268 lines
12 KiB
HTML
268 lines
12 KiB
HTML
<!DOCTYPE html>
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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_SIGN_INIT_FIRST_PASS_CUSTOM_HASH(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_SIGN_INIT_FIRST_PASS_CUSTOM_HASH(3MONOCYPHER)</td>
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<td class="head-vol">3MONOCYPHER</td>
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<td class="head-rtitle">CRYPTO_SIGN_INIT_FIRST_PASS_CUSTOM_HASH(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_sign_init_first_pass_custom_hash</b>,
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<b class="Nm" title="Nm">crypto_sign_public_key_custom_hash</b>,
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<b class="Nm" title="Nm">crypto_check_init_custom_hash</b> —
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<span class="Nd" title="Nd">public key signatures with custom hash
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functions</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_sign_init_first_pass_custom_hash</b>(<var class="Fa" title="Fa">crypto_sign_ctx_abstract
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*ctx</var>, <var class="Fa" title="Fa">const uint8_t secret_key[32]</var>,
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<var class="Fa" title="Fa">const uint8_t public_key[32]</var>,
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<var class="Fa" title="Fa">const crypto_sign_vtable *hash</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_sign_public_key_custom_hash</b>(<var class="Fa" title="Fa">uint8_t
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public_key[32]</var>, <var class="Fa" title="Fa">const uint8_t
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secret_key[32]</var>, <var class="Fa" title="Fa">const crypto_sign_vtable
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*hash</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_check_init_custom_hash</b>(<var class="Fa" title="Fa">crypto_sign_ctx_abstract
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*ctx</var>, <var class="Fa" title="Fa">const uint8_t signature[64]</var>,
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<var class="Fa" title="Fa">const uint8_t public_key[32]</var>,
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<var class="Fa" title="Fa">const crypto_sign_vtable *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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These functions are variants of the
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<a class="Xr" title="Xr" href="crypto_sign_init_first_pass.html">crypto_sign_init_first_pass(3monocypher)</a>
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family of functions: They provide the ability to replace the EdDSA hash
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function with any user-provided hash function.
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<div class="Pp"></div>
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<b class="Sy" title="Sy">This is a highly advanced feature</b>. Interoperability
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of public key signatures with other cryptographic libraries can normally be
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achieved by using
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<a class="Xr" title="Xr" href="crypto_ed25519_sign.html">crypto_ed25519_sign(3monocypher)</a>
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or
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<a class="Xr" title="Xr" href="crypto_ed25519_sign_init_first_pass.html">crypto_ed25519_sign_init_first_pass(3monocypher)</a>
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already. This interface is exposed only for completeness and to handle special
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situations (e.g. to use the hash function of the future winner of the NIST
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lightweight crypto competition on a device with highly constrained resources
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or taking advantage of hardware support for cryptographic hash functions).
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Whenever possible, these functions should be avoided.
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<div class="Pp"></div>
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To make available a custom hash algorithm for use with these functions, a
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<var class="Vt" title="Vt">crypto_sign_vtable</var> structure must be
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provided. It is defined as:
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<div class="Pp"></div>
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<div class="Bd" style="margin-left: 0.00ex;">
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<pre class="Li">
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typedef struct {
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void (*hash)(uint8_t hash[64], const uint8_t *message,
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size_t message_size);
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void (*init )(void *ctx);
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void (*update)(void *ctx, const uint8_t *message,
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size_t message_size);
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void (*final )(void *ctx, uint8_t hash[64]);
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size_t ctx_size;
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} crypto_sign_vtable;
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</pre>
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</div>
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<div class="Pp"></div>
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The context argument to the functions shall be referred to as “outer
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signing context”. The outer signing context must contain a
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<var class="Vt" title="Vt">crypto_sign_ctx_abstract</var> as
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<i class="Em" title="Em">its first member</i>. Other than that, the outer
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signing context may be defined freely. Logically, it is required to contain
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some kind of hash context as well, else it cannot work as a custom hash
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function.
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<div class="Pp"></div>
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Because the calling code cannot know the real type of the outer signing context,
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it is cast to <var class="Vt" title="Vt">void *</var> when calling the hash
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functions in the vtable, but the <var class="Fa" title="Fa">ctx</var> argument
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to the functions in the vtable is always guaranteed to be the outer signing
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context.
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<div class="Pp"></div>
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The hash functions must not fail. If they somehow can fail, they have no way to
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propagate its error status, and thus the only ways to handle errors are to
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either assume an error never occurs (if reasonable), or to induce a crash in
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the code when an error occurs.
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<div class="Pp"></div>
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The fields of <var class="Vt" title="Vt">crypto_sign_vtable</var> 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">Function that computes a 64-byte hash for a given message
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and writes the computed hash to <var class="Fa" title="Fa">hash</var>. The
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output length <i class="Em" title="Em">must</i> be exactly 64 bytes. This
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will normally be constructed using the functions that provide the
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<var class="Fa" title="Fa">init</var>,
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<var class="Fa" title="Fa">update</var> and
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<var class="Fa" title="Fa">final</var> members.</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">init</var></dt>
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<dd class="It-tag">Function that initialises the hash context of an outer
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signing context.</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">update</var></dt>
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<dd class="It-tag">Function that updates the hash context of an outer signing
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context. It must be able to handle message sizes of at least 32
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bytes.</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">final</var></dt>
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<dd class="It-tag">Function that finalises the hash context of an outer
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signing context and writes the computed hash to
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<var class="Fa" title="Fa">hash</var>. The output length
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<i class="Em" title="Em">must</i> be exactly 64 bytes. This function
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should wipe the hash context with
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<a class="Xr" title="Xr" href="crypto_wipe.html">crypto_wipe(3monocypher)</a>
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if it contains pointers to objects outside the outer signing context.
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Monocypher takes care of wiping the outer signing context.</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">ctx_size</var></dt>
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<dd class="It-tag">The size of the outer signing context as determined by
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<b class="Fn" title="Fn">sizeof</b>().</dd>
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</dl>
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<div class="Pp"></div>
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The functions indicated in the
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<var class="Vt" title="Vt">crypto_sign_vtable</var> must be thread-safe if any
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of Monocypher's signing functions are accessed from multiple threads.
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<div class="Pp"></div>
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After calling
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<b class="Fn" title="Fn">crypto_sign_init_first_pass_custom_hash</b>() or
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<b class="Fn" title="Fn">crypto_check_init_custom_hash</b>(), the
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<a class="Xr" title="Xr" href="crypto_sign_update.html">crypto_sign_update(3monocypher)</a>,
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<a class="Xr" title="Xr" href="crypto_sign_final.html">crypto_sign_final(3monocypher)</a>,
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<a class="Xr" title="Xr" href="crypto_sign_init_second_pass.html">crypto_sign_init_second_pass(3monocypher)</a>,
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<a class="Xr" title="Xr" href="crypto_check_update.html">crypto_check_update(3monocypher)</a>,
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and
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<a class="Xr" title="Xr" href="crypto_check_final.html">crypto_check_final(3monocypher)</a>
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functions can be used as usual. They will call into the hash vtable as
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required. The same security considerations and semantics apply.
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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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Defining and using a custom implementation of SHA-512 and crudely checking its
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results against
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<a class="Xr" title="Xr" href="crypto_ed25519_sign.html">crypto_ed25519_sign(3monocypher)</a>:
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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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struct outer_ctx {
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crypto_sign_ctx_abstract sctx;
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SHA2_CTX hash_ctx;
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};
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static void
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my_hash(uint8_t hash[64], const uint8_t *msg, size_t len)
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{
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SHA2_CTX ctx;
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SHA512Init(&ctx);
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SHA512Update(&ctx, msg, len);
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SHA512Final(hash, &ctx);
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}
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static void
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my_init(void *ctx)
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{
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struct outer_ctx *octx = (struct outer_ctx *)ctx;
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SHA512Init(&octx->hash_ctx);
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}
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static void
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my_update(void *ctx, const uint8_t *msg, size_t len)
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{
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struct outer_ctx *octx = (struct outer_ctx *)ctx;
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SHA512Update(&octx->hash_ctx, msg, len);
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}
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static void
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my_final(void *ctx, uint8_t *hash)
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{
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struct outer_ctx *octx = (struct outer_ctx *)ctx;
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SHA512Final(hash, &octx->hash_ctx);
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}
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static const crypto_sign_vtable my_vtable = {
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my_hash,
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my_init,
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my_update,
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my_final,
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sizeof(struct outer_ctx)
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};
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int
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main(void)
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{
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uint8_t theirs[64], mine[64];
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uint8_t sk[32] = {0x01, 0x02, 0x03, 0x04};
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const uint8_t msg[] = {
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0x00, 0x01, 0x02, 0x04
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};
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crypto_ed25519_sign(theirs, sk, NULL, msg, sizeof(msg));
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struct outer_ctx ctx;
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crypto_sign_ctx_abstract *actx = (crypto_sign_ctx_abstract*)&ctx;
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crypto_sign_init_first_pass_custom_hash(actx,
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sk, NULL, &my_vtable);
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crypto_wipe(sk, sizeof(sk));
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crypto_sign_update( actx, msg, sizeof(msg));
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crypto_sign_init_second_pass(actx);
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crypto_sign_update( actx, msg, sizeof(msg));
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crypto_sign_final( actx, mine);
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if (crypto_verify64(theirs, mine) != 0) {
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fprintf(stderr, "theirs != mine\n");
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return 1;
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}
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puts("ok");
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return 0;
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}
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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_blake2b.html">crypto_blake2b(3monocypher)</a>,
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<a class="Xr" title="Xr" href="crypto_sha512.html">crypto_sha512(3monocypher)</a>,
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<a class="Xr" title="Xr" href="crypto_sign.html">crypto_sign(3monocypher)</a>,
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<a class="Xr" title="Xr" href="crypto_sign_init_first_pass.html">crypto_sign_init_first_pass(3monocypher)</a>,
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<a class="Xr" title="Xr" href="crypto_wipe.html">crypto_wipe(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="HISTORY"><a class="selflink" href="#HISTORY">HISTORY</a></h1>
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The <b class="Fn" title="Fn">crypto_sign_init_first_pass_custom_hash</b>(),
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<b class="Fn" title="Fn">crypto_sign_public_key_custom_hash</b>(),
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<b class="Fn" title="Fn">crypto_check_init_first_pass_custom_hash</b>()
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functions first appeared in Monocypher 3.0.0.</div>
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<table class="foot">
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<tr>
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<td class="foot-date">December 28, 2019</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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