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<?xml version="1.0" encoding="utf-8"?>
<refentry xml:id="function.sodium-crypto-stream-xchacha20-xor-ic" xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink">
<refnamediv>
<refname>sodium_crypto_stream_xchacha20_xor_ic</refname>
<refpurpose>Encrypts a message using a nonce and a secret key (no authentication)</refpurpose>
</refnamediv>
<refsect1 role="description">
&reftitle.description;
<methodsynopsis>
<type>string</type><methodname>sodium_crypto_stream_xchacha20_xor_ic</methodname>
<methodparam><modifier role="attribute">#[\SensitiveParameter]</modifier><type>string</type><parameter>message</parameter></methodparam>
<methodparam><type>string</type><parameter>nonce</parameter></methodparam>
<methodparam><type>int</type><parameter>counter</parameter></methodparam>
<methodparam><modifier role="attribute">#[\SensitiveParameter]</modifier><type>string</type><parameter>key</parameter></methodparam>
</methodsynopsis>
<para>
The function is similar to <function>sodium_crypto_stream_xchacha20_xor</function>
but adds the ability to set the initial value of the block counter to a non-zero value.
This permits direct access to any block without having to compute the previous ones.
</para>
<caution>
<para>
This encryption is unauthenticated, and does not prevent chosen-ciphertext attacks.
Make sure to combine the ciphertext with a Message Authentication Code,
for example with <function>sodium_crypto_aead_xchacha20poly1305_ietf_encrypt</function> function,
or <function>sodium_crypto_auth</function>.
</para>
</caution>
</refsect1>
<refsect1 role="parameters">
&reftitle.parameters;
<variablelist>
<varlistentry>
<term><parameter>message</parameter></term>
<listitem>
<para>
The message to encrypt.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>nonce</parameter></term>
<listitem>
<para>
24-byte nonce.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>counter</parameter></term>
<listitem>
<para>
The initial value of the block counter.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>key</parameter></term>
<listitem>
<para>
Key, possibly generated from <function>sodium_crypto_stream_xchacha20_keygen</function>.
</para>
</listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1 role="returnvalues">
&reftitle.returnvalues;
<para>
Encrypted message, &return.falseforfailure;.
</para>
</refsect1>
<refsect1 role="examples">
&reftitle.examples;
<example>
<title><function>sodium_crypto_stream_xchacha20_xor_ic</function> example</title>
<programlisting role="php">
<![CDATA[
<?php
$n2 = random_bytes(SODIUM_CRYPTO_STREAM_XCHACHA20_NONCEBYTES);
$left = str_repeat("\x01", 64);
$right = str_repeat("\xfe", 64);
// All at once:
$stream7_unified = sodium_crypto_stream_xchacha20_xor($left . $right, $n2, $key);
// Piecewise, with initial counter:
$stream7_left = sodium_crypto_stream_xchacha20_xor_ic($left, $n2, 0, $key);
$stream7_right = sodium_crypto_stream_xchacha20_xor_ic($right, $n2, 1, $key);
$stream7_concat = $stream7_left . $stream7_right;
var_dump(strlen($stream7_concat));
var_dump($stream7_unified === $stream7_concat);
?>
]]>
</programlisting>
&example.outputs.similar;
<screen>
<![CDATA[
int(128)
bool(true)
]]>
</screen>
</example>
</refsect1>
<refsect1 role="seealso">
&reftitle.seealso;
<para>
<simplelist>
<member><function>sodium_crypto_stream_xchacha20_xor</function></member>
</simplelist>
</para>
</refsect1>
</refentry>
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