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+<!DOCTYPE html>
+<html>
+<head>
+ <meta charset="utf-8"/>
+ <style>
+ table.head, table.foot { width: 100%; }
+ td.head-rtitle, td.foot-os { text-align: right; }
+ td.head-vol { text-align: center; }
+ div.Pp { margin: 1ex 0ex; }
+ </style>
+ <link rel="stylesheet" href="style.css" type="text/css" media="all"/>
+ <title>CRYPTO_BLAKE2B(3MONOCYPHER)</title>
+</head>
+<body>
+<table class="head">
+ <tr>
+ <td class="head-ltitle">CRYPTO_BLAKE2B(3MONOCYPHER)</td>
+ <td class="head-vol">3MONOCYPHER</td>
+ <td class="head-rtitle">CRYPTO_BLAKE2B(3MONOCYPHER)</td>
+ </tr>
+</table>
+<div class="manual-text">
+<h1 class="Sh" title="Sh" id="NAME"><a class="selflink" href="#NAME">NAME</a></h1>
+<b class="Nm" title="Nm">crypto_blake2b</b>,
+ <b class="Nm" title="Nm">crypto_blake2b_general</b>,
+ <b class="Nm" title="Nm">crypto_blake2b_general_init</b>,
+ <b class="Nm" title="Nm">crypto_blake2b_init</b>,
+ <b class="Nm" title="Nm">crypto_blake2b_update</b>,
+ <b class="Nm" title="Nm">crypto_blake2b_final</b> &#x2014;
+ <span class="Nd" title="Nd">cryptographic hashing</span>
+<h1 class="Sh" title="Sh" id="SYNOPSIS"><a class="selflink" href="#SYNOPSIS">SYNOPSIS</a></h1>
+<b class="In" title="In">#include
+ &lt;<a class="In" title="In">monocypher.h</a>&gt;</b>
+<div class="Pp"></div>
+<var class="Ft" title="Ft">void</var>
+<br/>
+<b class="Fn" title="Fn">crypto_blake2b</b>(<var class="Fa" title="Fa">uint8_t
+ hash[64]</var>, <var class="Fa" title="Fa">const uint8_t *message</var>,
+ <var class="Fa" title="Fa">size_t message_size</var>);
+<div class="Pp"></div>
+<var class="Ft" title="Ft">void</var>
+<br/>
+<b class="Fn" title="Fn">crypto_blake2b_general</b>(<var class="Fa" title="Fa">uint8_t
+ *hash</var>, <var class="Fa" title="Fa">size_t hash_size</var>,
+ <var class="Fa" title="Fa">const uint8_t *key</var>,
+ <var class="Fa" title="Fa">size_t key_size</var>,
+ <var class="Fa" title="Fa">const uint8_t *message</var>,
+ <var class="Fa" title="Fa">size_t message_size</var>);
+<div class="Pp"></div>
+<var class="Ft" title="Ft">void</var>
+<br/>
+<b class="Fn" title="Fn">crypto_blake2b_init</b>(<var class="Fa" title="Fa">crypto_blake2b_ctx
+ *ctx</var>);
+<div class="Pp"></div>
+<var class="Ft" title="Ft">void</var>
+<br/>
+<b class="Fn" title="Fn">crypto_blake2b_general_init</b>(<var class="Fa" title="Fa">crypto_blake2b_ctx
+ *ctx</var>, <var class="Fa" title="Fa">size_t hash_size</var>,
+ <var class="Fa" title="Fa">const uint8_t *key</var>,
+ <var class="Fa" title="Fa">size_t key_size</var>);
+<div class="Pp"></div>
+<var class="Ft" title="Ft">void</var>
+<br/>
+<b class="Fn" title="Fn">crypto_blake2b_update</b>(<var class="Fa" title="Fa">crypto_blake2b_ctx
+ *ctx</var>, <var class="Fa" title="Fa">const uint8_t *message</var>,
+ <var class="Fa" title="Fa">size_t message_size</var>);
+<div class="Pp"></div>
+<var class="Ft" title="Ft">void</var>
+<br/>
+<b class="Fn" title="Fn">crypto_blake2b_final</b>(<var class="Fa" title="Fa">crypto_blake2b_ctx
+ *ctx</var>, <var class="Fa" title="Fa">uint8_t *hash</var>);
+<h1 class="Sh" title="Sh" id="DESCRIPTION"><a class="selflink" href="#DESCRIPTION">DESCRIPTION</a></h1>
+BLAKE2b is a fast cryptographically secure hash, based on the ideas of Chacha20.
+ It is faster than MD5, yet just as secure as SHA-3.
+<div class="Pp"></div>
+Note that BLAKE2b itself is not suitable for hashing passwords and deriving keys
+ from them; use the
+ <a class="Xr" title="Xr" href="crypto_argon2i.html">crypto_argon2i(3monocypher)</a>
+ family of functions for that purpose instead.
+<div class="Pp"></div>
+BLAKE2b is immune to length extension attacks, and as such does not require any
+ specific precautions, such as using the HMAC algorithm.
+<div class="Pp"></div>
+The arguments are:
+<dl class="Bl-tag">
+ <dt class="It-tag">&#x00A0;</dt>
+ <dd class="It-tag">&#x00A0;</dd>
+ <dt class="It-tag"><var class="Fa" title="Fa">hash</var></dt>
+ <dd class="It-tag">The output hash.</dd>
+ <dt class="It-tag">&#x00A0;</dt>
+ <dd class="It-tag">&#x00A0;</dd>
+ <dt class="It-tag"><var class="Fa" title="Fa">hash_size</var></dt>
+ <dd class="It-tag">Length of <var class="Fa" title="Fa">hash</var>, in bytes.
+ Must be between 1 and 64. Anything below 32 is discouraged when using
+ Blake2b as a general-purpose hash function; anything below 16 is
+ discouraged when using Blake2b as a message authentication code.</dd>
+ <dt class="It-tag">&#x00A0;</dt>
+ <dd class="It-tag">&#x00A0;</dd>
+ <dt class="It-tag"><var class="Fa" title="Fa">key</var></dt>
+ <dd class="It-tag">Some secret key. One cannot predict the final hash without
+ it. May be <code class="Dv" title="Dv">NULL</code> if
+ <var class="Fa" title="Fa">key_size</var> is 0, in which case no key is
+ used. Keys can be used to create a message authentication code (MAC). Use
+ <a class="Xr" title="Xr" href="crypto_verify16.html">crypto_verify16(3monocypher)</a>,
+ <a class="Xr" title="Xr" href="crypto_verify32.html">crypto_verify32(3monocypher)</a>,
+ or
+ <a class="Xr" title="Xr" href="crypto_verify64.html">crypto_verify64(3monocypher)</a>
+ to compare MACs created this way. Choose the size of the hash accordingly.
+ Users may want to wipe the key with
+ <a class="Xr" title="Xr" href="crypto_wipe.html">crypto_wipe(3monocypher)</a>
+ once they are done with it.</dd>
+ <dt class="It-tag">&#x00A0;</dt>
+ <dd class="It-tag">&#x00A0;</dd>
+ <dt class="It-tag"><var class="Fa" title="Fa">key_size</var></dt>
+ <dd class="It-tag">Length of <var class="Fa" title="Fa">key</var>, in bytes.
+ Must be between 0 and 64. 32 is a good default.</dd>
+ <dt class="It-tag">&#x00A0;</dt>
+ <dd class="It-tag">&#x00A0;</dd>
+ <dt class="It-tag"><var class="Fa" title="Fa">message</var></dt>
+ <dd class="It-tag">The message to hash. May overlap with
+ <var class="Fa" title="Fa">hash</var>. May be
+ <code class="Dv" title="Dv">NULL</code> if
+ <var class="Fa" title="Fa">message_size</var> is 0.</dd>
+ <dt class="It-tag">&#x00A0;</dt>
+ <dd class="It-tag">&#x00A0;</dd>
+ <dt class="It-tag"><var class="Fa" title="Fa">message_size</var></dt>
+ <dd class="It-tag">Length of <var class="Fa" title="Fa">message</var>, in
+ bytes.</dd>
+</dl>
+<h2 class="Ss" title="Ss" id="Direct_interface"><a class="selflink" href="#Direct_interface">Direct
+ interface</a></h2>
+The direct interface has two functions,
+ <b class="Fn" title="Fn">crypto_blake2b</b>() and
+ <b class="Fn" title="Fn">crypto_blake2b_general</b>().
+ <b class="Fn" title="Fn">crypto_blake2b</b>() is provided for convenience, and
+ is equivalent to calling <b class="Fn" title="Fn">crypto_blake2b_general</b>()
+ with no key and a 64-byte hash.
+<div class="Pp"></div>
+<b class="Fn" title="Fn">crypto_blake2b_general</b>() users can specify the size
+ of the hash, and use a secret key to make the hash unpredictable &#x2013;
+ useful for message authentication codes. Even when using a key, you do not
+ have to wipe the context struct with
+ <a class="Xr" title="Xr" href="crypto_wipe.html">crypto_wipe(3monocypher)</a>.
+<h2 class="Ss" title="Ss" id="Incremental_interface"><a class="selflink" href="#Incremental_interface">Incremental
+ interface</a></h2>
+The incremental interface is useful for handling streams of data or large files
+ without using too much memory. This interface uses three steps:
+<ul class="Bl-bullet">
+ <li class="It-bullet">initialisation with
+ <b class="Fn" title="Fn">crypto_blake2b_general_init</b>() or
+ <b class="Fn" title="Fn">crypto_blake2b_init</b>(), which sets up a
+ context with the hashing parameters;</li>
+ <li class="It-bullet">update with
+ <b class="Fn" title="Fn">crypto_blake2b_update</b>(), which hashes the
+ message chunk by chunk, and keep the intermediary result in the
+ context;</li>
+ <li class="It-bullet">and finalisation with
+ <b class="Fn" title="Fn">crypto_blake2b_final</b>(), which produces the
+ final hash. The <var class="Ft" title="Ft">crypto_blake2b_ctx</var> is
+ automatically wiped upon finalisation.</li>
+</ul>
+<div class="Pp"></div>
+The invariants of the parameters are the same as for
+ <b class="Fn" title="Fn">crypto_blake2b_general</b>().
+ <b class="Fn" title="Fn">crypto_blake2b_init</b>() is a convenience
+ initialisation function that specifies a 64-byte hash and no key. This is
+ considered a good default.
+<h1 class="Sh" title="Sh" id="RETURN_VALUES"><a class="selflink" href="#RETURN_VALUES">RETURN
+ VALUES</a></h1>
+These functions return nothing.
+<h1 class="Sh" title="Sh" id="EXAMPLES"><a class="selflink" href="#EXAMPLES">EXAMPLES</a></h1>
+The following examples assume the existence of
+ <b class="Fn" title="Fn">arc4random_buf</b>(), which fills the given buffer
+ with cryptographically secure random bytes. If
+ <b class="Fn" title="Fn">arc4random_buf</b>() does not exist on your system,
+ see <a class="Xr" title="Xr" href="intro.html">intro(3monocypher)</a> for
+ advice about how to generate cryptographically secure random bytes.
+<div class="Pp"></div>
+Hashing a message all at once:
+<div class="Pp"></div>
+<div class="Bd" style="margin-left: 5.00ex;">
+<pre class="Li">
+uint8_t hash [64]; /* Output hash (64 bytes) */
+uint8_t message[12] = &quot;Lorem ipsum&quot;; /* Message to hash */
+crypto_blake2b(hash, message, 12);
+</pre>
+</div>
+<div class="Pp"></div>
+Computing a message authentication code all at once:
+<div class="Pp"></div>
+<div class="Bd" style="margin-left: 5.00ex;">
+<pre class="Li">
+uint8_t hash [16];
+uint8_t key [32];
+uint8_t message[11] = &quot;Lorem ipsu&quot;; /* Message to authenticate */
+arc4random_buf(key, 32);
+crypto_blake2b_general(hash, 16, key, 32, message, 11);
+/* Wipe secrets if they are no longer needed */
+crypto_wipe(message, 11);
+crypto_wipe(key, 32);
+</pre>
+</div>
+<div class="Pp"></div>
+Hashing a message incrementally (without a key):
+<div class="Pp"></div>
+<div class="Bd" style="margin-left: 5.00ex;">
+<pre class="Li">
+uint8_t hash [ 64]; /* Output hash (64 bytes) */
+uint8_t message[500] = {1}; /* Message to hash */
+crypto_blake2b_ctx ctx;
+crypto_blake2b_init(&amp;ctx);
+for (size_t i = 0; i &lt; 500; i += 100) {
+ crypto_blake2b_update(&amp;ctx, message + i, 100);
+}
+crypto_blake2b_final(&amp;ctx, hash);
+</pre>
+</div>
+<div class="Pp"></div>
+Computing a message authentication code incrementally:
+<div class="Pp"></div>
+<div class="Bd" style="margin-left: 5.00ex;">
+<pre class="Li">
+uint8_t hash [ 16];
+uint8_t key [ 32];
+uint8_t message[500] = {1}; /* Message to authenticate */
+crypto_blake2b_ctx ctx;
+arc4random_buf(key, 32);
+crypto_blake2b_general_init(&amp;ctx, 16, key, 32);
+/* Wipe the key */
+crypto_wipe(key, 32);
+for (size_t i = 0; i &lt; 500; i += 100) {
+ crypto_blake2b_update(&amp;ctx, message + i, 100);
+ /* Wipe secrets if they are no longer needed */
+ crypto_wipe(message + i, 100);
+}
+crypto_blake2b_final(&amp;ctx, hash);
+</pre>
+</div>
+<h1 class="Sh" title="Sh" id="SEE_ALSO"><a class="selflink" href="#SEE_ALSO">SEE
+ ALSO</a></h1>
+<a class="Xr" title="Xr" href="crypto_key_exchange.html">crypto_key_exchange(3monocypher)</a>,
+ <a class="Xr" title="Xr" href="crypto_lock.html">crypto_lock(3monocypher)</a>,
+ <a class="Xr" title="Xr" href="intro.html">intro(3monocypher)</a>
+<h1 class="Sh" title="Sh" id="STANDARDS"><a class="selflink" href="#STANDARDS">STANDARDS</a></h1>
+These functions implement BLAKE2b, described in RFC 7693.
+<h1 class="Sh" title="Sh" id="HISTORY"><a class="selflink" href="#HISTORY">HISTORY</a></h1>
+The <b class="Fn" title="Fn">crypto_blake2b</b>(),
+ <b class="Fn" title="Fn">crypto_blake2b_general</b>(),
+ <b class="Fn" title="Fn">crypto_blake2b_general_init</b>(),
+ <b class="Fn" title="Fn">crypto_blake2b_init</b>(),
+ <b class="Fn" title="Fn">crypto_blake2b_update</b>(), and
+ <b class="Fn" title="Fn">crypto_blake2b_final</b>() functions first appeared
+ in Monocypher 0.1.
+<h1 class="Sh" title="Sh" id="CAVEATS"><a class="selflink" href="#CAVEATS">CAVEATS</a></h1>
+Monocypher does not perform any input validation. Any deviation from the
+ specified input and output length ranges results in
+ <b class="Sy" title="Sy">undefined behaviour</b>. Make sure your inputs are
+ correct.
+<h1 class="Sh" title="Sh" id="SECURITY_CONSIDERATIONS"><a class="selflink" href="#SECURITY_CONSIDERATIONS">SECURITY
+ CONSIDERATIONS</a></h1>
+BLAKE2b is a general-purpose cryptographic hash function; this means that it is
+ not suited for hashing passwords and deriving cryptographic keys from
+ passwords in particular. While cryptographic keys usually have hundreds of
+ bits of entropy, passwords are often much less complex. When storing passwords
+ as hashes or when deriving keys from them, the goal is normally to prevent
+ attackers from quickly iterating all possible passwords. Because passwords
+ tend to be simple, it is important to artificially slow down attackers by
+ using especially computationally difficult hashing algorithms. Monocypher
+ therefore provides
+ <a class="Xr" title="Xr" href="crypto_argon2i.html">crypto_argon2i(3monocypher)</a>
+ for password hashing and deriving keys from passwords.</div>
+<table class="foot">
+ <tr>
+ <td class="foot-date">March 31, 2020</td>
+ <td class="foot-os">Linux 4.15.0-106-generic</td>
+ </tr>
+</table>
+</body>
+</html>