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<div class="section" id="module-hashlib">
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<span id="hashlib-secure-hashes-and-message-digests"></span><h1>14.1. <a class="reference internal" href="#module-hashlib" title="hashlib: Secure hash and message digest algorithms."><code class="xref py py-mod docutils literal"><span class="pre">hashlib</span></code></a> — Secure hashes and message digests<a class="headerlink" href="#module-hashlib" title="Permalink to this headline">¶</a></h1>
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<div class="versionadded">
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<p><span class="versionmodified">New in version 2.5.</span></p>
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<p id="index-0"><strong>Source code:</strong> <a class="reference external" href="https://hg.python.org/cpython/file/2.7/Lib/hashlib.py">Lib/hashlib.py</a></p>
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<hr class="docutils" />
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<p>This module implements a common interface to many different secure hash and
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message digest algorithms. Included are the FIPS secure hash algorithms SHA1,
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SHA224, SHA256, SHA384, and SHA512 (defined in FIPS 180-2) as well as RSA’s MD5
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algorithm (defined in Internet <span class="target" id="index-1"></span><a class="rfc reference external" href="https://tools.ietf.org/html/rfc1321.html"><strong>RFC 1321</strong></a>). The terms secure hash and message
88
digest are interchangeable. Older algorithms were called message digests. The
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modern term is secure hash.</p>
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<div class="admonition note">
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<p class="first admonition-title">Note</p>
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<p class="last">If you want the adler32 or crc32 hash functions, they are available in
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the <a class="reference internal" href="zlib.html#module-zlib" title="zlib: Low-level interface to compression and decompression routines compatible with gzip."><code class="xref py py-mod docutils literal"><span class="pre">zlib</span></code></a> module.</p>
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<div class="admonition warning">
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<p class="first admonition-title">Warning</p>
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<p class="last">Some algorithms have known hash collision weaknesses, refer to the “See
98
also” section at the end.</p>
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<p>There is one constructor method named for each type of <em class="dfn">hash</em>. All return
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a hash object with the same simple interface. For example: use <code class="xref py py-func docutils literal"><span class="pre">sha1()</span></code> to
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create a SHA1 hash object. You can now feed this object with arbitrary strings
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using the <code class="xref py py-meth docutils literal"><span class="pre">update()</span></code> method. At any point you can ask it for the
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<em class="dfn">digest</em> of the concatenation of the strings fed to it so far using the
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<code class="xref py py-meth docutils literal"><span class="pre">digest()</span></code> or <code class="xref py py-meth docutils literal"><span class="pre">hexdigest()</span></code> methods.</p>
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<p id="index-2">Constructors for hash algorithms that are always present in this module are
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<a class="reference internal" href="md5.html#module-md5" title="md5: RSA's MD5 message digest algorithm. (deprecated)"><code class="xref py py-func docutils literal"><span class="pre">md5()</span></code></a>, <code class="xref py py-func docutils literal"><span class="pre">sha1()</span></code>, <code class="xref py py-func docutils literal"><span class="pre">sha224()</span></code>, <code class="xref py py-func docutils literal"><span class="pre">sha256()</span></code>, <code class="xref py py-func docutils literal"><span class="pre">sha384()</span></code>, and
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<code class="xref py py-func docutils literal"><span class="pre">sha512()</span></code>. Additional algorithms may also be available depending upon the
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OpenSSL library that Python uses on your platform.</p>
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<p>For example, to obtain the digest of the string <code class="docutils literal"><span class="pre">'Nobody</span> <span class="pre">inspects</span> <span class="pre">the</span> <span class="pre">spammish</span>
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<span class="pre">repetition'</span></code>:</p>
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<div class="highlight-python"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="kn">import</span> <span class="nn">hashlib</span>
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<span class="gp">>>> </span><span class="n">m</span> <span class="o">=</span> <span class="n">hashlib</span><span class="o">.</span><span class="n">md5</span><span class="p">()</span>
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<span class="gp">>>> </span><span class="n">m</span><span class="o">.</span><span class="n">update</span><span class="p">(</span><span class="s2">"Nobody inspects"</span><span class="p">)</span>
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<span class="gp">>>> </span><span class="n">m</span><span class="o">.</span><span class="n">update</span><span class="p">(</span><span class="s2">" the spammish repetition"</span><span class="p">)</span>
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<span class="gp">>>> </span><span class="n">m</span><span class="o">.</span><span class="n">digest</span><span class="p">()</span>
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<span class="go">'\xbbd\x9c\x83\xdd\x1e\xa5\xc9\xd9\xde\xc9\xa1\x8d\xf0\xff\xe9'</span>
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<span class="gp">>>> </span><span class="n">m</span><span class="o">.</span><span class="n">digest_size</span>
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<span class="go">16</span>
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<span class="gp">>>> </span><span class="n">m</span><span class="o">.</span><span class="n">block_size</span>
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<span class="go">64</span>
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<p>More condensed:</p>
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<div class="highlight-python"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">hashlib</span><span class="o">.</span><span class="n">sha224</span><span class="p">(</span><span class="s2">"Nobody inspects the spammish repetition"</span><span class="p">)</span><span class="o">.</span><span class="n">hexdigest</span><span class="p">()</span>
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<span class="go">'a4337bc45a8fc544c03f52dc550cd6e1e87021bc896588bd79e901e2'</span>
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<p>A generic <a class="reference internal" href="new.html#module-new" title="new: Interface to the creation of runtime implementation objects. (deprecated)"><code class="xref py py-func docutils literal"><span class="pre">new()</span></code></a> constructor that takes the string name of the desired
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algorithm as its first parameter also exists to allow access to the above listed
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hashes as well as any other algorithms that your OpenSSL library may offer. The
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named constructors are much faster than <a class="reference internal" href="new.html#module-new" title="new: Interface to the creation of runtime implementation objects. (deprecated)"><code class="xref py py-func docutils literal"><span class="pre">new()</span></code></a> and should be preferred.</p>
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<p>Using <a class="reference internal" href="new.html#module-new" title="new: Interface to the creation of runtime implementation objects. (deprecated)"><code class="xref py py-func docutils literal"><span class="pre">new()</span></code></a> with an algorithm provided by OpenSSL:</p>
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<div class="highlight-python"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">h</span> <span class="o">=</span> <span class="n">hashlib</span><span class="o">.</span><span class="n">new</span><span class="p">(</span><span class="s1">'ripemd160'</span><span class="p">)</span>
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<span class="gp">>>> </span><span class="n">h</span><span class="o">.</span><span class="n">update</span><span class="p">(</span><span class="s2">"Nobody inspects the spammish repetition"</span><span class="p">)</span>
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<span class="gp">>>> </span><span class="n">h</span><span class="o">.</span><span class="n">hexdigest</span><span class="p">()</span>
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<span class="go">'cc4a5ce1b3df48aec5d22d1f16b894a0b894eccc'</span>
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<p>This module provides the following constant attribute:</p>
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<dt id="hashlib.hashlib.algorithms">
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<code class="descclassname">hashlib.</code><code class="descname">algorithms</code><a class="headerlink" href="#hashlib.hashlib.algorithms" title="Permalink to this definition">¶</a></dt>
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<dd><p>A tuple providing the names of the hash algorithms guaranteed to be
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supported by this module.</p>
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<div class="versionadded">
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<p><span class="versionmodified">New in version 2.7.</span></p>
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<dt id="hashlib.algorithms_guaranteed">
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<code class="descclassname">hashlib.</code><code class="descname">algorithms_guaranteed</code><a class="headerlink" href="#hashlib.algorithms_guaranteed" title="Permalink to this definition">¶</a></dt>
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<dd><p>A set containing the names of the hash algorithms guaranteed to be supported
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by this module on all platforms.</p>
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<div class="versionadded">
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<p><span class="versionmodified">New in version 2.7.9.</span></p>
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<dt id="hashlib.algorithms_available">
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<code class="descclassname">hashlib.</code><code class="descname">algorithms_available</code><a class="headerlink" href="#hashlib.algorithms_available" title="Permalink to this definition">¶</a></dt>
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<dd><p>A set containing the names of the hash algorithms that are available in the
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running Python interpreter. These names will be recognized when passed to
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<a class="reference internal" href="new.html#module-new" title="new: Interface to the creation of runtime implementation objects. (deprecated)"><code class="xref py py-func docutils literal"><span class="pre">new()</span></code></a>. <a class="reference internal" href="#hashlib.algorithms_guaranteed" title="hashlib.algorithms_guaranteed"><code class="xref py py-attr docutils literal"><span class="pre">algorithms_guaranteed</span></code></a> will always be a subset. The
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same algorithm may appear multiple times in this set under different names
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(thanks to OpenSSL).</p>
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<div class="versionadded">
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<p><span class="versionmodified">New in version 2.7.9.</span></p>
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<p>The following values are provided as constant attributes of the hash objects
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returned by the constructors:</p>
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<dt id="hashlib.hash.digest_size">
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<code class="descclassname">hash.</code><code class="descname">digest_size</code><a class="headerlink" href="#hashlib.hash.digest_size" title="Permalink to this definition">¶</a></dt>
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<dd><p>The size of the resulting hash in bytes.</p>
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<dt id="hashlib.hash.block_size">
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<code class="descclassname">hash.</code><code class="descname">block_size</code><a class="headerlink" href="#hashlib.hash.block_size" title="Permalink to this definition">¶</a></dt>
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<dd><p>The internal block size of the hash algorithm in bytes.</p>
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<p>A hash object has the following methods:</p>
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<dt id="hashlib.hash.update">
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<code class="descclassname">hash.</code><code class="descname">update</code><span class="sig-paren">(</span><em>arg</em><span class="sig-paren">)</span><a class="headerlink" href="#hashlib.hash.update" title="Permalink to this definition">¶</a></dt>
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<dd><p>Update the hash object with the string <em>arg</em>. Repeated calls are equivalent to
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a single call with the concatenation of all the arguments: <code class="docutils literal"><span class="pre">m.update(a);</span>
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<span class="pre">m.update(b)</span></code> is equivalent to <code class="docutils literal"><span class="pre">m.update(a+b)</span></code>.</p>
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<div class="versionchanged">
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<p><span class="versionmodified">Changed in version 2.7: </span>The Python GIL is released to allow other threads to run while
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hash updates on data larger than 2048 bytes is taking place when
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using hash algorithms supplied by OpenSSL.</p>
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<dt id="hashlib.hash.digest">
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<code class="descclassname">hash.</code><code class="descname">digest</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#hashlib.hash.digest" title="Permalink to this definition">¶</a></dt>
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<dd><p>Return the digest of the strings passed to the <a class="reference internal" href="#hashlib.hash.update" title="hashlib.hash.update"><code class="xref py py-meth docutils literal"><span class="pre">update()</span></code></a> method so far.
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This is a string of <a class="reference internal" href="#hashlib.hash.digest_size" title="hashlib.hash.digest_size"><code class="xref py py-attr docutils literal"><span class="pre">digest_size</span></code></a> bytes which may contain non-ASCII
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characters, including null bytes.</p>
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<dt id="hashlib.hash.hexdigest">
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<code class="descclassname">hash.</code><code class="descname">hexdigest</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#hashlib.hash.hexdigest" title="Permalink to this definition">¶</a></dt>
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<dd><p>Like <a class="reference internal" href="#hashlib.hash.digest" title="hashlib.hash.digest"><code class="xref py py-meth docutils literal"><span class="pre">digest()</span></code></a> except the digest is returned as a string of double length,
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containing only hexadecimal digits. This may be used to exchange the value
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safely in email or other non-binary environments.</p>
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<dt id="hashlib.hash.copy">
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<code class="descclassname">hash.</code><code class="descname">copy</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#hashlib.hash.copy" title="Permalink to this definition">¶</a></dt>
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<dd><p>Return a copy (“clone”) of the hash object. This can be used to efficiently
222
compute the digests of strings that share a common initial substring.</p>
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<div class="section" id="key-derivation">
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<h2>14.1.1. Key derivation<a class="headerlink" href="#key-derivation" title="Permalink to this headline">¶</a></h2>
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<p>Key derivation and key stretching algorithms are designed for secure password
228
hashing. Naive algorithms such as <code class="docutils literal"><span class="pre">sha1(password)</span></code> are not resistant against
229
brute-force attacks. A good password hashing function must be tunable, slow, and
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include a <a class="reference external" href="https://en.wikipedia.org/wiki/Salt_%28cryptography%29">salt</a>.</p>
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<dl class="function">
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<dt id="hashlib.pbkdf2_hmac">
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<code class="descclassname">hashlib.</code><code class="descname">pbkdf2_hmac</code><span class="sig-paren">(</span><em>name</em>, <em>password</em>, <em>salt</em>, <em>rounds</em>, <em>dklen=None</em><span class="sig-paren">)</span><a class="headerlink" href="#hashlib.pbkdf2_hmac" title="Permalink to this definition">¶</a></dt>
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<dd><p>The function provides PKCS#5 password-based key derivation function 2. It
235
uses HMAC as pseudorandom function.</p>
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<p>The string <em>name</em> is the desired name of the hash digest algorithm for
237
HMAC, e.g. ‘sha1’ or ‘sha256’. <em>password</em> and <em>salt</em> are interpreted as
238
buffers of bytes. Applications and libraries should limit <em>password</em> to
239
a sensible value (e.g. 1024). <em>salt</em> should be about 16 or more bytes from
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a proper source, e.g. <a class="reference internal" href="os.html#os.urandom" title="os.urandom"><code class="xref py py-func docutils literal"><span class="pre">os.urandom()</span></code></a>.</p>
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<p>The number of <em>rounds</em> should be chosen based on the hash algorithm and
242
computing power. As of 2013, at least 100,000 rounds of SHA-256 is suggested.</p>
243
<p><em>dklen</em> is the length of the derived key. If <em>dklen</em> is <code class="docutils literal"><span class="pre">None</span></code> then the
244
digest size of the hash algorithm <em>name</em> is used, e.g. 64 for SHA-512.</p>
245
<div class="highlight-python"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="kn">import</span> <span class="nn">hashlib</span><span class="o">,</span> <span class="nn">binascii</span>
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<span class="gp">>>> </span><span class="n">dk</span> <span class="o">=</span> <span class="n">hashlib</span><span class="o">.</span><span class="n">pbkdf2_hmac</span><span class="p">(</span><span class="s1">'sha256'</span><span class="p">,</span> <span class="n">b</span><span class="s1">'password'</span><span class="p">,</span> <span class="n">b</span><span class="s1">'salt'</span><span class="p">,</span> <span class="mi">100000</span><span class="p">)</span>
247
<span class="gp">>>> </span><span class="n">binascii</span><span class="o">.</span><span class="n">hexlify</span><span class="p">(</span><span class="n">dk</span><span class="p">)</span>
248
<span class="go">b'0394a2ede332c9a13eb82e9b24631604c31df978b4e2f0fbd2c549944f9d79a5'</span>
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<div class="versionadded">
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<p><span class="versionmodified">New in version 2.7.8.</span></p>
254
<div class="admonition note">
255
<p class="first admonition-title">Note</p>
256
<p class="last">A fast implementation of <em>pbkdf2_hmac</em> is available with OpenSSL. The
257
Python implementation uses an inline version of <a class="reference internal" href="hmac.html#module-hmac" title="hmac: Keyed-Hashing for Message Authentication (HMAC) implementation"><code class="xref py py-mod docutils literal"><span class="pre">hmac</span></code></a>. It is about
258
three times slower and doesn’t release the GIL.</p>
262
<div class="admonition seealso">
263
<p class="first admonition-title">See also</p>
264
<dl class="last docutils">
265
<dt>Module <a class="reference internal" href="hmac.html#module-hmac" title="hmac: Keyed-Hashing for Message Authentication (HMAC) implementation"><code class="xref py py-mod docutils literal"><span class="pre">hmac</span></code></a></dt>
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<dd>A module to generate message authentication codes using hashes.</dd>
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<dt>Module <a class="reference internal" href="base64.html#module-base64" title="base64: RFC 3548: Base16, Base32, Base64 Data Encodings"><code class="xref py py-mod docutils literal"><span class="pre">base64</span></code></a></dt>
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<dd>Another way to encode binary hashes for non-binary environments.</dd>
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<dt><a class="reference external" href="http://csrc.nist.gov/publications/fips/fips180-2/fips180-2.pdf">http://csrc.nist.gov/publications/fips/fips180-2/fips180-2.pdf</a></dt>
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<dd>The FIPS 180-2 publication on Secure Hash Algorithms.</dd>
271
<dt><a class="reference external" href="https://en.wikipedia.org/wiki/Cryptographic_hash_function#Cryptographic_hash_algorithms">https://en.wikipedia.org/wiki/Cryptographic_hash_function#Cryptographic_hash_algorithms</a></dt>
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<dd>Wikipedia article with information on which algorithms have known issues and
273
what that means regarding their use.</dd>
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<h3><a href="../contents.html">Table Of Contents</a></h3>
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<li><a class="reference internal" href="#">14.1. <code class="docutils literal"><span class="pre">hashlib</span></code> — Secure hashes and message digests</a><ul>
288
<li><a class="reference internal" href="#key-derivation">14.1.1. Key derivation</a></li>
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python-2.7.12-docs-html/library/hashlib.html
