103 lines
5.2 KiB
HTML
103 lines
5.2 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_X25519_DIRTY_FAST(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_X25519_DIRTY_FAST(3monocypher)</td>
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<td class="head-vol">3monocypher</td>
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<td class="head-rtitle">CRYPTO_X25519_DIRTY_FAST(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_x25519_dirty_fast</b>,
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<b class="Nm" title="Nm">crypto_x25519_dirty_small</b> —
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<span class="Nd" title="Nd">generation of Curve25519 points with a low-order
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component</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_x25519_dirty_fast</b>(<var class="Fa" title="Fa">uint8_t
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pk[32]</var>, <var class="Fa" title="Fa">const uint8_t sk[32]</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_x25519_dirty_small</b>(<var class="Fa" title="Fa">uint8_t
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pk[32]</var>, <var class="Fa" title="Fa">const uint8_t sk[32]</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 used in public key generation for
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<a class="Xr" title="Xr" href="crypto_curve_to_hidden.html">crypto_curve_to_hidden(3monocypher)</a>.
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<b class="Sy" title="Sy">This is a highly advanced feature</b>; unless you are
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reading this because you were referred here from
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<a class="Xr" title="Xr" href="crypto_curve_to_hidden.html">crypto_curve_to_hidden(3monocypher)</a>,
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<b class="Sy" title="Sy">you likely have no reason to be using these
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functions</b> and are probably looking for
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<a class="Xr" title="Xr" href="crypto_key_exchange.html">crypto_key_exchange(3monocypher)</a>
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or
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<a class="Xr" title="Xr" href="crypto_x25519.html">crypto_x25519(3monocypher)</a>
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instead. Expect elliptic curve jargon on this page.
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<div class="Pp"></div>
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Both functions generate a Curve25519 public key
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<var class="Fa" title="Fa">pk</var> from the given secret key
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<var class="Fa" title="Fa">sk</var>; the public keys are on the
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<i class="Em" title="Em">whole</i> curve, rather than just the main
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prime-order subgroup. Both do the same with different code size and memory
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characteristics: <b class="Fn" title="Fn">crypto_x25519_dirty_fast</b>() uses
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multiple large temporary variables and uses functions that are normally used
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internally for
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<a class="Xr" title="Xr" href="crypto_sign.html">crypto_sign(3monocypher)</a>;
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accordingly, it uses both more memory (for the temporary variables) and more
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code size (unless the signing code is already compiled in elsewhere).
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<b class="Fn" title="Fn">crypto_x25519_dirty_small</b>() yields the same
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result, but does so using less code and memory at a large performance penalty
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compared to <b class="Fn" title="Fn">crypto_x25519_dirty_fast</b>().
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<div class="Pp"></div>
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The resulting public keys are to be used with
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<a class="Xr" title="Xr" href="crypto_x25519.html">crypto_x25519(3monocypher)</a>
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or
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<a class="Xr" title="Xr" href="crypto_key_exchange.html">crypto_key_exchange(3monocypher)</a>,
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which clear the cofactor.
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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 have no return value. They cannot fail.
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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_curve_to_hidden.html">crypto_curve_to_hidden(3monocypher)</a>,
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<a class="Xr" title="Xr" href="crypto_key_exchange_public_key.html">crypto_key_exchange_public_key(3monocypher)</a>,
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<a class="Xr" title="Xr" href="crypto_x25519_public_key.html">crypto_x25519_public_key(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_x25519_dirty_fast</b>() and
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<b class="Fn" title="Fn">crypto_x25519_dirty_small</b>() functions first
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appeared in Monocypher 3.1.0.
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<h1 class="Sh" title="Sh" id="IMPLEMENTATION_DETAILS"><a class="selflink" href="#IMPLEMENTATION_DETAILS">IMPLEMENTATION
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DETAILS</a></h1>
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The slow variant is approximately an entire two times slower than the fast
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variant. When considering that, on average, two calls to this function will be
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required for obtaining a valid key pair for
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<a class="Xr" title="Xr" href="crypto_curve_to_hidden.html">crypto_curve_to_hidden(3monocypher)</a>,
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this adds up to an <i class="Em" title="Em">average</i> effective slowdown for
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key pair generation of a factor of four.</div>
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<table class="foot">
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<tr>
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<td class="foot-date">March 24, 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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