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