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Documentation: Add entry about KDF, PBKDF2.
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Mounir IDRASSI
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doc/html/en/Argon2id.html
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doc/html/en/Argon2id.html
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<!DOCTYPE html>
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<html 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="Documentation.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.html">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="Key%20Derivation%20Algorithms.html">Key Derivation Algorithms</a>
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<img src="arrow_right.gif" alt=">>" style="margin-top: 5px">
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<a href="Argon2id.html">Argon2id</a>
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</p></div>
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<div class="wikidoc">
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<h1>Argon2id</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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Argon2id is a memory-hard key derivation function designed to resist both time-memory trade-off attacks and side-channel attacks. It was selected as the winner of the Password Hashing Competition (PHC) in 2015 and is defined in RFC 9106. VeraCrypt supports Argon2id as an alternative to PBKDF2-HMAC for header key derivation.
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</div>
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<h3>Key Features</h3>
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<ul style="text-align:left; margin-top:18px; margin-bottom:19px; padding-top:0px; padding-bottom:0px">
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<li style="text-align:left; margin-top:0px; margin-bottom:0px; padding-top:0px; padding-bottom:0px">
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<strong>Memory-hard:</strong> Requires a configurable amount of memory, making it resistant to specialized hardware attacks
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</li>
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<li style="text-align:left; margin-top:0px; margin-bottom:0px; padding-top:0px; padding-bottom:0px">
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<strong>Side-channel resistant:</strong> Combines data-dependent and data-independent memory access patterns
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</li>
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<li style="text-align:left; margin-top:0px; margin-bottom:0px; padding-top:0px; padding-bottom:0px">
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<strong>Internal hash function:</strong> Uses BLAKE2b internally, eliminating the need for separate hash algorithm selection
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</li>
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<li style="text-align:left; margin-top:0px; margin-bottom:0px; padding-top:0px; padding-bottom:0px">
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<strong>Tunable parameters:</strong> Allows adjustment of memory cost, time cost, and parallelism
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</li>
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</ul>
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<h3>Argon2 Variants</h3>
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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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Argon2 has three variants:
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</div>
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<ul style="text-align:left; margin-top:18px; margin-bottom:19px; padding-top:0px; padding-bottom:0px">
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<li style="text-align:left; margin-top:0px; margin-bottom:0px; padding-top:0px; padding-bottom:0px">
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<strong>Argon2d:</strong> Uses data-dependent memory access, resistant to time-memory trade-off attacks but vulnerable to side-channel attacks
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</li>
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<li style="text-align:left; margin-top:0px; margin-bottom:0px; padding-top:0px; padding-bottom:0px">
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<strong>Argon2i:</strong> Uses data-independent memory access, resistant to side-channel attacks but more vulnerable to time-memory trade-off attacks
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</li>
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<li style="text-align:left; margin-top:0px; margin-bottom:0px; padding-top:0px; padding-bottom:0px">
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<strong>Argon2id:</strong> Hybrid approach that combines both variants, providing resistance to both attack types (used by VeraCrypt)
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</li>
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</ul>
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<h3>Parameters in VeraCrypt</h3>
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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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VeraCrypt uses Argon2id with the following parameter configuration:
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</div>
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<h4>Memory Cost (m_cost)</h4>
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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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The amount of memory used during the key derivation process, controlled by the PIM value:
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</div>
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<ul style="text-align:left; margin-top:18px; margin-bottom:19px; padding-top:0px; padding-bottom:0px">
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<li style="text-align:left; margin-top:0px; margin-bottom:0px; padding-top:0px; padding-bottom:0px">
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<strong>Formula:</strong> m_cost(pim) = min(64 MiB + (pim - 1) × 32 MiB, 1024 MiB)
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</li>
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<li style="text-align:left; margin-top:0px; margin-bottom:0px; padding-top:0px; padding-bottom:0px">
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<strong>Range:</strong> 64 MiB to 1024 MiB (capped at PIM = 31)
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</li>
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<li style="text-align:left; margin-top:0px; margin-bottom:0px; padding-top:0px; padding-bottom:0px">
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<strong>Default:</strong> 96 MiB (equivalent to PIM = 2)
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</li>
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</ul>
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<h4>Time Cost (t_cost)</h4>
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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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The number of iterations performed during the key derivation process:
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</div>
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<ul style="text-align:left; margin-top:18px; margin-bottom:19px; padding-top:0px; padding-bottom:0px">
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<li style="text-align:left; margin-top:0px; margin-bottom:0px; padding-top:0px; padding-bottom:0px">
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<strong>For PIM ≤ 31:</strong> t_cost(pim) = 3 + floor((pim - 1) / 3)
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</li>
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<li style="text-align:left; margin-top:0px; margin-bottom:0px; padding-top:0px; padding-bottom:0px">
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<strong>For PIM > 31:</strong> t_cost(pim) = 13 + (pim - 31)
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</li>
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<li style="text-align:left; margin-top:0px; margin-bottom:0px; padding-top:0px; padding-bottom:0px">
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<strong>Default:</strong> 3 iterations (equivalent to PIM = 2)
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</li>
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</ul>
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<h4>Parallelism</h4>
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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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The number of parallel threads used during computation:
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</div>
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<ul style="text-align:left; margin-top:18px; margin-bottom:19px; padding-top:0px; padding-bottom:0px">
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<li style="text-align:left; margin-top:0px; margin-bottom:0px; padding-top:0px; padding-bottom:0px">
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<strong>Value:</strong> Fixed at 1 thread for all cases in VeraCrypt
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</li>
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<li style="text-align:left; margin-top:0px; margin-bottom:0px; padding-top:0px; padding-bottom:0px">
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<strong>Rationale:</strong> Ensures consistent behavior across different hardware configurations
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</li>
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</ul>
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<h3>Advantages over PBKDF2</h3>
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<ul style="text-align:left; margin-top:18px; margin-bottom:19px; padding-top:0px; padding-bottom:0px">
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<li style="text-align:left; margin-top:0px; margin-bottom:0px; padding-top:0px; padding-bottom:0px">
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<strong>Memory hardness:</strong> Requires significant memory allocation, making GPU and ASIC attacks more expensive
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</li>
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<li style="text-align:left; margin-top:0px; margin-bottom:0px; padding-top:0px; padding-bottom:0px">
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<strong>Modern design:</strong> Specifically designed to resist contemporary attack methods
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</li>
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<li style="text-align:left; margin-top:0px; margin-bottom:0px; padding-top:0px; padding-bottom:0px">
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<strong>Side-channel resistance:</strong> Built-in protections against cache-timing and other side-channel attacks
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</li>
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<li style="text-align:left; margin-top:0px; margin-bottom:0px; padding-top:0px; padding-bottom:0px">
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<strong>Standardization:</strong> Officially standardized in RFC 9106
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</li>
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</ul>
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<h3>Usage Considerations</h3>
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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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When using Argon2id in VeraCrypt:
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</div>
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<ul style="text-align:left; margin-top:18px; margin-bottom:19px; padding-top:0px; padding-bottom:0px">
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<li style="text-align:left; margin-top:0px; margin-bottom:0px; padding-top:0px; padding-bottom:0px">
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<strong>Memory requirements:</strong> Ensure sufficient RAM is available, especially with higher PIM values
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</li>
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<li style="text-align:left; margin-top:0px; margin-bottom:0px; padding-top:0px; padding-bottom:0px">
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<strong>Performance:</strong> Higher memory costs may result in slower mounting times but provide better security
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</li>
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<li style="text-align:left; margin-top:0px; margin-bottom:0px; padding-top:0px; padding-bottom:0px">
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<strong>Compatibility:</strong> Available in VeraCrypt versions that support multiple key derivation functions
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</li>
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<li style="text-align:left; margin-top:0px; margin-bottom:0px; padding-top:0px; padding-bottom:0px">
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<strong>No hash selection:</strong> Unlike PBKDF2-HMAC, no separate hash algorithm needs to be chosen
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</li>
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</ul>
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<h3>Technical Specifications</h3>
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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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<strong>Algorithm:</strong> Argon2id as defined in RFC 9106<br/>
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<strong>Internal hash:</strong> BLAKE2b<br/>
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<strong>Salt size:</strong> 512 bits (same as PBKDF2-HMAC)<br/>
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<strong>Output length:</strong> Variable, depending on the encryption algorithm (e.g., 256 bits for AES-256, 768 bits for AES-Twofish-Serpent cascade)<br/>
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<strong>Version:</strong> Argon2 version 0x13 (19 decimal)
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</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 more information about PIM values and their effect on Argon2id parameters, see the
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<a href="Personal%20Iterations%20Multiplier%20%28PIM%29.html" style="text-align:left; color:#0080c0; text-decoration:none">
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Personal Iterations Multiplier (PIM)</a> section.
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</div>
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</div><div class="ClearBoth"></div></body></html>
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