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2024-04-07 01:04:16 -04:00
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<title>TOTP.fyi — A TOTP Code Generator for Developers</title>
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2024-04-07 01:04:16 -04:00
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<a class="navbar-brand" href="#">TOTP.fyi</a>
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<a class="nav-link" href="#what-is-this">What is this?</a>
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<a class="nav-link" href="#how-to-use">How to use?</a>
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<li class="nav-item">
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<a class="nav-link" href="#how-does-it-work">How does it work?</a>
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<a class="nav-link" href="#support-me">Support me</a>
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2024-04-07 01:04:16 -04:00
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<main class="container">
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<noscript>You need to enable JavaScript to run this app.</noscript>
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<div class="jumbotron">
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<p class="lead">This is a code generator for the Time-based One Time Password (TOTP) algorithm.</p>
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<hr>
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<div id="root"></div>
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</div>
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</main>
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2024-04-13 17:35:20 -04:00
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<div class="container totp-about">
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<div class="card">
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<div class="card-body">
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<h3 class="card-title" id="what-is-this">What is this?</h3>
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<p class="card-text">This is a code generator for the <a
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href="https://en.wikipedia.org/wiki/Time-based_One_Time_Password"><em>Time-based One Time Password</em>
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(TOTP)</a> algorithm. It's intended for developers of web applications with TOTP support to quickly generate
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codes for testing purposes. It's <strong>not</strong> meant to be a general purpose authenticator app.
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</p>
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<p class="card-text">What this tool can do:</p>
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<ul class="card-text">
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<li>Quickly generate TOTP codes;</li>
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<li>View codes for past and future time windows; and</li>
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<li>Fiddle with various TOTP parameters.</li>
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</ul>
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<p class="card-text">What this tool <strong>can't</strong> do:</p>
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<ul class="card-text">
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<li>Store your TOTP secrets (you can try bookmarking this page with the secret in the URL, but it's not
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secure);
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</li>
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<li>Act as your general purpose authenticator app; and</li>
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<li>Scan TOTP QR codes.</li>
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</ul>
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</div>
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</div>
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<div class="card">
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<div class="card-body">
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<h3 class="card-title" id="how-to-use">How do I use this tool?</h3>
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<p class="card-text">To start, simply type or paste in the TOTP secret key. This should be in the standard base32
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format. This will generate 6-digit TOTP codes that update every 30 seconds using the SHA-1 algorithm that's used
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by default in all major authenticator apps.
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</p>
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<p class="card-text">You can press "show advanced settings" to adjust the TOTP parameters to use non-default
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values.
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</p>
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<p class="card-text">The generated codes are displayed in chronological order. The current code is shown in large
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text. The codes above are past codes, and the codes below are future codes.</p>
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<p class="card-text">The settings are stored in the URL hash. You can bookmark the page or copy the link to go
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directly to a certain configuration.</p>
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</div>
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</div>
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2025-02-16 16:42:09 -05:00
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<div class="card">
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<div class="card-body">
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<h3 class="card-title" id="how-does-it-work">How does TOTP work?</h3>
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<p class="card-text">Time-based one-time password (TOTP), defined in <a
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href="https://datatracker.ietf.org/doc/html/rfc6238">RFC 6238</a>, is based on the HMAC-based one-time password
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(HOTP) algorithm, which uses the common HMAC construction based on the current time. TOTP requires the following
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inputs:
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</p>
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<ul class="card-text">
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<li>The cryptographic hash function <var>H</var>, which defaults to SHA-1. This is configurable in the advanced
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settings;
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</li>
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<li>The secret key <var>K</var>, which is commonly encoded as Base32. This value, encoded in Base32, is what you
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enter into the <strong>secret key</strong> field;
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</li>
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<li>The time window <var>X</var>, which is how long each code is valid for;</li>
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<li>The epoch <var>T<sub>0</sub></var>, which is the Unix epoch (0 in Unix time) in every known implementation,
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but could be changed; and
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</li>
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<li>The number of digits <var>d</var>, which is the length of the final output code in decimal digits.</li>
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</ul>
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<p class="card-text">The algorithm is as follows:</p>
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<ol class="card-text">
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<li>Take the current unix time <var>U</var>;</li>
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<li>Compute the time step count
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<img class="math" src="math/t.svg" alt="T=\left\lfloor\frac{U - T_0}{X}\right\rfloor" height="40">;
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</li>
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<li>Compute the HMAC <img class="math" src="math/h.svg" alt="h = \text{HMAC}_H(K, T)" height="18">;</li>
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<li>Extract the 4 lowest order bits, i.e. the 4 least significant bits from the last byte of <var>h</var>, to
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create the integer <var>i</var>;
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</li>
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<li>Take four bytes from <var>h</var> starting at <var>i</var>, i.e. bytes [<var>i</var>, <var>i</var>+4), mask
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off the most significant bit (to support signed arithmetic), and use it to create the integer <var>y</var>;
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and finally
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</li>
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<li>Compute the code as <img class="math" src="math/mod.svg" alt="y \bmod{10^d}" height="18"
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style="vertical-align: -3px">, zero-padded to <var>d</var> digits.
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</li>
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</ol>
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<p class="card-text">Express as Python code, the last 3 steps would look like:</p>
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<pre class="highlight"><code><span class="n">i</span> <span class="o">=</span> <span class="n">h</span><span
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class="p">[</span><span class="o">-</span><span class="mi">1</span><span class="p">]</span> <span class="o">&</span> <span
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class="mh">0xF</span>
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<span class="n">y</span> <span class="o">=</span> <span class="p">(</span>
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<span class="p">(</span><span class="n">h</span><span class="p">[</span><span class="n">i</span> <span
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class="o">+</span> <span class="mi">0</span><span class="p">]</span> <span class="o">&</span> <span
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class="mh">0x7F</span><span class="p">)</span> <span class="o"><<</span> <span
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class="mi">24</span> <span class="o">|</span>
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<span class="p">(</span><span class="n">h</span><span class="p">[</span><span class="n">i</span> <span
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class="o">+</span> <span class="mi">1</span><span class="p">]</span> <span class="o">&</span> <span
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class="mh">0xFF</span><span class="p">)</span> <span class="o"><<</span> <span
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class="mi">16</span> <span class="o">|</span>
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<span class="p">(</span><span class="n">h</span><span class="p">[</span><span class="n">i</span> <span
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class="o">+</span> <span class="mi">2</span><span class="p">]</span> <span class="o">&</span> <span
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class="mh">0xFF</span><span class="p">)</span> <span class="o"><<</span> <span class="mi">8</span> <span
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class="o">|</span>
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<span class="p">(</span><span class="n">h</span><span class="p">[</span><span class="n">i</span> <span
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class="o">+</span> <span class="mi">3</span><span class="p">]</span> <span class="o">&</span> <span
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class="mh">0xFF</span><span class="p">)</span>
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<span class="p">)</span>
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<span class="n">code</span> <span class="o">=</span> <span class="nb">str</span><span class="p">(</span><span class="n">y</span> <span
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class="o">%</span> <span class="mi">10</span><span class="o">**</span><span class="n">d</span><span class="p">)</span><span
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class="o">.</span><span class="n">rjust</span><span class="p">(</span><span class="n">d</span><span class="p">,</span> <span
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class="s1">'0'</span><span class="p">)</span>
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</code></pre>
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<p class="card-text">To avoid clock synchronization issues, most implementations will accept TOTP codes from the
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window before and after the one based on the current time. This tool lets you see the previous and next codes to
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help you debug.</p>
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</div>
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</div>
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2025-02-10 12:17:47 -05:00
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<h3 class="card-title" id="support-me">I like this website. How can I support you?</h3>
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For security reasons, this website will <b>NEVER</b> serve ads. Unfortunately, servers and domains are not free,
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though I try to be as economical as I can. I would rather lose money running this public service than serve
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ads or shut it down, but if you would like to help me offset the costs, feel free to send some money my way
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on:
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</ul>
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2024-04-13 17:35:20 -04:00
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</div>
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</div>
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2025-02-10 12:17:47 -05:00
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<footer class="footer">
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<div class="container">
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<p class="text-muted">Copyright © 2024-__YEAR__ <a href="https://quantum5.ca">Quantum</a>. Licensed under
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<a href="https://www.gnu.org/licenses/agpl-3.0.en.html">GNU AGPLv3</a>. Source code available on
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<a href="https://github.com/quantum5/totp">GitHub</a>.<br>
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Available on clearnet at <a href="https://totp.fyi">totp.fyi</a>.<br>
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Available over Tor at
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<a href="http://totpfyiis63jxz5k5gv6uqb3kzzm6mq6htgdszfqc73xv5p4tzrxv7qd.onion/">
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totpfyi<wbr>is63jxz5<wbr>k5gv6uqb<wbr>3kzzm6mq<wbr>6htgdszf<wbr>qc73xv5p<wbr>4tzrxv7qd.onion</a>.
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</p>
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</div>
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</footer>
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2024-04-07 01:04:16 -04:00
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<script type="module" src="/src/main.tsx"></script>
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</body>
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2024-04-06 22:54:44 -04:00
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</html>
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