertext does not depend on the circuit that led to it via homomorphic evaluation, thus providing circuit privacy in the honest-but-curious model. Unlike the previous approach based on noise flooding, our approach does not degrade much the security/efficiency trade-off of the underlying FHE. The technique can be applied to all lattice-based FHE proposed so far, without substantially affecting their concrete parameters." /> <meta property="article:section" content="PUBLICKEY" /> <meta property="article:modified_time" content="2025-03-17T10:05:38+00:00" /> <meta property="article:published_time" content="2016-02-19T20:16:36+00:00" /> </head> <body> <noscript> <h1 class="text-center">What a lovely hat</h1> <h4 class="text-center">Is it made out of <a href="https://iacr.org/tinfoil.html">tin foil</a>?</h4> </noscript> <div class="fixed-top" id="topNavbar"> <nav class="navbar navbar-custom navbar-expand-lg"> <div class="container px-0 justify-content-between justify-content-lg-evenly"> <div class="order-0 align-items-center d-flex"> <button class="navbar-toggler btnNoOutline" type="button" data-bs-toggle="collapse" data-bs-target="#navbarContent" aria-controls="navbarContent" aria-expanded="false"> <span class="icon-bar top-bar"></span> <span class="icon-bar middle-bar"></span> 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Homomorphic Encryption (SHE) scheme via this technique. Additionally, when a public key is provided, ciphertexts are also re-randomizable, e.g., by adding to them fresh encryptions of 0. From those two operations we devise an algorithm to sanitize a ciphertext, by making its distribution canonical. In particular, the distribution of the ciphertext does not depend on the circuit that led to it via homomorphic evaluation, thus providing circuit privacy in the honest-but-curious model. Unlike the previous approach based on noise flooding, our approach does not degrade much the security/efficiency trade-off of the underlying FHE. The technique can be applied to all lattice-based FHE proposed so far, without substantially affecting their concrete parameters.</p> <p><strong>Note:</strong> As pointed out in [SW25/eprint 2025/275], the sanitization definition is incorrect. It should only require correct bootstrapping for honestly generated ciphertexts. The strong definition is neither achieved by the sanitization algorithm, nor required for the application (honest-but curious circuit privacy). The weakened definition is achieved by the algorithm and suffices for the application.</p> </div> <div id="metadata" class="col-md-5 col-lg-4 ps-md-5 mt-4 mt-md-0"> <h5>Metadata</h5> <dl> <dt> Available format(s) </dt> <dd> <a class="btn btn-sm btn-outline-dark" href="/2016/164.pdf"> <img class="icon" src="/img/file-pdf.svg">PDF</a> </dd> <dt>Category</dt> <dd><a href="/search?category=PUBLICKEY"><small class="badge category category-PUBLICKEY">Public-key cryptography</small></a></dd> <dt>Publication info</dt> <dd>Published by the IACR in EUROCRYPT 2016</dd> <dt>Contact author(s)</dt> <dd><span class="font-monospace"> damien stehle<span class="obfuscate"> @ </span>gmail com </span> </dd> <dt>History</dt> <dd>2025-03-17: revised</dd> <dd>2016-02-19: received</dd> <dd><a rel="nofollow" href="/archive/versions/2016/164">See all versions</a></dd> <dt>Short URL</dt> <dd><a href="https://ia.cr/2016/164">https://ia.cr/2016/164</a></dd> <dt>License</dt> <dd><a rel="license" target="_blank" href="https://creativecommons.org/licenses/by/4.0/"> <img class="licenseImg" src="/img/license/CC_BY.svg" alt="Creative Commons Attribution" title="Creative Commons Attribution"><br> <small>CC BY</small> </a> </dd> </dl> </div> </div> <p class="mt-4"><strong>BibTeX</strong> <button id="bibcopy" class="ms-2 btn btn-sm btn-outline-dark" aria-label="Copy to clipboard" onclick="copyBibtex()"> <img src="/img/copy-outline.svg" class="icon">Copy to clipboard</button></p> <pre id="bibtex"> @misc{cryptoeprint:2016/164, author = {Léo Ducas and Damien Stehlé}, title = {Sanitization of {FHE} Ciphertexts}, howpublished = {Cryptology {ePrint} Archive, Paper 2016/164}, year = {2016}, url = {https://eprint.iacr.org/2016/164} } </pre> <script> var bibcopy; function triggerTooltip() { console.log('setting tooltip'); } window.onload = triggerTooltip; function copyBibtex() { let range = document.createRange(); range.selectNode(document.getElementById('bibtex')); window.getSelection().removeAllRanges(); window.getSelection().addRange(range); document.execCommand('copy'); window.getSelection().removeAllRanges(); let bibcopy = document.getElementById('bibcopy'); let copyTooltip = new bootstrap.Tooltip(bibcopy, {trigger: 'manual', title: 'Copied!'}); copyTooltip.show(); setTimeout(function() { copyTooltip.dispose(); }, 2000); } </script> </main> <div class="container-fluid mt-auto" id="eprintFooter"> <a href="https://iacr.org/"> <img id="iacrlogo" src="/img/iacrlogo_small.png" class="img-fluid d-block mx-auto" alt="IACR Logo"> </a> <div class="colorDiv"></div> <div class="alert alert-success w-75 mx-auto"> Note: In order to protect the privacy of readers, eprint.iacr.org does not use cookies or embedded third party content. </div> </div> <script src="/css/bootstrap/js/bootstrap.bundle.min.js"></script> <script> var topNavbar = document.getElementById('topNavbar'); if (topNavbar) { document.addEventListener('scroll', function(e) { if (window.scrollY > 100) { topNavbar.classList.add('scrolled'); } else { topNavbar.classList.remove('scrolled'); } }) } </script> </body> </html>