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EverCryptCTR.html
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<div class="section" id="ctr-mode-encryption-evercrypt-ctr-h">
<h1>CTR-mode encryption (<code class="docutils literal notranslate"><span class="pre">EverCrypt_CTR.h</span></code>)<a class="headerlink" href="#ctr-mode-encryption-evercrypt-ctr-h" title="Permalink to this headline">¶</a></h1>
<div class="admonition warning">
<p class="first admonition-title">Warning</p>
<p class="last">Using encryption without a MAC is potentially <strong>dangerous</strong>. We recommend users
stick with the AEAD API.</p>
</div>
<div class="admonition warning">
<p class="first admonition-title">Warning</p>
<p><strong>This API is a work-in-progress and is not fully verified.</strong> If you need it
for something serious, let us know and we’ll prioritize.</p>
<ul class="last simple">
<li>It doesn’t multiplex across all implementations of Chacha</li>
<li>It doesn’t offer complete encryption, only block-by-block</li>
<li>It has no streaming API</li>
</ul>
</div>
<p>This API is:</p>
<ul class="simple">
<li><strong>agile</strong></li>
<li><strong>multiplexing</strong>: portable C (Chacha); AESNI + CLMUL (AES128, AES256)</li>
<li><strong>stateful</strong></li>
</ul>
<p>Possible values for the agility argument (<code class="docutils literal notranslate"><span class="pre">Hacl_Spec.h</span></code>) :</p>
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span>
<span class="cp">#define Spec_Agile_Cipher_AES128 0</span>
<span class="cp">#define Spec_Agile_Cipher_AES256 1</span>
<span class="cp">#define Spec_Agile_Cipher_CHACHA20 2</span>
</pre></div>
</div>
<p>Supported values for the agility argument: all</p>
<div class="section" id="state-management">
<h2>State management<a class="headerlink" href="#state-management" title="Permalink to this headline">¶</a></h2>
<p>Clients are first expected to allocate persistent state via <code class="docutils literal notranslate"><span class="pre">create_in</span></code>, which
stores the expanded key along with the current value of the counter.</p>
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span>
<span class="n">EverCrypt_Error_error_code</span><span class="w"></span>
<span class="nf">EverCrypt_CTR_create_in</span><span class="p">(</span><span class="w"></span>
<span class="w"> </span><span class="n">Spec_Agile_Cipher_cipher_alg</span><span class="w"> </span><span class="n">a</span><span class="p">,</span><span class="w"></span>
<span class="w"> </span><span class="n">EverCrypt_CTR_state_s</span><span class="w"> </span><span class="o">**</span><span class="n">dst</span><span class="p">,</span><span class="w"></span>
<span class="w"> </span><span class="kt">uint8_t</span><span class="w"> </span><span class="o">*</span><span class="n">k</span><span class="p">,</span><span class="w"></span>
<span class="w"> </span><span class="kt">uint8_t</span><span class="w"> </span><span class="o">*</span><span class="n">iv</span><span class="p">,</span><span class="w"></span>
<span class="w"> </span><span class="kt">uint32_t</span><span class="w"> </span><span class="n">iv_len</span><span class="p">,</span><span class="w"></span>
<span class="w"> </span><span class="kt">uint32_t</span><span class="w"> </span><span class="n">c</span><span class="w"></span>
<span class="p">);</span><span class="w"></span>
</pre></div>
</div>
<p>The expected usage for <code class="docutils literal notranslate"><span class="pre">create_in</span></code> is similar to <code class="docutils literal notranslate"><span class="pre">EverCrypt_AEAD_create_in</span></code>,
except arbitrary-length IVs are not supported; IV lengths must satisfy the
<code class="docutils literal notranslate"><span class="pre">nounce_bound</span></code> predicate from <code class="docutils literal notranslate"><span class="pre">Spec.Agile.CTR.fsti</span></code>. Clients are also
expected to pass the initial value of the counter.</p>
<p>State can be reset to a different IV and counter value using the <code class="docutils literal notranslate"><span class="pre">init</span></code>
function. (This function really should be called <code class="docutils literal notranslate"><span class="pre">reset</span></code>.)</p>
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span>
<span class="kt">void</span><span class="w"></span>
<span class="nf">EverCrypt_CTR_init</span><span class="p">(</span><span class="w"></span>
<span class="w"> </span><span class="n">EverCrypt_CTR_state_s</span><span class="w"> </span><span class="o">*</span><span class="n">p</span><span class="p">,</span><span class="w"></span>
<span class="w"> </span><span class="kt">uint8_t</span><span class="w"> </span><span class="o">*</span><span class="n">k</span><span class="p">,</span><span class="w"></span>
<span class="w"> </span><span class="kt">uint8_t</span><span class="w"> </span><span class="o">*</span><span class="n">iv</span><span class="p">,</span><span class="w"></span>
<span class="w"> </span><span class="kt">uint32_t</span><span class="w"> </span><span class="n">iv_len</span><span class="p">,</span><span class="w"></span>
<span class="w"> </span><span class="kt">uint32_t</span><span class="w"> </span><span class="n">c</span><span class="w"></span>
<span class="p">);</span><span class="w"></span>
</pre></div>
</div>
<p>State <strong>must</strong> be called via <code class="docutils literal notranslate"><span class="pre">free</span></code>.</p>
</div>
<div class="section" id="ctr-mode-of-operation">
<h2>CTR mode of operation<a class="headerlink" href="#ctr-mode-of-operation" title="Permalink to this headline">¶</a></h2>
<p>The <code class="docutils literal notranslate"><span class="pre">update_block</span></code> function encrypts a block-sized piece of data using the CTR
mode, and internally increments the state by one.</p>
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span>
<span class="kt">void</span><span class="w"> </span><span class="nf">EverCrypt_CTR_update_block</span><span class="p">(</span><span class="n">EverCrypt_CTR_state_s</span><span class="w"> </span><span class="o">*</span><span class="n">p</span><span class="p">,</span><span class="w"> </span><span class="kt">uint8_t</span><span class="w"> </span><span class="o">*</span><span class="n">dst</span><span class="p">,</span><span class="w"> </span><span class="kt">uint8_t</span><span class="w"> </span><span class="o">*</span><span class="n">src</span><span class="p">);</span><span class="w"></span>
</pre></div>
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