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Breaking the Shadow: Key Recovery Attack on Full-Round Shadow Block Ciphers with Minimal Data
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Both variants use a generalized Feistel network with four branches, incorporating the AND-Rotation-XOR operation similar to the Simon family for their bridging function. This paper reveals that the security claims of the Shadow family are not as strong as suggested. We present a key recovery attack that can retrieve the sequence of round keys used for encryption with only two known plaintext/ciphertext pairs, requiring time and memory complexity of $2^{43.23}$ encryptions and $2^{21.62}$ blocks of memory for Shadow-32, and complexity of $2^{81.32}$ encryptions and $2^{40.66}$ blocks of memory for Shadow-64. Notably, this attack is independent of the number of rounds and the bridging function employed. Furthermore, we critically evaluate one of the recent cryptanalysis on Shadow ciphers and identify significant flaws in the proposed key recovery attacks. In particular, we demonstrate that the distinguisher used in impossible differential attacks by Liu et al. is ineffective for key recovery, despite their higher claimed complexities compared to ours." /> <meta property="article:section" content="SECRETKEY" /> <meta property="article:modified_time" content="2025-03-23T19:51:13+00:00" /> <meta property="article:published_time" content="2024-12-29T15:49:20+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 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Rasoolzadeh</span><span class="affiliation">, Ruhr University Bochum, Bochum, Germany</span></div> <h5 class="mt-3">Abstract</h5> <p style="white-space: pre-wrap;">Shadow is a family of lightweight block ciphers introduced by Guo, Li, and Liu in 2021, with Shadow-32 having a 32-bit block size and a 64-bit key, and Shadow-64 having a 64-bit block size and a 128-bit key. Both variants use a generalized Feistel network with four branches, incorporating the AND-Rotation-XOR operation similar to the Simon family for their bridging function. This paper reveals that the security claims of the Shadow family are not as strong as suggested. We present a key recovery attack that can retrieve the sequence of round keys used for encryption with only two known plaintext/ciphertext pairs, requiring time and memory complexity of $2^{43.23}$ encryptions and $2^{21.62}$ blocks of memory for Shadow-32, and complexity of $2^{81.32}$ encryptions and $2^{40.66}$ blocks of memory for Shadow-64. Notably, this attack is independent of the number of rounds and the bridging function employed. Furthermore, we critically evaluate one of the recent cryptanalysis on Shadow ciphers and identify significant flaws in the proposed key recovery attacks. In particular, we demonstrate that the distinguisher used in impossible differential attacks by Liu et al. is ineffective for key recovery, despite their higher claimed complexities compared to ours.</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="/2024/2090.pdf"> <img class="icon" src="/img/file-pdf.svg">PDF</a> </dd> <dt>Category</dt> <dd><a href="/search?category=SECRETKEY"><small class="badge category category-SECRETKEY">Secret-key cryptography</small></a></dd> <dt>Publication info</dt> <dd>Preprint. </dd> <dt>Contact author(s)</dt> <dd><span class="font-monospace"> cheanda22<span class="obfuscate"> @ </span>mails ucas ac cn<br>shahram rasoolzadeh<span class="obfuscate"> @ </span>rub de </span> </dd> <dt>History</dt> <dd>2025-03-23: revised</dd> <dd>2024-12-29: received</dd> <dd><a rel="nofollow" href="/archive/versions/2024/2090">See all versions</a></dd> <dt>Short URL</dt> <dd><a href="https://ia.cr/2024/2090">https://ia.cr/2024/2090</a></dd> <dt>License</dt> <dd><a rel="license" target="_blank" href="https://creativecommons.org/licenses/by-nc/4.0/"> <img class="licenseImg" src="/img/license/CC_BY_NC.svg" alt="Creative Commons Attribution-NonCommercial" title="Creative Commons Attribution-NonCommercial"><br> <small>CC BY-NC</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:2024/2090, author = {Anda Che and Shahram Rasoolzadeh}, title = {Breaking the Shadow: Key Recovery Attack on Full-Round Shadow Block Ciphers with Minimal Data}, howpublished = {Cryptology {ePrint} Archive, Paper 2024/2090}, year = {2024}, url = {https://eprint.iacr.org/2024/2090} } </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>