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+<!DOCTYPE html>
+ <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_SIGN(3MONOCYPHER)</title>
+<table class="head">
+ <tr>
+ <td class="head-ltitle">CRYPTO_SIGN(3MONOCYPHER)</td>
+ <td class="head-vol">3MONOCYPHER</td>
+ <td class="head-rtitle">CRYPTO_SIGN(3MONOCYPHER)</td>
+ </tr>
+<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_sign</b>,
+ <b class="Nm" title="Nm">crypto_check</b>,
+ <b class="Nm" title="Nm">crypto_sign_public_key</b> &#x2014;
+ <span class="Nd" title="Nd">public key signatures</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>
+<b class="Fn" title="Fn">crypto_sign_public_key</b>(<var class="Fa" title="Fa">uint8_t
+ public_key[32]</var>, <var class="Fa" title="Fa">const uint8_t
+ secret_key[32]</var>);
+<div class="Pp"></div>
+<var class="Ft" title="Ft">void</var>
+<b class="Fn" title="Fn">crypto_sign</b>(<var class="Fa" title="Fa">uint8_t
+ signature[64]</var>, <var class="Fa" title="Fa">const uint8_t
+ secret_key[32]</var>, <var class="Fa" title="Fa">const uint8_t
+ public_key[32]</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">int</var>
+<b class="Fn" title="Fn">crypto_check</b>(<var class="Fa" title="Fa">const
+ uint8_t signature[64]</var>, <var class="Fa" title="Fa">const uint8_t
+ public_key[32]</var>, <var class="Fa" title="Fa">const uint8_t *message</var>,
+ <var class="Fa" title="Fa">size_t message_size</var>);
+<h1 class="Sh" title="Sh" id="DESCRIPTION"><a class="selflink" href="#DESCRIPTION">DESCRIPTION</a></h1>
+<b class="Fn" title="Fn">crypto_sign</b>() and
+ <b class="Fn" title="Fn">crypto_check</b>() provide EdDSA public key
+ signatures and verification.
+<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">signature</var></dt>
+ <dd class="It-tag">The signature.</dd>
+ <dt class="It-tag">&#x00A0;</dt>
+ <dd class="It-tag">&#x00A0;</dd>
+ <dt class="It-tag"><var class="Fa" title="Fa">secret_key</var></dt>
+ <dd class="It-tag">A 32-byte random number, known only to you. See
+ <a class="Xr" title="Xr" href="intro.html">intro(3monocypher)</a> about
+ random number generation (use your operating system's random number
+ generator). Do not use the same private key for both signatures and key
+ exchanges. The public keys are different, and revealing both may leak
+ information.</dd>
+ <dt class="It-tag">&#x00A0;</dt>
+ <dd class="It-tag">&#x00A0;</dd>
+ <dt class="It-tag"><var class="Fa" title="Fa">public_key</var></dt>
+ <dd class="It-tag">The public key, generated from
+ <var class="Fa" title="Fa">secret_key</var> with
+ <b class="Fn" title="Fn">crypto_sign_public_key</b>().</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">Message to sign.</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>
+<div class="Pp"></div>
+<var class="Fa" title="Fa">signature</var> and
+ <var class="Fa" title="Fa">message</var> may overlap.
+<div class="Pp"></div>
+<b class="Fn" title="Fn">crypto_sign_public_key</b>() computes the public key of
+ the specified secret key.
+<div class="Pp"></div>
+<b class="Fn" title="Fn">crypto_sign</b>() signs a message with
+ <var class="Fa" title="Fa">secret_key</var>. The public key is optional, and
+ will be recomputed if not provided. This recomputation doubles the execution
+ time.
+<div class="Pp"></div>
+<b class="Fn" title="Fn">crypto_check</b>() checks that a given signature is
+ genuine. Meaning, only someone who had the private key could have signed the
+ message. <b class="Sy" title="Sy">It does not run in constant time</b>. It
+ does not have to in most threat models, because nothing is secret: everyone
+ knows the public key, and the signature and message are rarely secret. If the
+ message needs to be secret, use
+ <a class="Xr" title="Xr" href="crypto_key_exchange.html">crypto_key_exchange(3monocypher)</a>
+ and
+ <a class="Xr" title="Xr" href="crypto_lock_aead.html">crypto_lock_aead(3monocypher)</a>
+ instead.
+<div class="Pp"></div>
+An incremental interface is available; see
+ <a class="Xr" title="Xr" href="crypto_sign_init_first_pass.html">crypto_sign_init_first_pass(3monocypher)</a>.
+<h1 class="Sh" title="Sh" id="RETURN_VALUES"><a class="selflink" href="#RETURN_VALUES">RETURN
+ VALUES</a></h1>
+<b class="Fn" title="Fn">crypto_sign_public_key</b>() and
+ <b class="Fn" title="Fn">crypto_sign</b>() return nothing.
+<div class="Pp"></div>
+<b class="Fn" title="Fn">crypto_check</b>() returns 0 for legitimate messages
+ and -1 for forgeries.
+<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>
+Generate a public key from a random secret key:
+<div class="Pp"></div>
+<div class="Bd" style="margin-left: 5.00ex;">
+<pre class="Li">
+uint8_t sk[32]; /* Random secret key */
+uint8_t pk[32]; /* Matching public key */
+arc4random_buf(sk, 32);
+crypto_sign_public_key(pk, sk);
+/* Wipe the secret key if it is no longer needed */
+crypto_wipe(sk, 32);
+<div class="Pp"></div>
+Sign a message:
+<div class="Pp"></div>
+<div class="Bd" style="margin-left: 5.00ex;">
+<pre class="Li">
+uint8_t sk [32]; /* Secret key from above */
+const uint8_t pk [32]; /* Matching public key */
+const uint8_t message [11] = &quot;Lorem ipsu&quot;; /* Message to sign */
+uint8_t signature[64];
+crypto_sign(signature, sk, pk, message, 10);
+/* Wipe the secret key if it is no longer needed */
+crypto_wipe(sk, 32);
+<div class="Pp"></div>
+Check the above:
+<div class="Pp"></div>
+<div class="Bd" style="margin-left: 5.00ex;">
+<pre class="Li">
+const uint8_t pk [32]; /* Their public key */
+const uint8_t message [11] = &quot;Lorem ipsu&quot;; /* Signed message */
+const uint8_t signature[64]; /* Signature to check */
+if (crypto_check(signature, pk, message, 10)) {
+ /* Message is corrupted, abort processing */
+} else {
+ /* Message is genuine */
+<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_blake2b.html">crypto_blake2b(3monocypher)</a>,
+ <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 PureEdDSA with Curve25519 and Blake2b, as described in
+ RFC 8032. This is the same as Ed25519, with Blake2b instead of SHA-512.
+<h1 class="Sh" title="Sh" id="HISTORY"><a class="selflink" href="#HISTORY">HISTORY</a></h1>
+The <b class="Fn" title="Fn">crypto_sign</b>(),
+ <b class="Fn" title="Fn">crypto_check</b>(), and
+ <b class="Fn" title="Fn">crypto_sign_public_key</b>() functions appeared in
+ Monocypher 0.2.
+<div class="Pp"></div>
+<b class="Sy" title="Sy">A critical security vulnerability</b> that caused
+ all-zero signatures to be accepted was introduced in Monocypher 0.3; it was
+ fixed in Monocypher 1.1.1 and 2.0.4.
+<h1 class="Sh" title="Sh" id="SECURITY_CONSIDERATIONS"><a class="selflink" href="#SECURITY_CONSIDERATIONS">SECURITY
+<h2 class="Ss" title="Ss" id="Signature_malleability"><a class="selflink" href="#Signature_malleability">Signature
+ malleability</a></h2>
+EdDSA signatures are not unique like cryptographic hashes. For any given public
+ key and message, there are many possible valid signatures. Some of them
+ require knowledge of the private key. Others only require knowledge of an
+ existing signature. Observing a valid signature only proves that someone with
+ knowledge of the private key signed the message at some point. Do not rely on
+ any other security property.
+<h2 class="Ss" title="Ss" id="Fault_injection_and_power_analysis"><a class="selflink" href="#Fault_injection_and_power_analysis">Fault
+ injection and power analysis</a></h2>
+Fault injection (also known as glitching) and power analysis may be used to
+ manipulate the resulting signature and recover the secret key in some cases.
+ This requires hardware access. If attackers are expected to have such access
+ and have the relevant equipment, you may try use the incremental interface
+ provided by
+ <a class="Xr" title="Xr" href="crypto_sign_init_first_pass.html">crypto_sign_init_first_pass(3monocypher)</a>
+ to mitigate the side channel attacks. Note that there may still be other
+ power-related side channels (such as if the CPU leaks information when an
+ operation overflows a register) that must be considered.</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>