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<title>hashlib — Secure hashes and message digests &#8212; Python 3.7.4 documentation</title>
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<div class="section" id="module-hashlib">
<span id="hashlib-secure-hashes-and-message-digests"></span><h1><a class="reference internal" href="#module-hashlib" title="hashlib: Secure hash and message digest algorithms."><code class="xref py py-mod docutils literal notranslate"><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>
<p><strong>Source code:</strong> <a class="reference external" href="https://github.com/python/cpython/tree/3.7/Lib/hashlib.py">Lib/hashlib.py</a></p>
<span class="target" id="index-0"></span><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="https://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="admonition-title">Note</p>
<p>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."><code class="xref py py-mod docutils literal notranslate"><span class="pre">zlib</span></code></a> module.</p>
</div>
<div class="admonition warning">
<p class="admonition-title">Warning</p>
<p>Some algorithms have known hash collision weaknesses, refer to the “See
also” section at the end.</p>
</div>
<div class="section" id="hash-algorithms">
<span id="id1"></span><h2>Hash algorithms<a class="headerlink" href="#hash-algorithms" title="Permalink to this headline"></a></h2>
<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 <code class="xref py py-func docutils literal notranslate"><span class="pre">sha256()</span></code> to
create a SHA-256 hash object. You can now feed this object with <a class="reference internal" href="../glossary.html#term-bytes-like-object"><span class="xref std std-term">bytes-like
objects</span></a> (normally <a class="reference internal" href="stdtypes.html#bytes" title="bytes"><code class="xref py py-class docutils literal notranslate"><span class="pre">bytes</span></code></a>) using the <code class="xref py py-meth docutils literal notranslate"><span class="pre">update()</span></code> method.
At any point you can ask it for the <em class="dfn">digest</em> of the
concatenation of the data fed to it so far using the <code class="xref py py-meth docutils literal notranslate"><span class="pre">digest()</span></code> or
<code class="xref py py-meth docutils literal notranslate"><span class="pre">hexdigest()</span></code> methods.</p>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>For better multithreading performance, the Python <a class="reference internal" href="../glossary.html#term-gil"><span class="xref std std-term">GIL</span></a> is released for
data larger than 2047 bytes at object creation or on update.</p>
</div>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>Feeding string objects into <code class="xref py py-meth docutils literal notranslate"><span class="pre">update()</span></code> is not supported, as hashes work
on bytes, not on characters.</p>
</div>
<p id="index-2">Constructors for hash algorithms that are always present in this module are
<code class="xref py py-func docutils literal notranslate"><span class="pre">sha1()</span></code>, <code class="xref py py-func docutils literal notranslate"><span class="pre">sha224()</span></code>, <code class="xref py py-func docutils literal notranslate"><span class="pre">sha256()</span></code>, <code class="xref py py-func docutils literal notranslate"><span class="pre">sha384()</span></code>,
<code class="xref py py-func docutils literal notranslate"><span class="pre">sha512()</span></code>, <a class="reference internal" href="#hashlib.blake2b" title="hashlib.blake2b"><code class="xref py py-func docutils literal notranslate"><span class="pre">blake2b()</span></code></a>, and <a class="reference internal" href="#hashlib.blake2s" title="hashlib.blake2s"><code class="xref py py-func docutils literal notranslate"><span class="pre">blake2s()</span></code></a>.
<code class="xref py py-func docutils literal notranslate"><span class="pre">md5()</span></code> is normally available as well, though it
may be missing if you are using a rare “FIPS compliant” build of Python.
Additional algorithms may also be available depending upon the OpenSSL
library that Python uses on your platform. On most platforms the
<code class="xref py py-func docutils literal notranslate"><span class="pre">sha3_224()</span></code>, <code class="xref py py-func docutils literal notranslate"><span class="pre">sha3_256()</span></code>, <code class="xref py py-func docutils literal notranslate"><span class="pre">sha3_384()</span></code>, <code class="xref py py-func docutils literal notranslate"><span class="pre">sha3_512()</span></code>,
<code class="xref py py-func docutils literal notranslate"><span class="pre">shake_128()</span></code>, <code class="xref py py-func docutils literal notranslate"><span class="pre">shake_256()</span></code> are also available.</p>
<div class="versionadded">
<p><span class="versionmodified added">New in version 3.6: </span>SHA3 (Keccak) and SHAKE constructors <code class="xref py py-func docutils literal notranslate"><span class="pre">sha3_224()</span></code>, <code class="xref py py-func docutils literal notranslate"><span class="pre">sha3_256()</span></code>,
<code class="xref py py-func docutils literal notranslate"><span class="pre">sha3_384()</span></code>, <code class="xref py py-func docutils literal notranslate"><span class="pre">sha3_512()</span></code>, <code class="xref py py-func docutils literal notranslate"><span class="pre">shake_128()</span></code>, <code class="xref py py-func docutils literal notranslate"><span class="pre">shake_256()</span></code>.</p>
</div>
<div class="versionadded">
<p><span class="versionmodified added">New in version 3.6: </span><a class="reference internal" href="#hashlib.blake2b" title="hashlib.blake2b"><code class="xref py py-func docutils literal notranslate"><span class="pre">blake2b()</span></code></a> and <a class="reference internal" href="#hashlib.blake2s" title="hashlib.blake2s"><code class="xref py py-func docutils literal notranslate"><span class="pre">blake2s()</span></code></a> were added.</p>
</div>
<p>For example, to obtain the digest of the byte string <code class="docutils literal notranslate"><span class="pre">b'Nobody</span> <span class="pre">inspects</span> <span class="pre">the</span>
<span class="pre">spammish</span> <span class="pre">repetition'</span></code>:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="kn">import</span> <span class="nn">hashlib</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">m</span> <span class="o">=</span> <span class="n">hashlib</span><span class="o">.</span><span class="n">sha256</span><span class="p">()</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">m</span><span class="o">.</span><span class="n">update</span><span class="p">(</span><span class="sa">b</span><span class="s2">&quot;Nobody inspects&quot;</span><span class="p">)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">m</span><span class="o">.</span><span class="n">update</span><span class="p">(</span><span class="sa">b</span><span class="s2">&quot; the spammish repetition&quot;</span><span class="p">)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">m</span><span class="o">.</span><span class="n">digest</span><span class="p">()</span>
<span class="go">b&#39;\x03\x1e\xdd}Ae\x15\x93\xc5\xfe\\\x00o\xa5u+7\xfd\xdf\xf7\xbcN\x84:\xa6\xaf\x0c\x95\x0fK\x94\x06&#39;</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">m</span><span class="o">.</span><span class="n">digest_size</span>
<span class="go">32</span>
<span class="gp">&gt;&gt;&gt; </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-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">hashlib</span><span class="o">.</span><span class="n">sha224</span><span class="p">(</span><span class="sa">b</span><span class="s2">&quot;Nobody inspects the spammish repetition&quot;</span><span class="p">)</span><span class="o">.</span><span class="n">hexdigest</span><span class="p">()</span>
<span class="go">&#39;a4337bc45a8fc544c03f52dc550cd6e1e87021bc896588bd79e901e2&#39;</span>
</pre></div>
</div>
<dl class="function">
<dt id="hashlib.new">
<code class="descclassname">hashlib.</code><code class="descname">new</code><span class="sig-paren">(</span><em>name</em><span class="optional">[</span>, <em>data</em><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#hashlib.new" title="Permalink to this definition"></a></dt>
<dd><p>Is a generic constructor that takes the string <em>name</em> of the desired
algorithm as its first parameter. It 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="#hashlib.new" title="hashlib.new"><code class="xref py py-func docutils literal notranslate"><span class="pre">new()</span></code></a>
and should be preferred.</p>
</dd></dl>
<p>Using <a class="reference internal" href="#hashlib.new" title="hashlib.new"><code class="xref py py-func docutils literal notranslate"><span class="pre">new()</span></code></a> with an algorithm provided by OpenSSL:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </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">&#39;ripemd160&#39;</span><span class="p">)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">h</span><span class="o">.</span><span class="n">update</span><span class="p">(</span><span class="sa">b</span><span class="s2">&quot;Nobody inspects the spammish repetition&quot;</span><span class="p">)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">h</span><span class="o">.</span><span class="n">hexdigest</span><span class="p">()</span>
<span class="go">&#39;cc4a5ce1b3df48aec5d22d1f16b894a0b894eccc&#39;</span>
</pre></div>
</div>
<p>Hashlib provides the following constant attributes:</p>
<dl class="data">
<dt id="hashlib.algorithms_guaranteed">
<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>
<dd><p>A set containing the names of the hash algorithms guaranteed to be supported
by this module on all platforms. Note that ‘md5’ is in this list despite
some upstream vendors offering an odd “FIPS compliant” Python build that
excludes it.</p>
<div class="versionadded">
<p><span class="versionmodified added">New in version 3.2.</span></p>
</div>
</dd></dl>
<dl class="data">
<dt id="hashlib.algorithms_available">
<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>
<dd><p>A set containing the names of the hash algorithms that are available in the
running Python interpreter. These names will be recognized when passed to
<a class="reference internal" href="#hashlib.new" title="hashlib.new"><code class="xref py py-func docutils literal notranslate"><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 notranslate"><span class="pre">algorithms_guaranteed</span></code></a> will always be a subset. The
same algorithm may appear multiple times in this set under different names
(thanks to OpenSSL).</p>
<div class="versionadded">
<p><span class="versionmodified added">New in version 3.2.</span></p>
</div>
</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">
<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>
<dd><p>The size of the resulting hash in bytes.</p>
</dd></dl>
<dl class="data">
<dt id="hashlib.hash.block_size">
<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>
<dd><p>The internal block size of the hash algorithm in bytes.</p>
</dd></dl>
<p>A hash object has the following attributes:</p>
<dl class="attribute">
<dt id="hashlib.hash.name">
<code class="descclassname">hash.</code><code class="descname">name</code><a class="headerlink" href="#hashlib.hash.name" title="Permalink to this definition"></a></dt>
<dd><p>The canonical name of this hash, always lowercase and always suitable as a
parameter to <a class="reference internal" href="#hashlib.new" title="hashlib.new"><code class="xref py py-func docutils literal notranslate"><span class="pre">new()</span></code></a> to create another hash of this type.</p>
<div class="versionchanged">
<p><span class="versionmodified changed">Changed in version 3.4: </span>The name attribute has been present in CPython since its inception, but
until Python 3.4 was not formally specified, so may not exist on some
platforms.</p>
</div>
</dd></dl>
<p>A hash object has the following methods:</p>
<dl class="method">
<dt id="hashlib.hash.update">
<code class="descclassname">hash.</code><code class="descname">update</code><span class="sig-paren">(</span><em>data</em><span class="sig-paren">)</span><a class="headerlink" href="#hashlib.hash.update" title="Permalink to this definition"></a></dt>
<dd><p>Update the hash object with the <a class="reference internal" href="../glossary.html#term-bytes-like-object"><span class="xref std std-term">bytes-like object</span></a>.
Repeated calls are equivalent to a single call with the
concatenation of all the arguments: <code class="docutils literal notranslate"><span class="pre">m.update(a);</span> <span class="pre">m.update(b)</span></code> is
equivalent to <code class="docutils literal notranslate"><span class="pre">m.update(a+b)</span></code>.</p>
<div class="versionchanged">
<p><span class="versionmodified changed">Changed in version 3.1: </span>The Python GIL is released to allow other threads to run while hash
updates on data larger than 2047 bytes is taking place when using hash
algorithms supplied by OpenSSL.</p>
</div>
</dd></dl>
<dl class="method">
<dt id="hashlib.hash.digest">
<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>
<dd><p>Return the digest of the data passed to the <a class="reference internal" href="#hashlib.hash.update" title="hashlib.hash.update"><code class="xref py py-meth docutils literal notranslate"><span class="pre">update()</span></code></a> method so far.
This is a bytes object of size <a class="reference internal" href="#hashlib.hash.digest_size" title="hashlib.hash.digest_size"><code class="xref py py-attr docutils literal notranslate"><span class="pre">digest_size</span></code></a> which may contain bytes in
the whole range from 0 to 255.</p>
</dd></dl>
<dl class="method">
<dt id="hashlib.hash.hexdigest">
<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>
<dd><p>Like <a class="reference internal" href="#hashlib.hash.digest" title="hashlib.hash.digest"><code class="xref py py-meth docutils literal notranslate"><span class="pre">digest()</span></code></a> except the digest is returned as a string object 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">
<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>
<dd><p>Return a copy (“clone”) of the hash object. This can be used to efficiently
compute the digests of data sharing a common initial substring.</p>
</dd></dl>
</div>
<div class="section" id="shake-variable-length-digests">
<h2>SHAKE variable length digests<a class="headerlink" href="#shake-variable-length-digests" title="Permalink to this headline"></a></h2>
<p>The <code class="xref py py-func docutils literal notranslate"><span class="pre">shake_128()</span></code> and <code class="xref py py-func docutils literal notranslate"><span class="pre">shake_256()</span></code> algorithms provide variable
length digests with length_in_bits//2 up to 128 or 256 bits of security.
As such, their digest methods require a length. Maximum length is not limited
by the SHAKE algorithm.</p>
<dl class="method">
<dt id="hashlib.shake.digest">
<code class="descclassname">shake.</code><code class="descname">digest</code><span class="sig-paren">(</span><em>length</em><span class="sig-paren">)</span><a class="headerlink" href="#hashlib.shake.digest" title="Permalink to this definition"></a></dt>
<dd><p>Return the digest of the data passed to the <code class="xref py py-meth docutils literal notranslate"><span class="pre">update()</span></code> method so far.
This is a bytes object of size <em>length</em> which may contain bytes in
the whole range from 0 to 255.</p>
</dd></dl>
<dl class="method">
<dt id="hashlib.shake.hexdigest">
<code class="descclassname">shake.</code><code class="descname">hexdigest</code><span class="sig-paren">(</span><em>length</em><span class="sig-paren">)</span><a class="headerlink" href="#hashlib.shake.hexdigest" title="Permalink to this definition"></a></dt>
<dd><p>Like <a class="reference internal" href="#hashlib.shake.digest" title="hashlib.shake.digest"><code class="xref py py-meth docutils literal notranslate"><span class="pre">digest()</span></code></a> except the digest is returned as a string object 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>
</div>
<div class="section" id="key-derivation">
<h2>Key derivation<a class="headerlink" href="#key-derivation" title="Permalink to this headline"></a></h2>
<p>Key derivation and key stretching algorithms are designed for secure password
hashing. Naive algorithms such as <code class="docutils literal notranslate"><span class="pre">sha1(password)</span></code> are not resistant against
brute-force attacks. A good password hashing function must be tunable, slow, and
include a <a class="reference external" href="https://en.wikipedia.org/wiki/Salt_%28cryptography%29">salt</a>.</p>
<dl class="function">
<dt id="hashlib.pbkdf2_hmac">
<code class="descclassname">hashlib.</code><code class="descname">pbkdf2_hmac</code><span class="sig-paren">(</span><em>hash_name</em>, <em>password</em>, <em>salt</em>, <em>iterations</em>, <em>dklen=None</em><span class="sig-paren">)</span><a class="headerlink" href="#hashlib.pbkdf2_hmac" title="Permalink to this definition"></a></dt>
<dd><p>The function provides PKCS#5 password-based key derivation function 2. It
uses HMAC as pseudorandom function.</p>
<p>The string <em>hash_name</em> is the desired name of the hash digest algorithm for
HMAC, e.g. ‘sha1’ or ‘sha256’. <em>password</em> and <em>salt</em> are interpreted as
buffers of bytes. Applications and libraries should limit <em>password</em> to
a sensible length (e.g. 1024). <em>salt</em> should be about 16 or more bytes from
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 notranslate"><span class="pre">os.urandom()</span></code></a>.</p>
<p>The number of <em>iterations</em> should be chosen based on the hash algorithm and
computing power. As of 2013, at least 100,000 iterations of SHA-256 are
suggested.</p>
<p><em>dklen</em> is the length of the derived key. If <em>dklen</em> is <code class="docutils literal notranslate"><span class="pre">None</span></code> then the
digest size of the hash algorithm <em>hash_name</em> is used, e.g. 64 for SHA-512.</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="kn">import</span> <span class="nn">hashlib</span><span class="o">,</span> <span class="nn">binascii</span>
<span class="gp">&gt;&gt;&gt; </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">&#39;sha256&#39;</span><span class="p">,</span> <span class="sa">b</span><span class="s1">&#39;password&#39;</span><span class="p">,</span> <span class="sa">b</span><span class="s1">&#39;salt&#39;</span><span class="p">,</span> <span class="mi">100000</span><span class="p">)</span>
<span class="gp">&gt;&gt;&gt; </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>
<span class="go">b&#39;0394a2ede332c9a13eb82e9b24631604c31df978b4e2f0fbd2c549944f9d79a5&#39;</span>
</pre></div>
</div>
<div class="versionadded">
<p><span class="versionmodified added">New in version 3.4.</span></p>
</div>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>A fast implementation of <em>pbkdf2_hmac</em> is available with OpenSSL. The
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 notranslate"><span class="pre">hmac</span></code></a>. It is about
three times slower and doesn’t release the GIL.</p>
</div>
</dd></dl>
<dl class="function">
<dt id="hashlib.scrypt">
<code class="descclassname">hashlib.</code><code class="descname">scrypt</code><span class="sig-paren">(</span><em>password</em>, <em>*</em>, <em>salt</em>, <em>n</em>, <em>r</em>, <em>p</em>, <em>maxmem=0</em>, <em>dklen=64</em><span class="sig-paren">)</span><a class="headerlink" href="#hashlib.scrypt" title="Permalink to this definition"></a></dt>
<dd><p>The function provides scrypt password-based key derivation function as
defined in <span class="target" id="index-3"></span><a class="rfc reference external" href="https://tools.ietf.org/html/rfc7914.html"><strong>RFC 7914</strong></a>.</p>
<p><em>password</em> and <em>salt</em> must be <a class="reference internal" href="../glossary.html#term-bytes-like-object"><span class="xref std std-term">bytes-like objects</span></a>. Applications and libraries should limit <em>password</em>
to a sensible length (e.g. 1024). <em>salt</em> should be about 16 or more
bytes from 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 notranslate"><span class="pre">os.urandom()</span></code></a>.</p>
<p><em>n</em> is the CPU/Memory cost factor, <em>r</em> the block size, <em>p</em> parallelization
factor and <em>maxmem</em> limits memory (OpenSSL 1.1.0 defaults to 32 MiB).
<em>dklen</em> is the length of the derived key.</p>
<p class="availability"><a class="reference internal" href="intro.html#availability"><span class="std std-ref">Availability</span></a>: OpenSSL 1.1+.</p>
<div class="versionadded">
<p><span class="versionmodified added">New in version 3.6.</span></p>
</div>
</dd></dl>
</div>
<div class="section" id="blake2">
<h2>BLAKE2<a class="headerlink" href="#blake2" title="Permalink to this headline"></a></h2>
<p id="index-4"><a class="reference external" href="https://blake2.net">BLAKE2</a> is a cryptographic hash function defined in <span class="target" id="index-5"></span><a class="rfc reference external" href="https://tools.ietf.org/html/rfc7693.html"><strong>RFC 7693</strong></a> that comes in two
flavors:</p>
<ul class="simple">
<li><p><strong>BLAKE2b</strong>, optimized for 64-bit platforms and produces digests of any size
between 1 and 64 bytes,</p></li>
<li><p><strong>BLAKE2s</strong>, optimized for 8- to 32-bit platforms and produces digests of any
size between 1 and 32 bytes.</p></li>
</ul>
<p>BLAKE2 supports <strong>keyed mode</strong> (a faster and simpler replacement for <a class="reference external" href="https://en.wikipedia.org/wiki/Hash-based_message_authentication_code">HMAC</a>),
<strong>salted hashing</strong>, <strong>personalization</strong>, and <strong>tree hashing</strong>.</p>
<p>Hash objects from this module follow the API of standard library’s
<a class="reference internal" href="#module-hashlib" title="hashlib: Secure hash and message digest algorithms."><code class="xref py py-mod docutils literal notranslate"><span class="pre">hashlib</span></code></a> objects.</p>
<div class="section" id="creating-hash-objects">
<h3>Creating hash objects<a class="headerlink" href="#creating-hash-objects" title="Permalink to this headline"></a></h3>
<p>New hash objects are created by calling constructor functions:</p>
<dl class="function">
<dt id="hashlib.blake2b">
<code class="descclassname">hashlib.</code><code class="descname">blake2b</code><span class="sig-paren">(</span><em>data=b''</em>, <em>*</em>, <em>digest_size=64</em>, <em>key=b''</em>, <em>salt=b''</em>, <em>person=b''</em>, <em>fanout=1</em>, <em>depth=1</em>, <em>leaf_size=0</em>, <em>node_offset=0</em>, <em>node_depth=0</em>, <em>inner_size=0</em>, <em>last_node=False</em><span class="sig-paren">)</span><a class="headerlink" href="#hashlib.blake2b" title="Permalink to this definition"></a></dt>
<dd></dd></dl>
<dl class="function">
<dt id="hashlib.blake2s">
<code class="descclassname">hashlib.</code><code class="descname">blake2s</code><span class="sig-paren">(</span><em>data=b''</em>, <em>*</em>, <em>digest_size=32</em>, <em>key=b''</em>, <em>salt=b''</em>, <em>person=b''</em>, <em>fanout=1</em>, <em>depth=1</em>, <em>leaf_size=0</em>, <em>node_offset=0</em>, <em>node_depth=0</em>, <em>inner_size=0</em>, <em>last_node=False</em><span class="sig-paren">)</span><a class="headerlink" href="#hashlib.blake2s" title="Permalink to this definition"></a></dt>
<dd></dd></dl>
<p>These functions return the corresponding hash objects for calculating
BLAKE2b or BLAKE2s. They optionally take these general parameters:</p>
<ul class="simple">
<li><p><em>data</em>: initial chunk of data to hash, which must be
<a class="reference internal" href="../glossary.html#term-bytes-like-object"><span class="xref std std-term">bytes-like object</span></a>. It can be passed only as positional argument.</p></li>
<li><p><em>digest_size</em>: size of output digest in bytes.</p></li>
<li><p><em>key</em>: key for keyed hashing (up to 64 bytes for BLAKE2b, up to 32 bytes for
BLAKE2s).</p></li>
<li><p><em>salt</em>: salt for randomized hashing (up to 16 bytes for BLAKE2b, up to 8
bytes for BLAKE2s).</p></li>
<li><p><em>person</em>: personalization string (up to 16 bytes for BLAKE2b, up to 8 bytes
for BLAKE2s).</p></li>
</ul>
<p>The following table shows limits for general parameters (in bytes):</p>
<table class="docutils align-center">
<colgroup>
<col style="width: 15%" />
<col style="width: 24%" />
<col style="width: 17%" />
<col style="width: 20%" />
<col style="width: 24%" />
</colgroup>
<thead>
<tr class="row-odd"><th class="head"><p>Hash</p></th>
<th class="head"><p>digest_size</p></th>
<th class="head"><p>len(key)</p></th>
<th class="head"><p>len(salt)</p></th>
<th class="head"><p>len(person)</p></th>
</tr>
</thead>
<tbody>
<tr class="row-even"><td><p>BLAKE2b</p></td>
<td><p>64</p></td>
<td><p>64</p></td>
<td><p>16</p></td>
<td><p>16</p></td>
</tr>
<tr class="row-odd"><td><p>BLAKE2s</p></td>
<td><p>32</p></td>
<td><p>32</p></td>
<td><p>8</p></td>
<td><p>8</p></td>
</tr>
</tbody>
</table>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>BLAKE2 specification defines constant lengths for salt and personalization
parameters, however, for convenience, this implementation accepts byte
strings of any size up to the specified length. If the length of the
parameter is less than specified, it is padded with zeros, thus, for
example, <code class="docutils literal notranslate"><span class="pre">b'salt'</span></code> and <code class="docutils literal notranslate"><span class="pre">b'salt\x00'</span></code> is the same value. (This is not
the case for <em>key</em>.)</p>
</div>
<p>These sizes are available as module <a class="reference internal" href="#constants">constants</a> described below.</p>
<p>Constructor functions also accept the following tree hashing parameters:</p>
<ul class="simple">
<li><p><em>fanout</em>: fanout (0 to 255, 0 if unlimited, 1 in sequential mode).</p></li>
<li><p><em>depth</em>: maximal depth of tree (1 to 255, 255 if unlimited, 1 in
sequential mode).</p></li>
<li><p><em>leaf_size</em>: maximal byte length of leaf (0 to 2**32-1, 0 if unlimited or in
sequential mode).</p></li>
<li><p><em>node_offset</em>: node offset (0 to 2**64-1 for BLAKE2b, 0 to 2**48-1 for
BLAKE2s, 0 for the first, leftmost, leaf, or in sequential mode).</p></li>
<li><p><em>node_depth</em>: node depth (0 to 255, 0 for leaves, or in sequential mode).</p></li>
<li><p><em>inner_size</em>: inner digest size (0 to 64 for BLAKE2b, 0 to 32 for
BLAKE2s, 0 in sequential mode).</p></li>
<li><p><em>last_node</em>: boolean indicating whether the processed node is the last
one (<cite>False</cite> for sequential mode).</p></li>
</ul>
<div class="figure align-center">
<img alt="Explanation of tree mode parameters." src="../_images/hashlib-blake2-tree.png" />
</div>
<p>See section 2.10 in <a class="reference external" href="https://blake2.net/blake2_20130129.pdf">BLAKE2 specification</a> for comprehensive review of tree
hashing.</p>
</div>
<div class="section" id="constants">
<h3>Constants<a class="headerlink" href="#constants" title="Permalink to this headline"></a></h3>
<dl class="data">
<dt id="hashlib.blake2b.SALT_SIZE">
<code class="descclassname">blake2b.</code><code class="descname">SALT_SIZE</code><a class="headerlink" href="#hashlib.blake2b.SALT_SIZE" title="Permalink to this definition"></a></dt>
<dd></dd></dl>
<dl class="data">
<dt id="hashlib.blake2s.SALT_SIZE">
<code class="descclassname">blake2s.</code><code class="descname">SALT_SIZE</code><a class="headerlink" href="#hashlib.blake2s.SALT_SIZE" title="Permalink to this definition"></a></dt>
<dd></dd></dl>
<p>Salt length (maximum length accepted by constructors).</p>
<dl class="data">
<dt id="hashlib.blake2b.PERSON_SIZE">
<code class="descclassname">blake2b.</code><code class="descname">PERSON_SIZE</code><a class="headerlink" href="#hashlib.blake2b.PERSON_SIZE" title="Permalink to this definition"></a></dt>
<dd></dd></dl>
<dl class="data">
<dt id="hashlib.blake2s.PERSON_SIZE">
<code class="descclassname">blake2s.</code><code class="descname">PERSON_SIZE</code><a class="headerlink" href="#hashlib.blake2s.PERSON_SIZE" title="Permalink to this definition"></a></dt>
<dd></dd></dl>
<p>Personalization string length (maximum length accepted by constructors).</p>
<dl class="data">
<dt id="hashlib.blake2b.MAX_KEY_SIZE">
<code class="descclassname">blake2b.</code><code class="descname">MAX_KEY_SIZE</code><a class="headerlink" href="#hashlib.blake2b.MAX_KEY_SIZE" title="Permalink to this definition"></a></dt>
<dd></dd></dl>
<dl class="data">
<dt id="hashlib.blake2s.MAX_KEY_SIZE">
<code class="descclassname">blake2s.</code><code class="descname">MAX_KEY_SIZE</code><a class="headerlink" href="#hashlib.blake2s.MAX_KEY_SIZE" title="Permalink to this definition"></a></dt>
<dd></dd></dl>
<p>Maximum key size.</p>
<dl class="data">
<dt id="hashlib.blake2b.MAX_DIGEST_SIZE">
<code class="descclassname">blake2b.</code><code class="descname">MAX_DIGEST_SIZE</code><a class="headerlink" href="#hashlib.blake2b.MAX_DIGEST_SIZE" title="Permalink to this definition"></a></dt>
<dd></dd></dl>
<dl class="data">
<dt id="hashlib.blake2s.MAX_DIGEST_SIZE">
<code class="descclassname">blake2s.</code><code class="descname">MAX_DIGEST_SIZE</code><a class="headerlink" href="#hashlib.blake2s.MAX_DIGEST_SIZE" title="Permalink to this definition"></a></dt>
<dd></dd></dl>
<p>Maximum digest size that the hash function can output.</p>
</div>
<div class="section" id="examples">
<h3>Examples<a class="headerlink" href="#examples" title="Permalink to this headline"></a></h3>
<div class="section" id="simple-hashing">
<h4>Simple hashing<a class="headerlink" href="#simple-hashing" title="Permalink to this headline"></a></h4>
<p>To calculate hash of some data, you should first construct a hash object by
calling the appropriate constructor function (<a class="reference internal" href="#hashlib.blake2b" title="hashlib.blake2b"><code class="xref py py-func docutils literal notranslate"><span class="pre">blake2b()</span></code></a> or
<a class="reference internal" href="#hashlib.blake2s" title="hashlib.blake2s"><code class="xref py py-func docutils literal notranslate"><span class="pre">blake2s()</span></code></a>), then update it with the data by calling <code class="xref py py-meth docutils literal notranslate"><span class="pre">update()</span></code> on the
object, and, finally, get the digest out of the object by calling
<code class="xref py py-meth docutils literal notranslate"><span class="pre">digest()</span></code> (or <code class="xref py py-meth docutils literal notranslate"><span class="pre">hexdigest()</span></code> for hex-encoded string).</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="kn">from</span> <span class="nn">hashlib</span> <span class="k">import</span> <span class="n">blake2b</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">h</span> <span class="o">=</span> <span class="n">blake2b</span><span class="p">()</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">h</span><span class="o">.</span><span class="n">update</span><span class="p">(</span><span class="sa">b</span><span class="s1">&#39;Hello world&#39;</span><span class="p">)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">h</span><span class="o">.</span><span class="n">hexdigest</span><span class="p">()</span>
<span class="go">&#39;6ff843ba685842aa82031d3f53c48b66326df7639a63d128974c5c14f31a0f33343a8c65551134ed1ae0f2b0dd2bb495dc81039e3eeb0aa1bb0388bbeac29183&#39;</span>
</pre></div>
</div>
<p>As a shortcut, you can pass the first chunk of data to update directly to the
constructor as the positional argument:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="kn">from</span> <span class="nn">hashlib</span> <span class="k">import</span> <span class="n">blake2b</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">blake2b</span><span class="p">(</span><span class="sa">b</span><span class="s1">&#39;Hello world&#39;</span><span class="p">)</span><span class="o">.</span><span class="n">hexdigest</span><span class="p">()</span>
<span class="go">&#39;6ff843ba685842aa82031d3f53c48b66326df7639a63d128974c5c14f31a0f33343a8c65551134ed1ae0f2b0dd2bb495dc81039e3eeb0aa1bb0388bbeac29183&#39;</span>
</pre></div>
</div>
<p>You can call <a class="reference internal" href="#hashlib.hash.update" title="hashlib.hash.update"><code class="xref py py-meth docutils literal notranslate"><span class="pre">hash.update()</span></code></a> as many times as you need to iteratively
update the hash:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="kn">from</span> <span class="nn">hashlib</span> <span class="k">import</span> <span class="n">blake2b</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">items</span> <span class="o">=</span> <span class="p">[</span><span class="sa">b</span><span class="s1">&#39;Hello&#39;</span><span class="p">,</span> <span class="sa">b</span><span class="s1">&#39; &#39;</span><span class="p">,</span> <span class="sa">b</span><span class="s1">&#39;world&#39;</span><span class="p">]</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">h</span> <span class="o">=</span> <span class="n">blake2b</span><span class="p">()</span>
<span class="gp">&gt;&gt;&gt; </span><span class="k">for</span> <span class="n">item</span> <span class="ow">in</span> <span class="n">items</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="n">item</span><span class="p">)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">h</span><span class="o">.</span><span class="n">hexdigest</span><span class="p">()</span>
<span class="go">&#39;6ff843ba685842aa82031d3f53c48b66326df7639a63d128974c5c14f31a0f33343a8c65551134ed1ae0f2b0dd2bb495dc81039e3eeb0aa1bb0388bbeac29183&#39;</span>
</pre></div>
</div>
</div>
<div class="section" id="using-different-digest-sizes">
<h4>Using different digest sizes<a class="headerlink" href="#using-different-digest-sizes" title="Permalink to this headline"></a></h4>
<p>BLAKE2 has configurable size of digests up to 64 bytes for BLAKE2b and up to 32
bytes for BLAKE2s. For example, to replace SHA-1 with BLAKE2b without changing
the size of output, we can tell BLAKE2b to produce 20-byte digests:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="kn">from</span> <span class="nn">hashlib</span> <span class="k">import</span> <span class="n">blake2b</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">h</span> <span class="o">=</span> <span class="n">blake2b</span><span class="p">(</span><span class="n">digest_size</span><span class="o">=</span><span class="mi">20</span><span class="p">)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">h</span><span class="o">.</span><span class="n">update</span><span class="p">(</span><span class="sa">b</span><span class="s1">&#39;Replacing SHA1 with the more secure function&#39;</span><span class="p">)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">h</span><span class="o">.</span><span class="n">hexdigest</span><span class="p">()</span>
<span class="go">&#39;d24f26cf8de66472d58d4e1b1774b4c9158b1f4c&#39;</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">h</span><span class="o">.</span><span class="n">digest_size</span>
<span class="go">20</span>
<span class="gp">&gt;&gt;&gt; </span><span class="nb">len</span><span class="p">(</span><span class="n">h</span><span class="o">.</span><span class="n">digest</span><span class="p">())</span>
<span class="go">20</span>
</pre></div>
</div>
<p>Hash objects with different digest sizes have completely different outputs
(shorter hashes are <em>not</em> prefixes of longer hashes); BLAKE2b and BLAKE2s
produce different outputs even if the output length is the same:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="kn">from</span> <span class="nn">hashlib</span> <span class="k">import</span> <span class="n">blake2b</span><span class="p">,</span> <span class="n">blake2s</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">blake2b</span><span class="p">(</span><span class="n">digest_size</span><span class="o">=</span><span class="mi">10</span><span class="p">)</span><span class="o">.</span><span class="n">hexdigest</span><span class="p">()</span>
<span class="go">&#39;6fa1d8fcfd719046d762&#39;</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">blake2b</span><span class="p">(</span><span class="n">digest_size</span><span class="o">=</span><span class="mi">11</span><span class="p">)</span><span class="o">.</span><span class="n">hexdigest</span><span class="p">()</span>
<span class="go">&#39;eb6ec15daf9546254f0809&#39;</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">blake2s</span><span class="p">(</span><span class="n">digest_size</span><span class="o">=</span><span class="mi">10</span><span class="p">)</span><span class="o">.</span><span class="n">hexdigest</span><span class="p">()</span>
<span class="go">&#39;1bf21a98c78a1c376ae9&#39;</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">blake2s</span><span class="p">(</span><span class="n">digest_size</span><span class="o">=</span><span class="mi">11</span><span class="p">)</span><span class="o">.</span><span class="n">hexdigest</span><span class="p">()</span>
<span class="go">&#39;567004bf96e4a25773ebf4&#39;</span>
</pre></div>
</div>
</div>
<div class="section" id="keyed-hashing">
<h4>Keyed hashing<a class="headerlink" href="#keyed-hashing" title="Permalink to this headline"></a></h4>
<p>Keyed hashing can be used for authentication as a faster and simpler
replacement for <a class="reference external" href="https://en.wikipedia.org/wiki/Hash-based_message_authentication_code">Hash-based message authentication code</a> (HMAC).
BLAKE2 can be securely used in prefix-MAC mode thanks to the
indifferentiability property inherited from BLAKE.</p>
<p>This example shows how to get a (hex-encoded) 128-bit authentication code for
message <code class="docutils literal notranslate"><span class="pre">b'message</span> <span class="pre">data'</span></code> with key <code class="docutils literal notranslate"><span class="pre">b'pseudorandom</span> <span class="pre">key'</span></code>:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="kn">from</span> <span class="nn">hashlib</span> <span class="k">import</span> <span class="n">blake2b</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">h</span> <span class="o">=</span> <span class="n">blake2b</span><span class="p">(</span><span class="n">key</span><span class="o">=</span><span class="sa">b</span><span class="s1">&#39;pseudorandom key&#39;</span><span class="p">,</span> <span class="n">digest_size</span><span class="o">=</span><span class="mi">16</span><span class="p">)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">h</span><span class="o">.</span><span class="n">update</span><span class="p">(</span><span class="sa">b</span><span class="s1">&#39;message data&#39;</span><span class="p">)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">h</span><span class="o">.</span><span class="n">hexdigest</span><span class="p">()</span>
<span class="go">&#39;3d363ff7401e02026f4a4687d4863ced&#39;</span>
</pre></div>
</div>
<p>As a practical example, a web application can symmetrically sign cookies sent
to users and later verify them to make sure they weren’t tampered with:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="kn">from</span> <span class="nn">hashlib</span> <span class="k">import</span> <span class="n">blake2b</span>
<span class="gp">&gt;&gt;&gt; </span><span class="kn">from</span> <span class="nn">hmac</span> <span class="k">import</span> <span class="n">compare_digest</span>
<span class="go">&gt;&gt;&gt;</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">SECRET_KEY</span> <span class="o">=</span> <span class="sa">b</span><span class="s1">&#39;pseudorandomly generated server secret key&#39;</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">AUTH_SIZE</span> <span class="o">=</span> <span class="mi">16</span>
<span class="go">&gt;&gt;&gt;</span>
<span class="gp">&gt;&gt;&gt; </span><span class="k">def</span> <span class="nf">sign</span><span class="p">(</span><span class="n">cookie</span><span class="p">):</span>
<span class="gp">... </span> <span class="n">h</span> <span class="o">=</span> <span class="n">blake2b</span><span class="p">(</span><span class="n">digest_size</span><span class="o">=</span><span class="n">AUTH_SIZE</span><span class="p">,</span> <span class="n">key</span><span class="o">=</span><span class="n">SECRET_KEY</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="n">cookie</span><span class="p">)</span>
<span class="gp">... </span> <span class="k">return</span> <span class="n">h</span><span class="o">.</span><span class="n">hexdigest</span><span class="p">()</span><span class="o">.</span><span class="n">encode</span><span class="p">(</span><span class="s1">&#39;utf-8&#39;</span><span class="p">)</span>
<span class="go">&gt;&gt;&gt;</span>
<span class="gp">&gt;&gt;&gt; </span><span class="k">def</span> <span class="nf">verify</span><span class="p">(</span><span class="n">cookie</span><span class="p">,</span> <span class="n">sig</span><span class="p">):</span>
<span class="gp">... </span> <span class="n">good_sig</span> <span class="o">=</span> <span class="n">sign</span><span class="p">(</span><span class="n">cookie</span><span class="p">)</span>
<span class="gp">... </span> <span class="k">return</span> <span class="n">compare_digest</span><span class="p">(</span><span class="n">good_sig</span><span class="p">,</span> <span class="n">sig</span><span class="p">)</span>
<span class="go">&gt;&gt;&gt;</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">cookie</span> <span class="o">=</span> <span class="sa">b</span><span class="s1">&#39;user-alice&#39;</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">sig</span> <span class="o">=</span> <span class="n">sign</span><span class="p">(</span><span class="n">cookie</span><span class="p">)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="nb">print</span><span class="p">(</span><span class="s2">&quot;</span><span class="si">{0}</span><span class="s2">,</span><span class="si">{1}</span><span class="s2">&quot;</span><span class="o">.</span><span class="n">format</span><span class="p">(</span><span class="n">cookie</span><span class="o">.</span><span class="n">decode</span><span class="p">(</span><span class="s1">&#39;utf-8&#39;</span><span class="p">),</span> <span class="n">sig</span><span class="p">))</span>
<span class="go">user-alice,b&#39;43b3c982cf697e0c5ab22172d1ca7421&#39;</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">verify</span><span class="p">(</span><span class="n">cookie</span><span class="p">,</span> <span class="n">sig</span><span class="p">)</span>
<span class="go">True</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">verify</span><span class="p">(</span><span class="sa">b</span><span class="s1">&#39;user-bob&#39;</span><span class="p">,</span> <span class="n">sig</span><span class="p">)</span>
<span class="go">False</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">verify</span><span class="p">(</span><span class="n">cookie</span><span class="p">,</span> <span class="sa">b</span><span class="s1">&#39;0102030405060708090a0b0c0d0e0f00&#39;</span><span class="p">)</span>
<span class="go">False</span>
</pre></div>
</div>
<p>Even though there’s a native keyed hashing mode, BLAKE2 can, of course, be used
in HMAC construction with <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 notranslate"><span class="pre">hmac</span></code></a> module:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="kn">import</span> <span class="nn">hmac</span><span class="o">,</span> <span class="nn">hashlib</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">m</span> <span class="o">=</span> <span class="n">hmac</span><span class="o">.</span><span class="n">new</span><span class="p">(</span><span class="sa">b</span><span class="s1">&#39;secret key&#39;</span><span class="p">,</span> <span class="n">digestmod</span><span class="o">=</span><span class="n">hashlib</span><span class="o">.</span><span class="n">blake2s</span><span class="p">)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">m</span><span class="o">.</span><span class="n">update</span><span class="p">(</span><span class="sa">b</span><span class="s1">&#39;message&#39;</span><span class="p">)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">m</span><span class="o">.</span><span class="n">hexdigest</span><span class="p">()</span>
<span class="go">&#39;e3c8102868d28b5ff85fc35dda07329970d1a01e273c37481326fe0c861c8142&#39;</span>
</pre></div>
</div>
</div>
<div class="section" id="randomized-hashing">
<h4>Randomized hashing<a class="headerlink" href="#randomized-hashing" title="Permalink to this headline"></a></h4>
<p>By setting <em>salt</em> parameter users can introduce randomization to the hash
function. Randomized hashing is useful for protecting against collision attacks
on the hash function used in digital signatures.</p>
<blockquote>
<div><p>Randomized hashing is designed for situations where one party, the message
preparer, generates all or part of a message to be signed by a second
party, the message signer. If the message preparer is able to find
cryptographic hash function collisions (i.e., two messages producing the
same hash value), then they might prepare meaningful versions of the message
that would produce the same hash value and digital signature, but with
different results (e.g., transferring $1,000,000 to an account, rather than
$10). Cryptographic hash functions have been designed with collision
resistance as a major goal, but the current concentration on attacking
cryptographic hash functions may result in a given cryptographic hash
function providing less collision resistance than expected. Randomized
hashing offers the signer additional protection by reducing the likelihood
that a preparer can generate two or more messages that ultimately yield the
same hash value during the digital signature generation process — even if
it is practical to find collisions for the hash function. However, the use
of randomized hashing may reduce the amount of security provided by a
digital signature when all portions of the message are prepared
by the signer.</p>
<p>(<a class="reference external" href="https://csrc.nist.gov/publications/detail/sp/800-106/final">NIST SP-800-106 “Randomized Hashing for Digital Signatures”</a>)</p>
</div></blockquote>
<p>In BLAKE2 the salt is processed as a one-time input to the hash function during
initialization, rather than as an input to each compression function.</p>
<div class="admonition warning">
<p class="admonition-title">Warning</p>
<p><em>Salted hashing</em> (or just hashing) with BLAKE2 or any other general-purpose
cryptographic hash function, such as SHA-256, is not suitable for hashing
passwords. See <a class="reference external" href="https://blake2.net/#qa">BLAKE2 FAQ</a> for more
information.</p>
</div>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="kn">import</span> <span class="nn">os</span>
<span class="gp">&gt;&gt;&gt; </span><span class="kn">from</span> <span class="nn">hashlib</span> <span class="k">import</span> <span class="n">blake2b</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">msg</span> <span class="o">=</span> <span class="sa">b</span><span class="s1">&#39;some message&#39;</span>
<span class="gp">&gt;&gt;&gt; </span><span class="c1"># Calculate the first hash with a random salt.</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">salt1</span> <span class="o">=</span> <span class="n">os</span><span class="o">.</span><span class="n">urandom</span><span class="p">(</span><span class="n">blake2b</span><span class="o">.</span><span class="n">SALT_SIZE</span><span class="p">)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">h1</span> <span class="o">=</span> <span class="n">blake2b</span><span class="p">(</span><span class="n">salt</span><span class="o">=</span><span class="n">salt1</span><span class="p">)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">h1</span><span class="o">.</span><span class="n">update</span><span class="p">(</span><span class="n">msg</span><span class="p">)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="c1"># Calculate the second hash with a different random salt.</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">salt2</span> <span class="o">=</span> <span class="n">os</span><span class="o">.</span><span class="n">urandom</span><span class="p">(</span><span class="n">blake2b</span><span class="o">.</span><span class="n">SALT_SIZE</span><span class="p">)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">h2</span> <span class="o">=</span> <span class="n">blake2b</span><span class="p">(</span><span class="n">salt</span><span class="o">=</span><span class="n">salt2</span><span class="p">)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">h2</span><span class="o">.</span><span class="n">update</span><span class="p">(</span><span class="n">msg</span><span class="p">)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="c1"># The digests are different.</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">h1</span><span class="o">.</span><span class="n">digest</span><span class="p">()</span> <span class="o">!=</span> <span class="n">h2</span><span class="o">.</span><span class="n">digest</span><span class="p">()</span>
<span class="go">True</span>
</pre></div>
</div>
</div>
<div class="section" id="personalization">
<h4>Personalization<a class="headerlink" href="#personalization" title="Permalink to this headline"></a></h4>
<p>Sometimes it is useful to force hash function to produce different digests for
the same input for different purposes. Quoting the authors of the Skein hash
function:</p>
<blockquote>
<div><p>We recommend that all application designers seriously consider doing this;
we have seen many protocols where a hash that is computed in one part of
the protocol can be used in an entirely different part because two hash
computations were done on similar or related data, and the attacker can
force the application to make the hash inputs the same. Personalizing each
hash function used in the protocol summarily stops this type of attack.</p>
<p>(<a class="reference external" href="http://www.skein-hash.info/sites/default/files/skein1.3.pdf">The Skein Hash Function Family</a>,
p. 21)</p>
</div></blockquote>
<p>BLAKE2 can be personalized by passing bytes to the <em>person</em> argument:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="kn">from</span> <span class="nn">hashlib</span> <span class="k">import</span> <span class="n">blake2b</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">FILES_HASH_PERSON</span> <span class="o">=</span> <span class="sa">b</span><span class="s1">&#39;MyApp Files Hash&#39;</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">BLOCK_HASH_PERSON</span> <span class="o">=</span> <span class="sa">b</span><span class="s1">&#39;MyApp Block Hash&#39;</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">h</span> <span class="o">=</span> <span class="n">blake2b</span><span class="p">(</span><span class="n">digest_size</span><span class="o">=</span><span class="mi">32</span><span class="p">,</span> <span class="n">person</span><span class="o">=</span><span class="n">FILES_HASH_PERSON</span><span class="p">)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">h</span><span class="o">.</span><span class="n">update</span><span class="p">(</span><span class="sa">b</span><span class="s1">&#39;the same content&#39;</span><span class="p">)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">h</span><span class="o">.</span><span class="n">hexdigest</span><span class="p">()</span>
<span class="go">&#39;20d9cd024d4fb086aae819a1432dd2466de12947831b75c5a30cf2676095d3b4&#39;</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">h</span> <span class="o">=</span> <span class="n">blake2b</span><span class="p">(</span><span class="n">digest_size</span><span class="o">=</span><span class="mi">32</span><span class="p">,</span> <span class="n">person</span><span class="o">=</span><span class="n">BLOCK_HASH_PERSON</span><span class="p">)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">h</span><span class="o">.</span><span class="n">update</span><span class="p">(</span><span class="sa">b</span><span class="s1">&#39;the same content&#39;</span><span class="p">)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">h</span><span class="o">.</span><span class="n">hexdigest</span><span class="p">()</span>
<span class="go">&#39;cf68fb5761b9c44e7878bfb2c4c9aea52264a80b75005e65619778de59f383a3&#39;</span>
</pre></div>
</div>
<p>Personalization together with the keyed mode can also be used to derive different
keys from a single one.</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="kn">from</span> <span class="nn">hashlib</span> <span class="k">import</span> <span class="n">blake2s</span>
<span class="gp">&gt;&gt;&gt; </span><span class="kn">from</span> <span class="nn">base64</span> <span class="k">import</span> <span class="n">b64decode</span><span class="p">,</span> <span class="n">b64encode</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">orig_key</span> <span class="o">=</span> <span class="n">b64decode</span><span class="p">(</span><span class="sa">b</span><span class="s1">&#39;Rm5EPJai72qcK3RGBpW3vPNfZy5OZothY+kHY6h21KM=&#39;</span><span class="p">)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">enc_key</span> <span class="o">=</span> <span class="n">blake2s</span><span class="p">(</span><span class="n">key</span><span class="o">=</span><span class="n">orig_key</span><span class="p">,</span> <span class="n">person</span><span class="o">=</span><span class="sa">b</span><span class="s1">&#39;kEncrypt&#39;</span><span class="p">)</span><span class="o">.</span><span class="n">digest</span><span class="p">()</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mac_key</span> <span class="o">=</span> <span class="n">blake2s</span><span class="p">(</span><span class="n">key</span><span class="o">=</span><span class="n">orig_key</span><span class="p">,</span> <span class="n">person</span><span class="o">=</span><span class="sa">b</span><span class="s1">&#39;kMAC&#39;</span><span class="p">)</span><span class="o">.</span><span class="n">digest</span><span class="p">()</span>
<span class="gp">&gt;&gt;&gt; </span><span class="nb">print</span><span class="p">(</span><span class="n">b64encode</span><span class="p">(</span><span class="n">enc_key</span><span class="p">)</span><span class="o">.</span><span class="n">decode</span><span class="p">(</span><span class="s1">&#39;utf-8&#39;</span><span class="p">))</span>
<span class="go">rbPb15S/Z9t+agffno5wuhB77VbRi6F9Iv2qIxU7WHw=</span>
<span class="gp">&gt;&gt;&gt; </span><span class="nb">print</span><span class="p">(</span><span class="n">b64encode</span><span class="p">(</span><span class="n">mac_key</span><span class="p">)</span><span class="o">.</span><span class="n">decode</span><span class="p">(</span><span class="s1">&#39;utf-8&#39;</span><span class="p">))</span>
<span class="go">G9GtHFE1YluXY1zWPlYk1e/nWfu0WSEb0KRcjhDeP/o=</span>
</pre></div>
</div>
</div>
<div class="section" id="tree-mode">
<h4>Tree mode<a class="headerlink" href="#tree-mode" title="Permalink to this headline"></a></h4>
<p>Here’s an example of hashing a minimal tree with two leaf nodes:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span> <span class="mi">10</span>
<span class="o">/</span> \
<span class="mi">00</span> <span class="mi">01</span>
</pre></div>
</div>
<p>This example uses 64-byte internal digests, and returns the 32-byte final
digest:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="kn">from</span> <span class="nn">hashlib</span> <span class="k">import</span> <span class="n">blake2b</span>
<span class="go">&gt;&gt;&gt;</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">FANOUT</span> <span class="o">=</span> <span class="mi">2</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">DEPTH</span> <span class="o">=</span> <span class="mi">2</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">LEAF_SIZE</span> <span class="o">=</span> <span class="mi">4096</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">INNER_SIZE</span> <span class="o">=</span> <span class="mi">64</span>
<span class="go">&gt;&gt;&gt;</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">buf</span> <span class="o">=</span> <span class="nb">bytearray</span><span class="p">(</span><span class="mi">6000</span><span class="p">)</span>
<span class="go">&gt;&gt;&gt;</span>
<span class="gp">&gt;&gt;&gt; </span><span class="c1"># Left leaf</span>
<span class="gp">... </span><span class="n">h00</span> <span class="o">=</span> <span class="n">blake2b</span><span class="p">(</span><span class="n">buf</span><span class="p">[</span><span class="mi">0</span><span class="p">:</span><span class="n">LEAF_SIZE</span><span class="p">],</span> <span class="n">fanout</span><span class="o">=</span><span class="n">FANOUT</span><span class="p">,</span> <span class="n">depth</span><span class="o">=</span><span class="n">DEPTH</span><span class="p">,</span>
<span class="gp">... </span> <span class="n">leaf_size</span><span class="o">=</span><span class="n">LEAF_SIZE</span><span class="p">,</span> <span class="n">inner_size</span><span class="o">=</span><span class="n">INNER_SIZE</span><span class="p">,</span>
<span class="gp">... </span> <span class="n">node_offset</span><span class="o">=</span><span class="mi">0</span><span class="p">,</span> <span class="n">node_depth</span><span class="o">=</span><span class="mi">0</span><span class="p">,</span> <span class="n">last_node</span><span class="o">=</span><span class="kc">False</span><span class="p">)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="c1"># Right leaf</span>
<span class="gp">... </span><span class="n">h01</span> <span class="o">=</span> <span class="n">blake2b</span><span class="p">(</span><span class="n">buf</span><span class="p">[</span><span class="n">LEAF_SIZE</span><span class="p">:],</span> <span class="n">fanout</span><span class="o">=</span><span class="n">FANOUT</span><span class="p">,</span> <span class="n">depth</span><span class="o">=</span><span class="n">DEPTH</span><span class="p">,</span>
<span class="gp">... </span> <span class="n">leaf_size</span><span class="o">=</span><span class="n">LEAF_SIZE</span><span class="p">,</span> <span class="n">inner_size</span><span class="o">=</span><span class="n">INNER_SIZE</span><span class="p">,</span>
<span class="gp">... </span> <span class="n">node_offset</span><span class="o">=</span><span class="mi">1</span><span class="p">,</span> <span class="n">node_depth</span><span class="o">=</span><span class="mi">0</span><span class="p">,</span> <span class="n">last_node</span><span class="o">=</span><span class="kc">True</span><span class="p">)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="c1"># Root node</span>
<span class="gp">... </span><span class="n">h10</span> <span class="o">=</span> <span class="n">blake2b</span><span class="p">(</span><span class="n">digest_size</span><span class="o">=</span><span class="mi">32</span><span class="p">,</span> <span class="n">fanout</span><span class="o">=</span><span class="n">FANOUT</span><span class="p">,</span> <span class="n">depth</span><span class="o">=</span><span class="n">DEPTH</span><span class="p">,</span>
<span class="gp">... </span> <span class="n">leaf_size</span><span class="o">=</span><span class="n">LEAF_SIZE</span><span class="p">,</span> <span class="n">inner_size</span><span class="o">=</span><span class="n">INNER_SIZE</span><span class="p">,</span>
<span class="gp">... </span> <span class="n">node_offset</span><span class="o">=</span><span class="mi">0</span><span class="p">,</span> <span class="n">node_depth</span><span class="o">=</span><span class="mi">1</span><span class="p">,</span> <span class="n">last_node</span><span class="o">=</span><span class="kc">True</span><span class="p">)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">h10</span><span class="o">.</span><span class="n">update</span><span class="p">(</span><span class="n">h00</span><span class="o">.</span><span class="n">digest</span><span class="p">())</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">h10</span><span class="o">.</span><span class="n">update</span><span class="p">(</span><span class="n">h01</span><span class="o">.</span><span class="n">digest</span><span class="p">())</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">h10</span><span class="o">.</span><span class="n">hexdigest</span><span class="p">()</span>
<span class="go">&#39;3ad2a9b37c6070e374c7a8c508fe20ca86b6ed54e286e93a0318e95e881db5aa&#39;</span>
</pre></div>
</div>
</div>
</div>
<div class="section" id="credits">
<h3>Credits<a class="headerlink" href="#credits" title="Permalink to this headline"></a></h3>
<p><a class="reference external" href="https://blake2.net">BLAKE2</a> was designed by <em>Jean-Philippe Aumasson</em>, <em>Samuel Neves</em>, <em>Zooko
Wilcox-O’Hearn</em>, and <em>Christian Winnerlein</em> based on <a class="reference external" href="https://en.wikipedia.org/wiki/NIST_hash_function_competition">SHA-3</a> finalist <a class="reference external" href="https://131002.net/blake/">BLAKE</a>
created by <em>Jean-Philippe Aumasson</em>, <em>Luca Henzen</em>, <em>Willi Meier</em>, and
<em>Raphael C.-W. Phan</em>.</p>
<p>It uses core algorithm from <a class="reference external" href="https://cr.yp.to/chacha.html">ChaCha</a> cipher designed by <em>Daniel J. Bernstein</em>.</p>
<p>The stdlib implementation is based on <a class="reference external" href="https://pythonhosted.org/pyblake2/">pyblake2</a> module. It was written by
<em>Dmitry Chestnykh</em> based on C implementation written by <em>Samuel Neves</em>. The
documentation was copied from <a class="reference external" href="https://pythonhosted.org/pyblake2/">pyblake2</a> and written by <em>Dmitry Chestnykh</em>.</p>
<p>The C code was partly rewritten for Python by <em>Christian Heimes</em>.</p>
<p>The following public domain dedication applies for both C hash function
implementation, extension code, and this documentation:</p>
<blockquote>
<div><p>To the extent possible under law, the author(s) have dedicated all copyright
and related and neighboring rights to this software to the public domain
worldwide. This software is distributed without any warranty.</p>
<p>You should have received a copy of the CC0 Public Domain Dedication along
with this software. If not, see
<a class="reference external" href="https://creativecommons.org/publicdomain/zero/1.0/">https://creativecommons.org/publicdomain/zero/1.0/</a>.</p>
</div></blockquote>
<p>The following people have helped with development or contributed their changes
to the project and the public domain according to the Creative Commons Public
Domain Dedication 1.0 Universal:</p>
<ul class="simple">
<li><p><em>Alexandr Sokolovskiy</em></p></li>
</ul>
<div class="admonition seealso">
<p class="admonition-title">See also</p>
<dl class="simple">
<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 notranslate"><span class="pre">hmac</span></code></a></dt><dd><p>A module to generate message authentication codes using hashes.</p>
</dd>
<dt>Module <a class="reference internal" href="base64.html#module-base64" title="base64: RFC 3548: Base16, Base32, Base64 Data Encodings; Base85 and Ascii85"><code class="xref py py-mod docutils literal notranslate"><span class="pre">base64</span></code></a></dt><dd><p>Another way to encode binary hashes for non-binary environments.</p>
</dd>
<dt><a class="reference external" href="https://blake2.net">https://blake2.net</a></dt><dd><p>Official BLAKE2 website.</p>
</dd>
<dt><a class="reference external" href="https://csrc.nist.gov/csrc/media/publications/fips/180/2/archive/2002-08-01/documents/fips180-2.pdf">https://csrc.nist.gov/csrc/media/publications/fips/180/2/archive/2002-08-01/documents/fips180-2.pdf</a></dt><dd><p>The FIPS 180-2 publication on Secure Hash Algorithms.</p>
</dd>
<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><dd><p>Wikipedia article with information on which algorithms have known issues and
what that means regarding their use.</p>
</dd>
<dt><a class="reference external" href="https://www.ietf.org/rfc/rfc2898.txt">https://www.ietf.org/rfc/rfc2898.txt</a></dt><dd><p>PKCS #5: Password-Based Cryptography Specification Version 2.0</p>
</dd>
</dl>
</div>
</div>
</div>
</div>
</div>
</div>
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<h3><a href="../contents.html">Table of Contents</a></h3>
<ul>
<li><a class="reference internal" href="#"><code class="xref py py-mod docutils literal notranslate"><span class="pre">hashlib</span></code> — Secure hashes and message digests</a><ul>
<li><a class="reference internal" href="#hash-algorithms">Hash algorithms</a></li>
<li><a class="reference internal" href="#shake-variable-length-digests">SHAKE variable length digests</a></li>
<li><a class="reference internal" href="#key-derivation">Key derivation</a></li>
<li><a class="reference internal" href="#blake2">BLAKE2</a><ul>
<li><a class="reference internal" href="#creating-hash-objects">Creating hash objects</a></li>
<li><a class="reference internal" href="#constants">Constants</a></li>
<li><a class="reference internal" href="#examples">Examples</a><ul>
<li><a class="reference internal" href="#simple-hashing">Simple hashing</a></li>
<li><a class="reference internal" href="#using-different-digest-sizes">Using different digest sizes</a></li>
<li><a class="reference internal" href="#keyed-hashing">Keyed hashing</a></li>
<li><a class="reference internal" href="#randomized-hashing">Randomized hashing</a></li>
<li><a class="reference internal" href="#personalization">Personalization</a></li>
<li><a class="reference internal" href="#tree-mode">Tree mode</a></li>
</ul>
</li>
<li><a class="reference internal" href="#credits">Credits</a></li>
</ul>
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</ul>
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title="next chapter"><code class="xref py py-mod docutils literal notranslate"><span class="pre">hmac</span></code> — Keyed-Hashing for Message Authentication</a></p>
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