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<refentry xml:id="function.sodium-crypto-box" xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink">
 <refnamediv>
  <refname>sodium_crypto_box</refname>
  <refpurpose>Authenticated public-key encryption</refpurpose>
 </refnamediv>

 <refsect1 role="description">
  &reftitle.description;
  <methodsynopsis>
   <type>string</type><methodname>sodium_crypto_box</methodname>
   <methodparam><type>string</type><parameter>message</parameter></methodparam>
   <methodparam><type>string</type><parameter>nonce</parameter></methodparam>
   <methodparam><type>string</type><parameter>key_pair</parameter></methodparam>
  </methodsynopsis>
  <para>
   Encrypt a message using asymmetric (public key) cryptography.
  </para>
  <para>
   The algorithm used by functions prefixed with <function>sodium_crypto_box</function> are
   Elliptic Curve Diffie-Hellman over the Montgomery curve, Curve25519; usually abbreviated as
   X25519.
  </para>

 </refsect1>

 <refsect1 role="parameters">
  &reftitle.parameters;
  <variablelist>
   <varlistentry>
    <term><parameter>message</parameter></term>
    <listitem>
     <para>
      The message to be encrypted.
     </para>
    </listitem>
   </varlistentry>
   <varlistentry>
    <term><parameter>nonce</parameter></term>
    <listitem>
     <para>
      A number that must be only used once, per message. 24 bytes long.
      This is a large enough bound to generate randomly (i.e. <function>random_bytes</function>).
     </para>
    </listitem>
   </varlistentry>
   <varlistentry>
    <term><parameter>key_pair</parameter></term>
    <listitem>
     <para>
      See <function>sodium_crypto_box_keypair_from_secretkey_and_publickey</function>.
      This should include the sender's X25519 secret key and the recipient's X25519 public key.
     </para>
    </listitem>
   </varlistentry>
  </variablelist>
 </refsect1>

 <refsect1 role="returnvalues">
  &reftitle.returnvalues;
  <para>
   Returns the encrypted message (ciphertext plus authentication tag). The ciphertext will be
   16 bytes longer than the plaintext, and a raw binary string. See <function>sodium_bin2base64</function>
   for safe encoding for storage.
  </para>
 </refsect1>


</refentry>
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