mirror of
https://github.com/veracrypt/VeraCrypt
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130 lines
9.4 KiB
HTML
130 lines
9.4 KiB
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
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"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
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<head>
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<meta http-equiv="content-type" content="text/html; charset=utf-8" />
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<title>VeraCrypt - Free Open source disk encryption with strong security for the Paranoid</title>
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<meta name="description" content="VeraCrypt is free open-source disk encryption software for Windows, Mac OS X and Linux. In case an attacker forces you to reveal the password, VeraCrypt provides plausible deniability. In contrast to file encryption, data encryption performed by VeraCrypt is real-time (on-the-fly), automatic, transparent, needs very little memory, and does not involve temporary unencrypted files."/>
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<meta name="keywords" content="encryption, security"/>
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<link href="styles.css" rel="stylesheet" type="text/css" />
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</head>
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<body>
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<div>
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<a href="https://www.veracrypt.fr/en/Home.html"><img src="VeraCrypt128x128.png" alt="VeraCrypt"/></a>
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</div>
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<div id="menu">
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<ul>
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<li><a href="Home.html">Home</a></li>
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<li><a href="/code/">Source Code</a></li>
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<li><a href="Downloads.html">Downloads</a></li>
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<li><a class="active" href="Documentation.html">Documentation</a></li>
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<li><a href="Donation.html">Donate</a></li>
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<li><a href="https://sourceforge.net/p/veracrypt/discussion/" target="_blank">Forums</a></li>
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</ul>
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</div>
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<div>
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<p>
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<a href="Documentation.html">Documentation</a>
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<img src="arrow_right.gif" alt=">>" style="margin-top: 5px">
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<a href="Technical%20Details.html">Technical Details</a>
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<img src="arrow_right.gif" alt=">>" style="margin-top: 5px">
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<a href="Modes%20of%20Operation.html">Modes of Operation</a>
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</p></div>
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<div class="wikidoc">
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<h1>Modes of Operation</h1>
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<div style="text-align:left; margin-top:19px; margin-bottom:19px; padding-top:0px; padding-bottom:0px">
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<br style="text-align:left">
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The mode of operation used by VeraCrypt for encrypted partitions, drives, and virtual volumes is XTS.
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<br style="text-align:left">
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<br style="text-align:left">
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XTS mode is in fact XEX mode <a href="http://www.cs.ucdavis.edu/%7Erogaway/papers/offsets.pdf">
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[12]</a>, which was designed by Phillip Rogaway in 2003, with a minor modification (XEX mode uses a single key for two different purposes, whereas XTS mode uses two independent keys).<br style="text-align:left">
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<br style="text-align:left">
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In 2010, XTS mode was approved by NIST for protecting the confidentiality of data on storage devices [24]. In 2007, it was also approved by the IEEE for cryptographic protection of data on block-oriented storage devices (IEEE 1619).</div>
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<div style="text-align:left; margin-top:19px; margin-bottom:19px; padding-top:0px; padding-bottom:0px">
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</div>
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<h2 style="text-align:left; margin-top:19px; margin-bottom:19px; padding-top:0px; padding-bottom:0px">
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<strong style="text-align:left">Description of XTS mode</strong>:</h2>
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<div style="text-align:left; margin-top:19px; margin-bottom:19px; padding-top:0px; padding-bottom:0px">
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<em style="text-align:left">C<sub style="text-align:left; font-size:85%">i</sub></em> =
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<em style="text-align:left">E</em><sub style="text-align:left; font-size:85%"><em style="text-align:left">K</em>1</sub>(<em style="text-align:left">P<sub style="text-align:left; font-size:85%">i</sub></em> ^ (<em style="text-align:left">E</em><sub style="text-align:left; font-size:85%"><em style="text-align:left">K</em>2</sub>(<em style="text-align:left">n</em>)
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<img src="gf2_mul.gif" alt="" width="10" height="10">
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<em style="text-align:left">a<sup style="text-align:left; font-size:85%">i</sup></em>)) ^ (<em style="text-align:left">E</em><sub style="text-align:left; font-size:85%"><em style="text-align:left">K</em>2</sub>(<em style="text-align:left">n</em>)
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<img src="gf2_mul.gif" alt="" width="10" height="10"><em style="text-align:left"> a<sup style="text-align:left; font-size:85%">i</sup></em>)</div>
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<div style="text-align:left; margin-top:19px; margin-bottom:19px; padding-top:0px; padding-bottom:0px">
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Where:</div>
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<table style="border-collapse:separate; border-spacing:0px; width:608px; text-align:left; font-size:11px; line-height:13px; font-family:Verdana,Arial,Helvetica,sans-serif; border:0px outset #999">
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<tbody style="text-align:left">
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<tr style="text-align:left">
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<td style="vertical-align:top; color:#000000; text-align:left; font-size:11px; line-height:13px; font-family:Verdana,Arial,Helvetica,sans-serif; padding:0px">
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<sup style="text-align:left; font-size:85%"> <img src="gf2_mul.gif" alt="" width="10" height="10"></sup></td>
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<td style="vertical-align:top; color:#000000; text-align:left; font-size:11px; line-height:13px; font-family:Verdana,Arial,Helvetica,sans-serif; padding:0px">
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denotes multiplication of two polynomials over the binary field GF(2) modulo <em style="text-align:left">
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x</em><sup style="text-align:left; font-size:85%">128</sup>+<em style="text-align:left">x</em><sup style="text-align:left; font-size:85%">7</sup>+<em style="text-align:left">x</em><sup style="text-align:left; font-size:85%">2</sup>+<em style="text-align:left">x</em>+1</td>
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</tr>
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<tr style="text-align:left">
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<td style="width:30px; vertical-align:top; color:#000000; text-align:left; font-size:11px; line-height:13px; font-family:Verdana,Arial,Helvetica,sans-serif; padding:0px">
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<br style="text-align:left">
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<em style="text-align:left">K</em>1</td>
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<td style="width:578px; vertical-align:top; color:#000000; text-align:left; font-size:11px; line-height:13px; font-family:Verdana,Arial,Helvetica,sans-serif; padding:0px">
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<br style="text-align:left">
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is the encryption key (256-bit for each supported cipher; i.e, AES, Serpent, and Twofish)</td>
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</tr>
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<tr style="text-align:left">
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<td style="vertical-align:top; color:#000000; text-align:left; font-size:11px; line-height:13px; font-family:Verdana,Arial,Helvetica,sans-serif; padding:0px">
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<br style="text-align:left">
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<em style="text-align:left">K</em>2</td>
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<td style="vertical-align:top; color:#000000; text-align:left; font-size:11px; line-height:13px; font-family:Verdana,Arial,Helvetica,sans-serif; padding:0px">
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<br style="text-align:left">
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is the secondary key (256-bit for each supported cipher; i.e, AES, Serpent, and Twofish)</td>
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</tr>
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<tr style="text-align:left">
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<td style="vertical-align:top; color:#000000; text-align:left; font-size:11px; line-height:13px; font-family:Verdana,Arial,Helvetica,sans-serif; padding:0px">
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<br style="text-align:left">
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<em style="text-align:left">i</em></td>
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<td style="vertical-align:top; color:#000000; text-align:left; font-size:11px; line-height:13px; font-family:Verdana,Arial,Helvetica,sans-serif; padding:0px">
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<br style="text-align:left">
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is the cipher block index within a data unit; for the first cipher block within a data unit,
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<em style="text-align:left">i</em> = 0</td>
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</tr>
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<tr style="text-align:left">
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<td style="vertical-align:top; color:#000000; text-align:left; font-size:11px; line-height:13px; font-family:Verdana,Arial,Helvetica,sans-serif; padding:0px">
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<br style="text-align:left">
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<em style="text-align:left">n</em></td>
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<td style="vertical-align:top; color:#000000; text-align:left; font-size:11px; line-height:13px; font-family:Verdana,Arial,Helvetica,sans-serif; padding:0px">
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<br style="text-align:left">
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is the data unit index within the scope of <em style="text-align:left">K</em>1; for the first data unit,
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<em style="text-align:left">n</em> = 0</td>
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</tr>
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<tr style="text-align:left">
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<td style="vertical-align:top; color:#000000; text-align:left; font-size:11px; line-height:13px; font-family:Verdana,Arial,Helvetica,sans-serif; padding:0px">
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<br style="text-align:left">
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<em style="text-align:left">a</em></td>
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<td style="vertical-align:top; color:#000000; text-align:left; font-size:11px; line-height:13px; font-family:Verdana,Arial,Helvetica,sans-serif; padding:0px">
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<br style="text-align:left">
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is a primitive element of Galois Field (2<sup style="text-align:left; font-size:85%">128</sup>) that corresponds to polynomial
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<em style="text-align:left">x</em> (i.e., 2)</td>
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</tr>
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<tr style="text-align:left">
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<td colspan="2" style="vertical-align:top; color:#000000; text-align:left; font-size:11px; line-height:13px; font-family:Verdana,Arial,Helvetica,sans-serif; padding:0px">
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<br style="text-align:left">
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<span style="text-align:left; font-size:10px; line-height:12px">Note: The remaining symbols are defined in the section
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<a href="Notation.html" style="text-align:left; color:#0080c0; text-decoration:none.html">
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Notation</a>. </span></td>
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</tr>
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</tbody>
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</table>
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<div style="text-align:left; margin-top:19px; margin-bottom:19px; padding-top:0px; padding-bottom:0px">
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<br style="text-align:left">
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The size of each data unit is always 512 bytes (regardless of the sector size).</div>
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<div style="text-align:left; margin-top:19px; margin-bottom:19px; padding-top:0px; padding-bottom:0px">
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For further information pertaining to XTS mode, see e.g. <a href="http://www.cs.ucdavis.edu/%7Erogaway/papers/offsets.pdf" style="text-align:left; color:#0080c0; text-decoration:none">
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[12]</a> and <a href="http://csrc.nist.gov/publications/nistpubs/800-38E/nist-sp-800-38E.pdf" style="text-align:left; color:#0080c0; text-decoration:none">
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[24]</a>.</div>
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<div style="text-align:left; margin-top:19px; margin-bottom:19px; padding-top:0px; padding-bottom:0px">
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<a href="Header%20Key%20Derivation.html" style="text-align:left; color:#0080c0; text-decoration:none; font-weight:bold.html">Next Section >></a></div>
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</div><div class="ClearBoth"></div></body></html>
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