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<!DOCTYPE html>
<html lang="en">
<head>
m4_include(head.html)
</head>
<body>
<header>
<div>
<h1>Easy Password Generation</h1>
m4_include(nav.html)
</div>
<figure class="quote">
<blockquote>
<p>The C preprocessor is worse than m4, and I would kill myself
before I had to use m4.</p>
</blockquote>
<figcaption>
Arav K.
</figcaption>
</figure>
</header>
<main>
<p>
<em>
You can find the <code>totp</code> git repository over at
<a href="https://git.sr.ht/~mango/totp" target="_blank">sourcehut</a>
or <a href="https://github.com/Mango0x45/totp"
target="_blank">GitHub</a>.
</em>
</p>
<h2>Table of Contents</h2>
<ul>
<li><a href="#prologue">Prologue</a></li>
<li><a href="#terms">Terminology</a></li>
<li><a href="#usage">Basic Usage</a></li>
<li><a href="#qr">Working with QR Codes</a></li>
</ul>
<h2 id="prologue">Prologue</h2>
<p>
<abbr class="totp">TOTP</abbr> codes are pretty cool, and really easy to
do. They’re also the backbone of modern two-factor authentication.
With <code>totp</code> I hope to make
handling <abbr class="totp">TOTP</abbr> codes as easy and extensible as
possible.
</p>
<h2 id="terms">Terminology</h2>
<p>
There are a few terms that I will be using throughout this post, so it’s
good to make sure that we’re all on the same page about what I’m
referring to.
</p>
<dl>
<dt>Secret</dt>
<dd>
<p>
Your <em>secret</em> is
a <a href="https://en.wikipedia.org/wiki/Base32"
target="_blank">base32</a> encoded secret key that you should under
no circumstances share with anyone else. It is from this secret key
that we can generate valid <abbr class="totp">TOTP</abbr> codes.
</p>
</dd>
<dt>Digits</dt>
<dd>
<p>
Your <em>digits</em> is the length of the generated
<abbr class="totp">TOTP</abbr> in digits. If <em>digits</em> is 8,
then your generated key could be ‘01234567’. When dealing
with <abbr class="tfa">2FA</abbr> this is typically 6.
</p>
</dd>
<dt>Period</dt>
<dd>
<p>
Your <em>period</em> it the duration for which the generated key is
valid in seconds. When working with <abbr class="tfa">2FA</abbr>
this is typically 30.
</p>
</dd>
</dl>
<h2 id="usage">Basic Usage</h2>
<p>
<code>totp</code> takes secret keys as command-line arguments, but also
reads them from the standard input if none are provided. It assumes
that <em>digits</em> is 6 and <em>period</em> is 30. These defaults can
be changed with the <code>-d</code> and <code>-p</code> flags.
</p>
<figure>
<pre>m4_fmt_code(basic-usage.sh.html)</pre>
</figure>
<aside>
<p>
I’m using <code>mkpass</code> to generate a random secret. You can
see my post about <code>mkpass</code> <a href="/prj/mkpass">here</a>.
</p>
</aside>
<h2 id="qr">Working with <abbr class="qr">QR</abbr> Codes</h2>
<p>
Often times when enabling <abbr class="tfa">2FA</abbr> on your account
on some website or platform, you will be shown
a <abbr class="qr">QR</abbr> code you can scan with
your <abbr class="">2FA</abbr> mobile application.
These <abbr class="qr">QR</abbr> codes
contain <em>otpauth</em> <abbr class="uri">URI</abbr>s. We can extract
these from downloaded images using utilities such
as <code>zbarimg</code> and use them in <code>totp</code> using
the <code>-u</code> flag to enable ‘<abbr class="uri">URI</abbr> mode’
</p>
<figure>
<pre>m4_fmt_code(zbarimg.sh.html)</pre>
</figure>
…and that’s all! There’s nothing else you need. You can use secret keys
and otpauth <abbr class="uri">URI</abbr>s, and you can configure
the <em>digits</em> and <em>period</em> of the generated codes. You can
generate multiple keys at once, and all outputs are printed to the
standard output.
</main>
<hr>
<footer>
m4_footer
</footer>
</body>
</html>
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