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<div class="example" id="sha1-hashes">
<h2><a href="./">Go by Example</a>: SHA1 Hashes</h2>
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<p><a href="http://en.wikipedia.org/wiki/SHA-1"><em>SHA1 hashes</em></a> are
frequently used to compute short identities for binary
or text blobs. For example, the <a href="http://git-scm.com/">git revision control
system</a> uses SHA1s extensively to
identify versioned files and directories. Here’s how to
compute SHA1 hashes in Go.</p>
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<a href="http://play.golang.org/p/YUaWWEeB4U"><img title="Run code" src="play.png" class="run" /></a>
<div class="highlight"><pre><span class="kn">package</span> <span class="nx">main</span>
</pre></div>
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<p>Go implements several hash functions in various
<code>crypto/*</code> packages.</p>
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<div class="highlight"><pre><span class="kn">import</span> <span class="s">"crypto/sha1"</span>
<span class="kn">import</span> <span class="s">"fmt"</span>
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<div class="highlight"><pre><span class="kd">func</span> <span class="nx">main</span><span class="p">()</span> <span class="p">{</span>
<span class="nx">s</span> <span class="o">:=</span> <span class="s">"sha1 this string"</span>
</pre></div>
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<p>The pattern for generating a hash is <code>sha1.New()</code>,
<code>sha1.Write(bytes)</code>, then <code>sha1.Sum([]byte{})</code>.
Here we start with a new hash.</p>
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<div class="highlight"><pre> <span class="nx">h</span> <span class="o">:=</span> <span class="nx">sha1</span><span class="p">.</span><span class="nx">New</span><span class="p">()</span>
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<p><code>Write</code> expects bytes. If you have a string <code>s</code>,
use <code>[]byte(s)</code> to coerce it to bytes.</p>
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<div class="highlight"><pre> <span class="nx">h</span><span class="p">.</span><span class="nx">Write</span><span class="p">([]</span><span class="nb">byte</span><span class="p">(</span><span class="nx">s</span><span class="p">))</span>
</pre></div>
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<p>This gets the finalized hash result as a byte
slice. The argument to <code>Sum</code> can be used to append
to an existing byte slice: it usually isn’t needed.</p>
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<div class="highlight"><pre> <span class="nx">bs</span> <span class="o">:=</span> <span class="nx">h</span><span class="p">.</span><span class="nx">Sum</span><span class="p">(</span><span class="kc">nil</span><span class="p">)</span>
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<p>SHA1 values are often printed in hex, for example
in git commits. Use the <code>%x</code> format verb to convert
a hash results to a hex string.</p>
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<div class="highlight"><pre> <span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="nx">s</span><span class="p">)</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nx">Printf</span><span class="p">(</span><span class="s">"%x\n"</span><span class="p">,</span> <span class="nx">bs</span><span class="p">)</span>
<span class="p">}</span>
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<p>Running the program computes the hash and prints it in
a human-readable hex format.</p>
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<div class="highlight"><pre><span class="gp">$</span> go run sha1-hashes.go
<span class="go">sha1 this string</span>
<span class="go">cf23df2207d99a74fbe169e3eba035e633b65d94</span>
</pre></div>
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<p>You can compute other hashes using a similar pattern to
the one shown above. For example, to compute MD5 hashes
import <code>crypto/md5</code> and use <code>md5.New()</code>.</p>
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<p>Note that if you need cryptographically secure hashes,
you should carefully research
<a href="http://en.wikipedia.org/wiki/Cryptographic_hash_function">hash strength</a>!</p>
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<p class="next">
Next example: <a href="base64-encoding">Base64 Encoding</a>.
</p>
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by <a href="https://twitter.com/mmcgrana">@mmcgrana</a> | <a href="mailto:mmcgrana@gmail.com">feedback</a> | <a href="https://github.com/mmcgrana/gobyexample/blob/master/examples/sha1-hashes">source</a> | <a href="https://github.com/mmcgrana/gobyexample#license">license</a>
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