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Cryptographic Services</a> »</li> </ul> </div> <div class="document"> <div class="documentwrapper"> <div class="bodywrapper"> <div class="body"> <div class="section" id="module-hashlib"> <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."><tt class="xref py py-mod docutils literal"><span class="pre">hashlib</span></tt></a> — Secure hashes and message digests<a class="headerlink" href="#module-hashlib" title="Permalink to this headline">¶</a></h1> <p class="versionadded"> <span class="versionmodified">New in version 2.5.</span></p> <p id="index-0"><strong>Source code:</strong> <a class="reference external" href="http://hg.python.org/cpython/file/2.7/Lib/hashlib.py">Lib/hashlib.py</a></p> <hr class="docutils" /> <p>This module implements a common interface to many different secure hash and message digest algorithms. Included are the FIPS secure hash algorithms SHA1, SHA224, SHA256, SHA384, and SHA512 (defined in FIPS 180-2) as well as RSA’s MD5 algorithm (defined in Internet <span class="target" id="index-1"></span><a class="rfc reference external" href="http://tools.ietf.org/html/rfc1321.html"><strong>RFC 1321</strong></a>). The terms secure hash and message digest are interchangeable. Older algorithms were called message digests. The modern term is secure hash.</p> <div class="admonition note"> <p class="first admonition-title">Note</p> <p class="last">If you want the adler32 or crc32 hash functions they are available in the <a class="reference internal" href="zlib.html#module-zlib" title="zlib: Low-level interface to compression and decompression routines compatible with gzip."><tt class="xref py py-mod docutils literal"><span class="pre">zlib</span></tt></a> module.</p> </div> <div class="admonition warning"> <p class="first admonition-title">Warning</p> <p class="last">Some algorithms have known hash collision weaknesses, see the FAQ at the end.</p> </div> <p>There is one constructor method named for each type of <em class="dfn">hash</em>. All return a hash object with the same simple interface. For example: use <tt class="xref py py-func docutils literal"><span class="pre">sha1()</span></tt> to create a SHA1 hash object. You can now feed this object with arbitrary strings using the <tt class="xref py py-meth docutils literal"><span class="pre">update()</span></tt> method. At any point you can ask it for the <em class="dfn">digest</em> of the concatenation of the strings fed to it so far using the <tt class="xref py py-meth docutils literal"><span class="pre">digest()</span></tt> or <tt class="xref py py-meth docutils literal"><span class="pre">hexdigest()</span></tt> methods.</p> <p id="index-2">Constructors for hash algorithms that are always present in this module are <a class="reference internal" href="md5.html#module-md5" title="md5: RSA's MD5 message digest algorithm. (deprecated)"><tt class="xref py py-func docutils literal"><span class="pre">md5()</span></tt></a>, <tt class="xref py py-func docutils literal"><span class="pre">sha1()</span></tt>, <tt class="xref py py-func docutils literal"><span class="pre">sha224()</span></tt>, <tt class="xref py py-func docutils literal"><span class="pre">sha256()</span></tt>, <tt class="xref py py-func docutils literal"><span class="pre">sha384()</span></tt>, and <tt class="xref py py-func docutils literal"><span class="pre">sha512()</span></tt>. Additional algorithms may also be available depending upon the OpenSSL library that Python uses on your platform.</p> <p>For example, to obtain the digest of the string <tt class="docutils literal"><span class="pre">'Nobody</span> <span class="pre">inspects</span> <span class="pre">the</span> <span class="pre">spammish</span> <span class="pre">repetition'</span></tt>:</p> <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="kn">import</span> <span class="nn">hashlib</span> <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> <span class="gp">>>> </span><span class="n">m</span><span class="o">.</span><span class="n">update</span><span class="p">(</span><span class="s">"Nobody inspects"</span><span class="p">)</span> <span class="gp">>>> </span><span class="n">m</span><span class="o">.</span><span class="n">update</span><span class="p">(</span><span class="s">" the spammish repetition"</span><span class="p">)</span> <span class="gp">>>> </span><span class="n">m</span><span class="o">.</span><span class="n">digest</span><span class="p">()</span> <span class="go">'\xbbd\x9c\x83\xdd\x1e\xa5\xc9\xd9\xde\xc9\xa1\x8d\xf0\xff\xe9'</span> <span class="gp">>>> </span><span class="n">m</span><span class="o">.</span><span class="n">digest_size</span> <span class="go">16</span> <span class="gp">>>> </span><span class="n">m</span><span class="o">.</span><span class="n">block_size</span> <span class="go">64</span> </pre></div> </div> <p>More condensed:</p> <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">hashlib</span><span class="o">.</span><span class="n">sha224</span><span class="p">(</span><span class="s">"Nobody inspects the spammish repetition"</span><span class="p">)</span><span class="o">.</span><span class="n">hexdigest</span><span class="p">()</span> <span class="go">'a4337bc45a8fc544c03f52dc550cd6e1e87021bc896588bd79e901e2'</span> </pre></div> </div> <p>A generic <a class="reference internal" href="new.html#module-new" title="new: Interface to the creation of runtime implementation objects. (deprecated)"><tt class="xref py py-func docutils literal"><span class="pre">new()</span></tt></a> constructor that takes the string name of the desired algorithm as its first parameter also exists to allow access to the above listed hashes as well as any other algorithms that your OpenSSL library may offer. The 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)"><tt class="xref py py-func docutils literal"><span class="pre">new()</span></tt></a> and should be preferred.</p> <p>Using <a class="reference internal" href="new.html#module-new" title="new: Interface to the creation of runtime implementation objects. (deprecated)"><tt class="xref py py-func docutils literal"><span class="pre">new()</span></tt></a> with an algorithm provided by OpenSSL:</p> <div class="highlight-python"><div class="highlight"><pre><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="s">'ripemd160'</span><span class="p">)</span> <span class="gp">>>> </span><span class="n">h</span><span class="o">.</span><span class="n">update</span><span class="p">(</span><span class="s">"Nobody inspects the spammish repetition"</span><span class="p">)</span> <span class="gp">>>> </span><span class="n">h</span><span class="o">.</span><span class="n">hexdigest</span><span class="p">()</span> <span class="go">'cc4a5ce1b3df48aec5d22d1f16b894a0b894eccc'</span> </pre></div> </div> <p>This module provides the following constant attribute:</p> <dl class="data"> <dt id="hashlib.hashlib.algorithms"> <tt class="descclassname">hashlib.</tt><tt class="descname">algorithms</tt><a class="headerlink" href="#hashlib.hashlib.algorithms" title="Permalink to this definition">¶</a></dt> <dd><p>A tuple providing the names of the hash algorithms guaranteed to be supported by this module.</p> <p class="versionadded"> <span class="versionmodified">New in version 2.7.</span></p> </dd></dl> <p>The following values are provided as constant attributes of the hash objects returned by the constructors:</p> <dl class="data"> <dt id="hashlib.hash.digest_size"> <tt class="descclassname">hash.</tt><tt class="descname">digest_size</tt><a class="headerlink" href="#hashlib.hash.digest_size" title="Permalink to this definition">¶</a></dt> <dd><p>The size of the resulting hash in bytes.</p> </dd></dl> <dl class="data"> <dt id="hashlib.hash.block_size"> <tt class="descclassname">hash.</tt><tt class="descname">block_size</tt><a class="headerlink" href="#hashlib.hash.block_size" title="Permalink to this definition">¶</a></dt> <dd><p>The internal block size of the hash algorithm in bytes.</p> </dd></dl> <p>A hash object has the following methods:</p> <dl class="method"> <dt id="hashlib.hash.update"> <tt class="descclassname">hash.</tt><tt class="descname">update</tt><big>(</big><em>arg</em><big>)</big><a class="headerlink" href="#hashlib.hash.update" title="Permalink to this definition">¶</a></dt> <dd><p>Update the hash object with the string <em>arg</em>. Repeated calls are equivalent to a single call with the concatenation of all the arguments: <tt class="docutils literal"><span class="pre">m.update(a);</span> <span class="pre">m.update(b)</span></tt> is equivalent to <tt class="docutils literal"><span class="pre">m.update(a+b)</span></tt>.</p> <p class="versionchanged"> <span class="versionmodified">Changed in version 2.7.</span></p> </dd></dl> <dl class="method"> <dt id="hashlib.hash.digest"> <tt class="descclassname">hash.</tt><tt class="descname">digest</tt><big>(</big><big>)</big><a class="headerlink" href="#hashlib.hash.digest" title="Permalink to this definition">¶</a></dt> <dd><p>Return the digest of the strings passed to the <a class="reference internal" href="#hashlib.hash.update" title="hashlib.hash.update"><tt class="xref py py-meth docutils literal"><span class="pre">update()</span></tt></a> method so far. This is a string of <a class="reference internal" href="#hashlib.hash.digest_size" title="hashlib.hash.digest_size"><tt class="xref py py-attr docutils literal"><span class="pre">digest_size</span></tt></a> bytes which may contain non-ASCII characters, including null bytes.</p> </dd></dl> <dl class="method"> <dt id="hashlib.hash.hexdigest"> <tt class="descclassname">hash.</tt><tt class="descname">hexdigest</tt><big>(</big><big>)</big><a class="headerlink" href="#hashlib.hash.hexdigest" title="Permalink to this definition">¶</a></dt> <dd><p>Like <a class="reference internal" href="#hashlib.hash.digest" title="hashlib.hash.digest"><tt class="xref py py-meth docutils literal"><span class="pre">digest()</span></tt></a> except the digest is returned as a string of double length, containing only hexadecimal digits. This may be used to exchange the value safely in email or other non-binary environments.</p> </dd></dl> <dl class="method"> <dt id="hashlib.hash.copy"> <tt class="descclassname">hash.</tt><tt class="descname">copy</tt><big>(</big><big>)</big><a class="headerlink" href="#hashlib.hash.copy" title="Permalink to this definition">¶</a></dt> <dd><p>Return a copy (“clone”) of the hash object. This can be used to efficiently compute the digests of strings that share a common initial substring.</p> </dd></dl> <div class="admonition-see-also admonition seealso"> <p class="first admonition-title">See also</p> <dl class="last docutils"> <dt>Module <a class="reference internal" href="hmac.html#module-hmac" title="hmac: Keyed-Hashing for Message Authentication (HMAC) implementation for Python."><tt class="xref py py-mod docutils literal"><span class="pre">hmac</span></tt></a></dt> <dd>A module to generate message authentication codes using hashes.</dd> <dt>Module <a class="reference internal" href="base64.html#module-base64" title="base64: RFC 3548: Base16, Base32, Base64 Data Encodings"><tt class="xref py py-mod docutils literal"><span class="pre">base64</span></tt></a></dt> <dd>Another way to encode binary hashes for non-binary environments.</dd> <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> <dd>The FIPS 180-2 publication on Secure Hash Algorithms.</dd> <dt><a class="reference external" href="http://en.wikipedia.org/wiki/Cryptographic_hash_function#Cryptographic_hash_algorithms">http://en.wikipedia.org/wiki/Cryptographic_hash_function#Cryptographic_hash_algorithms</a></dt> <dd>Wikipedia article with information on which algorithms have known issues and what that means regarding their use.</dd> </dl> </div> </div> </div> </div> </div> <div class="sphinxsidebar"> <div class="sphinxsidebarwrapper"> <h4>Previous topic</h4> <p class="topless"><a href="crypto.html" title="previous chapter">14. 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