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<h1 class='fqn'><span class='in-band'>Function <a href='../index.html'>crypto</a>::<wbr><a href='index.html'>sha2</a>::<wbr><a class="fn" href=''>sha256_digest_block</a></span><span class='out-of-band'><span id='render-detail'>
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</span><a class='srclink' href='../../src/crypto/sha2.rs.html#351-356' title='goto source code'>[src]</a></span></h1>
<pre class='rust fn'>pub fn sha256_digest_block(state: &amp;mut <a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.array.html">[</a><a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.u32.html">u32</a><a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.array.html">; 8]</a>, block: <a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.slice.html">&amp;[</a><a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.u8.html">u8</a><a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.slice.html">]</a>)</pre><div class='docblock'><p>Process a block with the SHA-256 algorithm. (See more...)</p>
<p>Internally, this uses functions which resemble the new Intel SHA instruction sets,
and so it&#39;s data locality properties may improve performance. However, to benefit
the most from this implementation, replace these functions with x86 intrinsics to
get a possible speed boost.</p>
<h1 id='implementation' class='section-header'><a href='#implementation'>Implementation</a></h1>
<p>The <code>Sha256</code> algorithm is implemented with functions that resemble the new
Intel SHA instruction set extensions. These intructions fall into two categories:
message schedule calculation, and the message block 64-round digest calculation.
The schedule-related instructions allow 4 rounds to be calculated as:</p>
<pre class="rust rust-example-rendered">
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">simd</span>::<span class="ident">u32x4</span>;
<span class="kw">use</span> <span class="self">self</span>::<span class="ident">crypto</span>::<span class="ident">sha2</span>::{
<span class="ident">sha256msg1</span>,
<span class="ident">sha256msg2</span>,
<span class="ident">sha256load</span>
};
<span class="kw">fn</span> <span class="ident">schedule4_data</span>(<span class="ident">work</span>: <span class="kw-2">&amp;</span><span class="kw-2">mut</span> [<span class="ident">u32x4</span>], <span class="ident">w</span>: <span class="kw-2">&amp;</span>[<span class="ident">u32</span>]) {
<span class="comment">// this is to illustrate the data order</span>
<span class="ident">work</span>[<span class="number">0</span>] <span class="op">=</span> <span class="ident">u32x4</span>(<span class="ident">w</span>[<span class="number">3</span>], <span class="ident">w</span>[<span class="number">2</span>], <span class="ident">w</span>[<span class="number">1</span>], <span class="ident">w</span>[<span class="number">0</span>]);
<span class="ident">work</span>[<span class="number">1</span>] <span class="op">=</span> <span class="ident">u32x4</span>(<span class="ident">w</span>[<span class="number">7</span>], <span class="ident">w</span>[<span class="number">6</span>], <span class="ident">w</span>[<span class="number">5</span>], <span class="ident">w</span>[<span class="number">4</span>]);
<span class="ident">work</span>[<span class="number">2</span>] <span class="op">=</span> <span class="ident">u32x4</span>(<span class="ident">w</span>[<span class="number">11</span>], <span class="ident">w</span>[<span class="number">10</span>], <span class="ident">w</span>[<span class="number">9</span>], <span class="ident">w</span>[<span class="number">8</span>]);
<span class="ident">work</span>[<span class="number">3</span>] <span class="op">=</span> <span class="ident">u32x4</span>(<span class="ident">w</span>[<span class="number">15</span>], <span class="ident">w</span>[<span class="number">14</span>], <span class="ident">w</span>[<span class="number">13</span>], <span class="ident">w</span>[<span class="number">12</span>]);
}
<span class="kw">fn</span> <span class="ident">schedule4_work</span>(<span class="ident">work</span>: <span class="kw-2">&amp;</span><span class="kw-2">mut</span> [<span class="ident">u32x4</span>], <span class="ident">t</span>: <span class="ident">usize</span>) {
<span class="comment">// this is the core expression</span>
<span class="ident">work</span>[<span class="ident">t</span>] <span class="op">=</span> <span class="ident">sha256msg2</span>(<span class="ident">sha256msg1</span>(<span class="ident">work</span>[<span class="ident">t</span> <span class="op">-</span> <span class="number">4</span>], <span class="ident">work</span>[<span class="ident">t</span> <span class="op">-</span> <span class="number">3</span>]) <span class="op">+</span>
<span class="ident">sha256load</span>(<span class="ident">work</span>[<span class="ident">t</span> <span class="op">-</span> <span class="number">2</span>], <span class="ident">work</span>[<span class="ident">t</span> <span class="op">-</span> <span class="number">1</span>]),
<span class="ident">work</span>[<span class="ident">t</span> <span class="op">-</span> <span class="number">1</span>])
}</pre>
<p>instead of 4 rounds of:</p>
<pre class="rust rust-example-rendered">
<span class="kw">fn</span> <span class="ident">schedule_work</span>(<span class="ident">w</span>: <span class="kw-2">&amp;</span><span class="kw-2">mut</span> [<span class="ident">u32</span>], <span class="ident">t</span>: <span class="ident">usize</span>) {
<span class="ident">w</span>[<span class="ident">t</span>] <span class="op">=</span> <span class="macro">sigma1</span><span class="macro">!</span>(<span class="ident">w</span>[<span class="ident">t</span> <span class="op">-</span> <span class="number">2</span>]) <span class="op">+</span> <span class="ident">w</span>[<span class="ident">t</span> <span class="op">-</span> <span class="number">7</span>] <span class="op">+</span> <span class="macro">sigma0</span><span class="macro">!</span>(<span class="ident">w</span>[<span class="ident">t</span> <span class="op">-</span> <span class="number">15</span>]) <span class="op">+</span> <span class="ident">w</span>[<span class="ident">t</span> <span class="op">-</span> <span class="number">16</span>];
}</pre>
<p>and the digest-related instructions allow 4 rounds to be calculated as:</p>
<pre class="rust rust-example-rendered">
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">simd</span>::<span class="ident">u32x4</span>;
<span class="kw">use</span> <span class="self">self</span>::<span class="ident">crypto</span>::<span class="ident">sha2</span>::{<span class="ident">K32X4</span>,
<span class="ident">sha256rnds2</span>,
<span class="ident">sha256swap</span>
};
<span class="kw">fn</span> <span class="ident">rounds4</span>(<span class="ident">state</span>: <span class="kw-2">&amp;</span><span class="kw-2">mut</span> [<span class="ident">u32</span>; <span class="number">8</span>], <span class="ident">work</span>: <span class="kw-2">&amp;</span><span class="kw-2">mut</span> [<span class="ident">u32x4</span>], <span class="ident">t</span>: <span class="ident">usize</span>) {
<span class="kw">let</span> [<span class="ident">a</span>, <span class="ident">b</span>, <span class="ident">c</span>, <span class="ident">d</span>, <span class="ident">e</span>, <span class="ident">f</span>, <span class="ident">g</span>, <span class="ident">h</span>]: [<span class="ident">u32</span>; <span class="number">8</span>] <span class="op">=</span> <span class="kw-2">*</span><span class="ident">state</span>;
<span class="comment">// this is to illustrate the data order</span>
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">abef</span> <span class="op">=</span> <span class="ident">u32x4</span>(<span class="ident">a</span>, <span class="ident">b</span>, <span class="ident">e</span>, <span class="ident">f</span>);
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">cdgh</span> <span class="op">=</span> <span class="ident">u32x4</span>(<span class="ident">c</span>, <span class="ident">d</span>, <span class="ident">g</span>, <span class="ident">h</span>);
<span class="kw">let</span> <span class="ident">temp</span> <span class="op">=</span> <span class="ident">K32X4</span>[<span class="ident">t</span>] <span class="op">+</span> <span class="ident">work</span>[<span class="ident">t</span>];
<span class="comment">// this is the core expression</span>
<span class="ident">cdgh</span> <span class="op">=</span> <span class="ident">sha256rnds2</span>(<span class="ident">cdgh</span>, <span class="ident">abef</span>, <span class="ident">temp</span>);
<span class="ident">abef</span> <span class="op">=</span> <span class="ident">sha256rnds2</span>(<span class="ident">abef</span>, <span class="ident">cdgh</span>, <span class="ident">sha256swap</span>(<span class="ident">temp</span>));
<span class="kw-2">*</span><span class="ident">state</span> <span class="op">=</span> [<span class="ident">abef</span>.<span class="number">0</span>, <span class="ident">abef</span>.<span class="number">1</span>, <span class="ident">cdgh</span>.<span class="number">0</span>, <span class="ident">cdgh</span>.<span class="number">1</span>,
<span class="ident">abef</span>.<span class="number">2</span>, <span class="ident">abef</span>.<span class="number">3</span>, <span class="ident">cdgh</span>.<span class="number">2</span>, <span class="ident">cdgh</span>.<span class="number">3</span>];
}</pre>
<p>instead of 4 rounds of:</p>
<pre class="rust rust-example-rendered">
<span class="kw">fn</span> <span class="ident">round</span>(<span class="ident">state</span>: <span class="kw-2">&amp;</span><span class="kw-2">mut</span> [<span class="ident">u32</span>; <span class="number">8</span>], <span class="ident">w</span>: <span class="kw-2">&amp;</span><span class="kw-2">mut</span> [<span class="ident">u32</span>], <span class="ident">t</span>: <span class="ident">usize</span>) {
<span class="kw">let</span> [<span class="ident">a</span>, <span class="ident">b</span>, <span class="ident">c</span>, <span class="kw-2">mut</span> <span class="ident">d</span>, <span class="ident">e</span>, <span class="ident">f</span>, <span class="ident">g</span>, <span class="kw-2">mut</span> <span class="ident">h</span>]: [<span class="ident">u32</span>; <span class="number">8</span>] <span class="op">=</span> <span class="kw-2">*</span><span class="ident">state</span>;
<span class="ident">h</span> <span class="op">+=</span> <span class="macro">big_sigma1</span><span class="macro">!</span>(<span class="ident">e</span>) <span class="op">+</span> <span class="macro">choose</span><span class="macro">!</span>(<span class="ident">e</span>, <span class="ident">f</span>, <span class="ident">g</span>) <span class="op">+</span> <span class="ident">K32</span>[<span class="ident">t</span>] <span class="op">+</span> <span class="ident">w</span>[<span class="ident">t</span>]; <span class="ident">d</span> <span class="op">+=</span> <span class="ident">h</span>;
<span class="ident">h</span> <span class="op">+=</span> <span class="macro">big_sigma0</span><span class="macro">!</span>(<span class="ident">a</span>) <span class="op">+</span> <span class="macro">majority</span><span class="macro">!</span>(<span class="ident">a</span>, <span class="ident">b</span>, <span class="ident">c</span>);
<span class="kw-2">*</span><span class="ident">state</span> <span class="op">=</span> [<span class="ident">h</span>, <span class="ident">a</span>, <span class="ident">b</span>, <span class="ident">c</span>, <span class="ident">d</span>, <span class="ident">e</span>, <span class="ident">f</span>, <span class="ident">g</span>];
}</pre>
<p><strong>NOTE</strong>: It is important to note, however, that these instructions are not implemented
by any CPU (at the time of this writing), and so they are emulated in this library
until the instructions become more common, and gain support in LLVM (and GCC, etc.).</p>
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