# sodium_crypto_stream_xchacha20_xor_ic

(PHP 8 >= 8.2.0)

sodium_crypto_stream_xchacha20_xor_ic — Encrypts a message using a nonce and a secret key (no authentication)

### 说明

sodium_crypto_stream_xchacha20_xor_ic(
#[\SensitiveParameter] string `$message`,
string `$nonce`,
int `$counter`,
#[\SensitiveParameter] string `$key`
): string

The function is similar to sodium_crypto_stream_xchacha20_xor() 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.

警告

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 sodium_crypto_aead_xchacha20poly1305_ietf_encrypt() function, or sodium_crypto_auth().

### 参数

`message`

  The message to encrypt.

`nonce`

  24-byte nonce.

`counter`

  The initial value of the block counter.

`key`

  Key, possibly generated from sodium_crypto_stream_xchacha20_keygen().

### 返回值

Encrypted message, 或者在失败时返回 `false`.

### 示例

示例 #1 sodium_crypto_stream_xchacha20_xor_ic() example

`<?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);
?>`

以上示例的输出类似于：

    int(128)
    bool(true)

### 参见

- sodium_crypto_stream_xchacha20_xor() - Encrypts a message using a nonce and a secret key (no authentication)

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