107 lines
5.2 KiB
HTML
107 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_FROM_EDDSA_PRIVATE(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_FROM_EDDSA_PRIVATE(3MONOCYPHER)</td>
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<td class="head-vol">3MONOCYPHER</td>
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<td class="head-rtitle">CRYPTO_FROM_EDDSA_PRIVATE(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_from_eddsa_private</b>,
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<b class="Nm" title="Nm">crypto_from_eddsa_public</b> —
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<span class="Nd" title="Nd">conversion of key pairs for EdDSA with BLAKE2b to
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X25519 key pairs</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_from_eddsa_private</b>(<var class="Fa" title="Fa">uint8_t
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x25519[32]</var>, <var class="Fa" title="Fa">const uint8_t eddsa[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_from_eddsa_public</b>(<var class="Fa" title="Fa">uint8_t
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x25519[32]</var>, <var class="Fa" title="Fa">const uint8_t eddsa[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 convert keys for use with
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<a class="Xr" title="Xr" href="crypto_sign.html">crypto_sign(3monocypher)</a>
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(EdDSA with the BLAKE2b hash function) to keys for use with
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<a class="Xr" title="Xr" href="crypto_key_exchange.html">crypto_key_exchange(3monocypher)</a>
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and
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<a class="Xr" title="Xr" href="crypto_x25519.html">crypto_x25519(3monocypher)</a>.
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This may be useful in some resource-constrained contexts or when no other key
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is available (for example, when retrieving SSH public keys from GitHub and
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reusing the SSH public keys as X25519 public keys).
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<div class="Pp"></div>
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The <b class="Fn" title="Fn">crypto_from_eddsa_private</b>() function converts
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an EdDSA (with BLAKE2b) private key to an X25519 private key. The
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<b class="Fn" title="Fn">crypto_from_eddsa_public</b>() function converts an
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EdDSA public key to an X25519 public key.
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<div class="Pp"></div>
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X25519 key pairs cannot be converted back to EdDSA key pairs. The conversion of
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private keys is specific to EdDSA with BLAKE2b because of the way EdDSA works.
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In particular, this means that the output of
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<b class="Fn" title="Fn">crypto_from_eddsa_private</b>() differs from
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<a class="Xr" title="Xr" href="crypto_from_ed25519_private.html">crypto_from_ed25519_private(3monocypher)</a>
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in the optional code. However, the output of
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<b class="Fn" title="Fn">crypto_from_eddsa_public</b>() is identical to
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<a class="Xr" title="Xr" href="crypto_from_ed25519_public.html">crypto_from_ed25519_public(3monocypher)</a>.
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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">eddsa</var></dt>
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<dd class="It-tag">The signing public key or private key to convert to a
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X25519 public key or private key, respectively.</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">x25519</var></dt>
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<dd class="It-tag">The converted private key or public key.</dd>
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</dl>
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<div class="Pp"></div>
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The arguments may overlap or point at the same buffer.
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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. 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_key_exchange_public_key.html">crypto_key_exchange_public_key(3monocypher)</a>,
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<a class="Xr" title="Xr" href="crypto_sign_public_key.html">crypto_sign_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_from_eddsa_private</b>() and
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<b class="Fn" title="Fn">crypto_from_eddsa_public</b>() functions first
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appeared in Monocypher 3.1.0.
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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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It is generally considered poor form to reuse the same key for different
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purposes. While this conversion is technically safe, avoid these functions
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nonetheless unless you are particularly resource-constrained or have some
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other kind of hard requirement. It is otherwise an unnecessary risk
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factor.</div>
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<table class="foot">
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<tr>
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<td class="foot-date">March 25, 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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